May 27, 2010 ... This image from NASA's Airborne Visible/Infrared Imaging Spectrometer ... with unmatched spectral range, calibration accuracy and signal-to-noise ratio. ... The spectral image measurements are provided in orthorectified ...

There has been a strong, application driven development of Si-based cameras and spectrometers for imaging and spectral analysis of light in the visible and near infrared spectral range. This has resulted in very efficient devices, with high quantum efficiency, good signal to noise ratio and high resolution for this spectral region. Today, an increasing number of applications exists outside the spectral region covered by Si-based devices, e.g. within cleantech, medical or food imaging. We present a technology based on wavelength conversion which will extend the spectral coverage of state of the art visible or near infrared cameras and spectrometers to include other spectral regions of interest.

Results are reported for braod-band photometry of the BL Lac object AO 0235+164 carried out over the spectral range from 0.36 to 3.5 microns in December 1975 and in October and November 1976. It is found that the continuum of this object steepened at visible wavelengths between December 1975 and October 1976, but maintained a relatively constant slope in the near-IR despite a factor-of-ten decrease in flux from the maximum level. Visible-wavelength data are cited which appear to suggest that the steepening of the visible spectrum occurred in less than 300 days, while the near-IR level may have been nearly constant. It is shown that the observed change in the spectral shape of the visible-wavelength continuum cannot be explained in terms of a 'composite' model consisting of an unchanging galaxy and a varying nonthermal source with constant spectral index. Two other general classes of models are considered: intrinsic variability and extrinsic modulation.

Visual signalling can be affected by both the intensity and spectral distribution of environmental light. In shallow aquatic habitats, the spectral range available for visually mediated behaviour, such as foraging, can reach from ultraviolet (UV) to long wavelengths in the human visible range. However, the relative importance of different wavebands in foraging behaviour is generally unknown. Here, we test how the spectral composition of ambient light influences the behaviour of three-spined sticklebacks (Gasterosteus aculeatus) when foraging for live cladoceran Daphnia magna. Although paying particular attention to the UV waveband, we measured the foraging preferences of sticklebacks for prey presented under four different spectral conditions. These conditions selectively removed UV (UV-),...

We report the first realization, to the best of our knowledge, of a chirped multilayer dielectric mirror providing dispersion control over the spectral range of 300-900 nm and the first use of hafnium oxide in a chirped mirror. The technology opens the door to the reliable and reproducible generation of monocycle laser pulses in the blue-violet spectral range, will benefit the development of optical waveform and frequency-comb synthesizers over the ultraviolet-visible-near-infrared spectral range, and permits the development of ultrabroadband-chirped multilayers for high-power applications. PMID:17410276

We report on the fabrication and characterization of organic photodiodes deposited on ordinary newspaper sheets. Parylene acts as water and chemical barrier layer, an ORMOCER layer serves as an excellent smoothing and base layer for the diodes, which correspond to classical Tang-type bilayer cells. The photodiodes show excellent diode behaviour in current-voltage measurements of the devices under dark and illumination conditions. The spectral response covers the UV and visible spectral range.

In the present paper kinetics of emission spectra of the high voltage erosive water discharge at near ultraviolet and visible spectral ranges has been investigated. Obtained results show a similarity of physical properties of this discharge (and of corresponding plasmoids) to that of some other types of erosional discharges which also result in the formation of dust-gas fireballs.

Broad band UV-visible absorption spectroscopy is widely used to measure the concentration of radicals in reactive plasmas. We extended the applicability of this technique to the VUV (115 nm to 200 nm), the spectral range in which the electronic transitions from the ground state to the Rydbe...

Transmission spectra of wet human teeth and dentin slices, together with blood of different flow rates were investigated. The measurements carried out over a wide spectral range, from visible light down to terahertz radiation. The results make it possible to find the optimum light frequency for an all-optical determination of pulpal blood flow and, consequently, for clinically diagnosis of tooth vitality.

Experimental results of an investigation of aqueous ammonium oxalate solutions containing Cu(II) impurity by ultraviolet-visible spectroscopy are described and discussed from the standpoint of speciation of complexes. The results show that absorption of light by aqueous ammonium oxalate solutions containing Cu(II) impurity in the range -5 ultraviolet-visible spectral regions, and these changes may be expressed by full width at half maximum, molar extinction coefficient, peak wavelength and oscillator strength. The changes are caused by the coordination of C2O42- ligand with Cu(H2O)62+ aquocomplex, and are related with the impurity-solute concentration ratio ci/c. The coordination of C2O42- ligand with Cu(H2O)62+ aquocomplex in the range 0 ultraviolet spectral region but poor in the visible region.

Broadband focal plane array sensors, operating in the 0.25 to 2.5 ?m wavelength range, are an enabling technology for several imaging applications including atmospheric greenhouse gas monitoring. Currently, hyper-spectral imagers use separate image sensors for different spectral sub-bands, for example GaN for UV, Si for visible, and InGaAs for IR, thus requiring expensive component-level integration. Our approach is to manufacture a single image sensor with 0.25 to 2.5 ?m spectral range using GaAs substrates, which are commercially available in diameters as large as 6 inches. The key challenges, namely achieving high UV efficiency, low dark current, and high speed operation, are addressed separately in a lattice-matched GaAs UV-to-Visible photodiode and a lattice-mismatched InGaAs NIR-to-SWIR photodiode. The method for monolithically combining the two structures into a single UV-to-SWIR photodiode / photodiode array is also presented.

MicrOmega is an ultra miniaturized spectral microscope for in situ analysis of samples. It is composed of 2 microscopes; one with a spatial sampling less or equal to 4mm, working in 4 colors in the visible range: MicrOmega/VIS, and a NIR hyperspectral microscope working in the spectral range 0.9-4mm with a spatial sampling of 20mm per pixel: MicrOmega/IR (described in this paper). MicrOmega/IR illuminates and images samples a few mm in size and acquires the NIR spectrum of each resolved pixel in up to 320 contiguous spectral channels. The goal of this instrument is to analyze in situ the composition of collected samples at almost their grain size scale, in a non-destructive way. With the chosen spectral range and resolution, a wide variety of constituents can be identified: minerals, such ...

Results are assessed from a range of laboratories on spectral responsivity measurements in photodiodes. Data covariances demonstrated the necessity of more carefully analyzing the causes of discrepancies in measurements of photodiodes in the short-wavelength region and of introducing necessary changes in the measurement technique as well as in the organizational and procedural work in conducting the comparisons. It was found purposeful to expand the spectral range of the comparison, which encompasses not only the visible part of the spectrum but also the adjacent UV and near IR regions, which currently present great interest in radiometry.

UV-Vis- and infrared femtosecond spectroscopy makes it possible to reveal all different steps of photochemical reactions after the electronic excitation. The electronic relaxations are observed in the UV-Vis spectral range whereas the nuclear motions are monitored in the infrared spectral range. We used femtosecond time-resolved infrared spectroscopy to demonstrate the photoisomerization of the NO ligand photoinduced by a visible femtosecond pulse in a Na2[Fe(CN)5NO]·2H2O single crystal occurs in about 350 fs. The analysis of data makes it possible to unravel the mechanism leading to the photoisomerization of the NO ligand.

A well-adapted visible and infrared spectrograph has been developed for the SNAP (SuperNova/Acceleration Probe) experiment proposed for JDEM. The instrument should have a high sensitivity to see faint supernovae but also a good redshift determination better than 0.003(1+z) and a precise spectrophotometry (2%). An instrument based on an integral field method with the powerful concept of imager slicing has been designed. A large prototyping effort has been performed in France which validates the concept. In particular a demonstrator reproducing the full optical configuration has been built and tested to prove the optical performances both in the visible and in the near infrared range. This paper is the first of two papers. The present paper focus on the wavelength measurement while the second one will present the spectrophotometric performances. We adress here the spectral accuracy expected both in the visible and in the near infrared range in such configuration and we demonstrate, in particular, that the image...

Absorption spectroscopy and multi-angle scattering measurements in the visible spectral range are innovately used to analyze samples of extra virgin olive oils coming from selected areas of Tuscany, a famous Italian region for the production of extra virgin olive oil. The measured spectra are processed by means of the Principal Component Analysis method, so as to create a 3D map capable of clustering the Tuscan oils within the wider area of Italian extra virgin olive oils.

The Voyager IR investigation uses a Michelson interferometer with a 4.3-cm/sup -1/ spectral resolution in the 180--2500-cm/sup -1/ range and a single-channel radiometer for the visible and near-IR, 5000--30,000-cm/sup -1/. Both devices share a Cassegrain telescope with a 50-cm diam primary mirror and a 0.25 /sup 0/ field of view. Design, calibration, and performance are discussed along with a sample spectrum of Jupiter.

We review our work on the photo-induced insulator–metal transition in the strongly-correlated, spin-Peierls compound VO2. Our pump-probe experiments exploit the full spectral range of modern femtosecond science, combining time-resolved mid-IR and visible techniques with ultrafast soft x-ray absorption and hard x-ray diffraction. We also report on the switching behavior of VO2 nanoparticles embedded in Silica or in optical fibers, a new route to incorporate complex, photo-active materials into technologically viable environments.   

The luminescence of silver bromide crystals doped with praseodymium and erbium ions was investigated over the visible and near-infrared spectral regions. The emission, excitation, and absorption spectra, as well as kinetic parameters, were measured over a broad temperature range. The Judd-Ofelt analysis was used to calculate transition rates, branching ratios, and luminescence quantum efficiencies of rare-earth doped crystals. Good agreement between theoretical and experimental results was obtained. PMID:18264289

The Ocean Radiometer for Carbon Assessment (ORCA), currently being developed at Goddard, is a hyperspectral instrument with a spectral range extending from 350nm to 880nm in the UV and visible wavelength. Its radiometric measurement accuracy will depend, in part, on the extent to which it is insensitive to linearly polarized light. A wedge type depolarizer is used to reduce ORCA's polarization sensitivity over its entire spectral range. The choice for this approach is driven by the large spectral range and to a certain extent is also influenced by the currently orbiting SeaWifs instrument's use of a wedge depolarizer and its low polarization sensitivity. The wedge depolarizer's design, its modeled and measured depolarization characteristics are presented.

Spectral characteristics of ferri- and ferroderivatives of myoglobins have been studied in semiwater mammals. Extinction coefficients in the visible range of the spectrum have been determined for different derivatives of the studied heme proteins. It is established that variations in the maxima and minima of different absorption bands are inconsiderable. Close positions of isobestic points have been revealed for a system of oxyglobin and reduced myoglobin obtained from the muscles of the studied animals. Changes in spectral characteristics of methmyoglobins, induced by the effect of different pH, are identical, which evidences for similarity of the surroundings of active site of the studied heme proteins. PMID:1882458

We report on the fabrication and characterization of organic photodiodes deposited on ordinary newspaper sheets. Parylene acts as water and chemical barrier layer, an ORMOCER layer serves as an excellent smoothing and base layer for the diodes, which correspond to classical Tang-type bilayer cells. The photodiodes show excellent diode behaviour in current-voltage measurements of the devices under dark and illumination conditions. The spectral response covers the UV and visible spectral range. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

In supercontinuum generation, various propagation effects combine to produce a dramatic spectral broadening of intense ultrashort optical pulses. With a host of applications, supercontinuum sources are often required to possess a range of properties such as spectral coverage from the ultraviolet across the visible and into the infrared, shot-to-shot repeatability, high spectral energy density and an absence of complicated pulse splitting. Here we present an all-in-one solution, the first supercontinuum in a bulk homogeneous material extending from 450 nm into the mid-infrared. The spectrum spans 3.3 octaves and carries high spectral energy density (2 pJ nm(-1)-10 nJ nm(-1)), and the generation process has high shot-to-shot reproducibility and preserves the carrier-to-envelope phase. Our method, based on filamentation of femtosecond mid-infrared pulses in the anomalous dispersion regime, allows for compact new supercontinuum sources. PMID:22549836

Dwarf-planet (1) Ceres is one of the two targets, along with (4) Vesta, that will be studied by the NASA Dawn spacecraft via imaging, visible and near-infrared spectroscopy, and gamma-ray and neutron spectroscopy. While Ceres' visible and near-infrared disk-integrated spectra have been well characterized, little has been done about quantifying spectral variations over the surface. Any spectral variation would give us insights on the geographical variation of the composition and/or the surface age. The only work so far was that of Rivkin and Volquardsen ([2010], Icarus 206, 327) who reported rotationally-resolved spectroscopic (disk-integrated) observations in the 2.2-4.0mm range; their observations showed evidence for a relatively uniform surface. Here, we report disk-resolved observations...

A new semi-organic nonlinear optical material glycyl-l-alanine hydrochloride (GLAH) was grown successfully by slow evaporation solution growth method. The solubility of GLAH was estimated for a wide range of temperatures. Large size single crystal of size 15??9??6?mm3 was grown at room temperature. The grown crystal was subjected to single crystal X-ray diffraction study which confirms that the grown crystal is monoclinic in nature with the space group P21. The molecular weight of the title compound was estimated by mass spectrometry. Functional groups and the modes of vibrations were identified by FT-IR spectral analysis. The UV?visible spectral study reveals that the percentage of optical transmission of the sample is very high in the entire visible and UV regions. The second harmonic ...

The principal goal of the NASA Terrestrial Planet Finder (TPF) and ESA Darwin mission concepts is to directly detect and characterize extrasolar terrestrial (Earth-sized) planets. This first generation of instruments is expected to provide disk-averaged spectra with modest spectral resolution and signal-to-noise. Here we use a spatially and spectrally resolved model of the planet Mars to study the detectability of a planet's surface and atmospheric properties from disk-averaged spectra as a function of spectral resolution and wavelength range, for both the proposed visible coronograph (TPF-C) and mid-infrared interferometer (TPF-I/Darwin) architectures. At the core of our model is a spectrum-resolving (line-by-line) atmospheric/surface radiative transfer model which uses observational data as input to generate a database of spatially-resolved synthetic spectra for a range of illumination conditions (phase angles) and viewing geometries. Results presented here include disk averaged synthetic spectra, light-cur...

The mid-infrared spectral range (\\lambda ~ 2 \\mu m to 20 \\mu m) is known as the "molecular fingerprint" region as many molecules have their highly characteristic, fundamental ro-vibrational bands in this part of the electromagnetic spectrum. Broadband mid-infrared spectroscopy therefore constitutes a powerful and ubiquitous tool for optical analysis of chemical components that is used in biochemistry, astronomy, pharmaceutical monitoring and material science. Optical frequency combs, i.e. broad spectral bandwidth coherent light sources consisting of equally spaced sharp lines, have revolutionized optical frequency metrology one decade ago. They now demonstrate dramatically improved acquisition rates, resolution and sensitivity for molecular spectroscopy mostly in the visible and near-infrared ranges. Mid-infrared frequency combs have therefore become highly desirable and recent progress in generating such combs by nonlinear frequency conversion has opened access to this spectral region. Here we report on a pr...

TMC – Thermal Mapping Camera; HySI – Hyper Spectral Imager; LLRI – Lunar ... The PDS Imaging Node archives the Moon Mineralogy Mapper (M3) science ... electromagnetic radiation covering visible and near-infrared spectral regions.

OBJECTIVE: To distinguish components of vulnerable atherosclerotic plaque by imaging their energy response using spectral CT and comparing images with histology. METHODS: After spectroscopic calibration using phantoms of plaque surrogates, excised human carotid atherosclerotic plaques were imaged using MARS CT using a photon-processing detector with a silicon sensor layer and microfocus X-ray tube (50 kVp, 0.5 mA) at 38-?m voxel size. The plaques were imaged, sectioned and re-imaged using four threshold energies: 10, 16, 22 and 28 keV; then sequentially stained with modified Von Kossa, Perl's Prussian blue and Oil-Red O, and photographed. Relative Hounsfield units across the energies were entered into a linear algebraic material decomposition model to identify the unknown plaque components. RESULTS: Lipid, calcium, iron and water-like components of plaque have distinguishable energy responses to X-ray, visible on spectral CT images. CT images of the plaque surface correlated very well with histological photographs. Calcium deposits (>1,000 ?m) in plaque are larger than iron deposits (voxel using the energy range available. CONCLUSIONS: Spectral CT displays energy information in image form at high spatial resolution, enhancing the intrinsic contrast of lipid, calcium and iron within atheroma. KEY POINTS: • Spectral computed tomography offers new insights into tissue characterisation. • Components of vulnerable atherosclerotic plaque are spectrally distinct with intrinsic contrast. • Spectral CT of excised atherosclerotic plaques can display iron, calcium and lipid. • Calcium deposits are larger than iron deposits in atheroma. • Spectral CT may help in the non-invasive detection of vulnerable plaques. PMID:22760344

We present a method to obtain spectrally resolved images using upconversion. By this method an image is spectrally shifted from one spectral region to another wavelength. Since the process is spectrally sensitive it allows for a tailored spectral response. We believe this will allow standard silicon based cameras designed for visible/near infrared radiation to be used for spectral images in the mid infrared. This can lead to much lower costs for such imaging devices, and a better performance.

Disability glare, affecting e.g. road safety at night, may result either from intraocular light scattering or from external conditions such as fog. Measurements were made of light scattering in fog and compared with intraocular straylight data for normal eyes and eyes with simulated cataract. All measurements were made with a direct compensation flicker method. To estimate light scattering levels in fog, straylight measurements were carried in a fog chamber for different densities of fog. Density was characterized by the meteorological term visibility V and ranged from 7 to 25. Test distance for measurements in the fog was constant at 5 m. Cataract eye conditions were simulated by placing a light scattering polymer dispersed liquid crystal (PDLC) filter with scatterers of submicron size in front of the normal eye. All measurements were made using each of three broad-band color stimuli - red, green and blue (produced either with LEDs or a color CRT monitor). Differences were found in both the level and the spectral characteristics of scattering under the different conditions. The measured values of the straylight parameter, s, in artificial fog showed no noticeable spectral dependence at any visibility range. Increasing the visibility range caused an exponential decrease in the straylight. Intraocular straylight measured with the clear eye showed an increase at the red and blue ends of the spectrum as compared to the green. Straylight measured using PDLC plates with different transparency levels showed a spectral dependence which decreased with wavelength. The scattering introduced by the PDLC plate therefore failed to give a valid simulation of cataract and fog conditions for polychromatic stimuli, due to its erroneous spectral dependence. PMID:19422568

Signal estimates are crucial to the design of time-resolved pyrometry measurements. These estimates affect fundamental design decisions, including the optical relay (fiber versus open beam), spectral range (visible or infrared), and amplification needs (possibly at the expense of time resolution). The pyrosim program makes such estimates, allowing the collected power, photon flux, and measured signal to be determined in a broad range of pyrometry measurements. Geometrical collection limits can be applied; sample emissivity, transfer efficiency, and detector sensitivity may also be specified, either as constants or functions of wavelength.

We investigate the optical properties of mono- and double-layer asymmetric fishnet metamaterials with orientated elliptical holes, which exhibit exotic spectral and polarization rotating characteristics in the visible spectral range. Our results show that nontrivial orientations of the holes with respect to the reciprocal lattice vectors of the periodic lattice in both systems produce strong polarization rotation as well as additional enhanced optical transmission peaks. Analysis of the electromagnetic field distribution shows the unusual effect is produced by the spinning localized surface plasmon resonances due to the asymmetric geometry. High sensitivity of the hybridized mode on the dielectric spacing, the aspect ratio of the holes and the embedding media in double-layer structure is also observed. The dependence of spectral and polarization response on the orientation of the holes and the embedding media is useful for design of chiral metamaterials at optical frequencies and tailoring the polarization behavior of the metallic nano-structures. PMID:22565701

Saturn's main rings exhibit variations in both their opacity and spectral properties on a broad range of spatial scales, and the correlations between these parameters can provide insights into the processes that shape the composition and dynamics of the rings. The Visual and Infrared Mapping Spectrometer (VIMS) instrument onboard the Cassini Spacecraft has obtained spectra of the rings between 0.35 and 5.2 microns with sufficient spatial resolution to discern variations on scales below 200 km. These relatively high-resolution spectral data reveal that both the depths of the near-infrared water-ice absorption bands and the visible spectral slopes are often correlated with structural parameters such as the rings' optical depth. Using a simplified model for the ring-particles' regolith properties, we have begun to disentangle the trends due to changes in the gross composition of the ring particles from those that may be due to shifts in the texture of the ring particles' regolith. Consistent with previous studie...

Objective The study was conducted to observe the spectral reflectance curves, and evaluate the color coordinates (CIELAB) of VM7 dentin ceramics (VITA, Germany) across the whole 3D-MASTER shade system. Methods Three disc samples, 13mm in diameter and 1.4mm in thickness, were produced for each shade by firing following the manufacturers instructions. Each fired disc was ground to a thickness of 1.0mm and both faces were polished. Spectral reflectance data in the visible spectrum under the standard illuminant D65 were collected at 1nm intervals by using a computer-controlled spectrophotometer. Color coordinates, L*, a*, b*, C*, h, in the three-dimensional CIELAB color space were obtained. Results (1) Spectral reflectance in the short-wavelength range systematically decreased with increasing ...

The present study explored the use of narrow-band indices formulated in the visible spectral region at leaf and canopy levels to estimate carotenoid content. The research area was a pine forest affected by decline processes. Spectral reflectance and pigment content including chlorophylls a and b (Ca+b), carotenoid (Cx+c) and xanthophyll cycle pigments (VAZ) were measured in needles for two consecutive years. The study was conducted using radiative transfer modeling methods and high-resolution airborne imagery acquired at 10nm FWHM bandwidth. Airborne data consisted of high spatial resolution imagery acquired with a narrow-band multispectral camera on board an unmanned aerial vehicle (UAV). The imagery had 50cm resolution and six spectral bands in the 500-800nm range, enabling the identific...

Abstract- The 0.35-2.5 mm reflectance spectra of iron meteorite powders and slabs have been studied as a function of composition, surface texture (for slabs), grain size (for powders), and viewing geometry (for powders). Powder spectra are invariably red-sloped over this wavelength interval and have a narrow range of visible albedos (approximately 10-15% at 0.56 mm). Metal (Fe:Ni) compositional variations have no systematic effect on the powder spectra, increasing grain size results in more red-sloped spectra, and changes in viewing geometry have variable effects on overall reflectance and spectral slope. Roughened metal slab spectra have a wider, and higher, range of visible albedos than powders (22-74% at 0.56 mm), and are also red-sloped. Smoother slabs exhibit greater differences from ...

A space-adapted visible and infrared spectrograph has been developed for the SNAP (SuperNova/Acceleration Probe) experiment proposed for JDEM. The instrument should have a high sensitivity to see faint supernovae, but also a good redshift determination better than 0.003(1+z), and a precise spectrophotometry (2%). An instrument based on an integral-field method with the powerful concept of imager slicing has been designed. A large prototyping effort has been performed in France that validates the concept. In particular, a demonstrator reproducing the full optical configuration has been built and tested to prove the optical performance both in the visible and in the near-infrared range. This article, the first of two, focuses on wavelength measurement, while the second article will report on spectrophotometric performance. We address here the spectral accuracy expected both in the visible and in the near-infrared range in such a configuration, and we demonstrate, in particular, that the image slicer enhances the instrumental performances in the spectral measurement precision by removing the slit effect. This work is supported in France by CNRS/INSU/IN2P3 and by the French space agency (CNES), and in the US by the University of California.

A photoacoustic spectrometer for the measurement of aerosol absorption spectra, based on the excitation of a pulsed nanosecond optical parametrical oscillator (OPO), will be introduced. This spectrometer is working at ambient pressure and can be used to detect and characterize different classes of aerosols. The spectrometer features a spectral range of 410 to 2500 nm and a sensitivity of 2.5 × 10(-7) m(-1) at 550 nm. A full characterization of the system in the visible spectral range is demonstrated, and the potential of the system for near IR measurement is discussed. In the example of different kinds of soot particles, the performance of the spectrometer was assessed. As we demonstrate, it is possible to determine a specific optical absorption per particle by a combination of the new spectrometer with an aerosol particle counter. PMID:23035870

A system for measuring radiation in the laboratory or at a site to aid in determining whether to erect a solar energy installation at that site includes a positioner and a sensor. The sensor, which is mounted on the positioner, includes a rotating semispherical chopper and an integrating sphere for collecting radiation in three modes. A broad-band detector measures the irradiance from the integrating sphere to monitor for anomalies. A pair of monochromators simultaneously measure, one in the visible range and the other in the infrared range, the spectral irradiance from the integrating sphere. Processing electronics process the measured spectral irradiance from the monochromators and generate data signals for providing an absolute irradiance spectrum at the plane of the entrance aperture. The absolute irradiance spectrum is inputted to an X-Y plotter and a magnetic disc and tape. The system further includes internal reference sources providing continuous wavelength and irradiance calibration.

Special glass with reflective coatings has found wide applications in architecture. Thin coatings deposited on glass panes modulate the glass optical properties. Some of the coatings operate as a mirror for long-wave infrared radiation of building interiors. The thin films have high transmittance in visible range and very high reflectance in long-wave infrared range. These coatings limit absorption of infrared radiation in the glass. They have low emissivity. It means radiation heat losses of the coated glazing are reduced. The design of coatings for window glazing applications should be based on the study of optical spectral properties of glass and thin film materials. Optical properties of thin films are determined by spectral characteristics as reflectance, transmittance and absorptance...

The transient absorption induced by picosecond pulse radiolysis in the windows of a fused silica optical cell is investigated with pump probe techniques in the UV and the visible range. After excitation with an electron pulse of 7 MeV and an effective duration of around 10 ps the absorbance changes during relaxation are recorded up to nanoseconds with a supercontinuum and a single wavelength probe at 263 nm. The complex spectral signatures and kinetics of the empty cell are set into relation with the transient absorption of water radiolysis. Special care is taken to assure equal irradiation conditions for the comparative measurements over the large spectral range. The results reveal clearly that the transient absorption induced in the fused silica cell is not negligible. The transient signals due to the cell should be considered in picosecond pulse radiolysis of solutions in order to avoid important errors on the time dependent yield of transient species, particularly of those absorbing in the UV.

The effect of lateral intraband photoconductivity in undoped InAs/GaAs heterostructures with quantum dots (QDs) has been studied, with QD levels populated with carriers by means of interband optical excitation of varied power at different wavelengths. In the absence of interband illumination, no photoconductivity is observed in the mid-IR spectral range. At the same time, additional exposure of the structures to visible or near-IR light gives rise to a strong photoconductivity signal in the mid-IR spectral range (3?5 ?m), associated with intraband transitions in QDs. The signal is observed up to a temperature of ?200 K. Use of interband optical pumping makes the intraband photoconductivity signal stronger, compared with similar structures in which doping serves to populate QD levels.

This paper points out fields for a useful application of IR-photography and thermography in brown coal surface mining. Measurements are conducted within the range of 0.7 to 1.3MUm wave length for IR-photography and 2.0 to 5.5 MUm as well as 8.0 to 14.0 MUm wave length for thermographic measurements. Spectral or integral reflection and emission measurements are possible. Combined interpretation of measurements within the visible spectral range and selected IR spectra is recommended. Infrared and thermographic methods were successfully employed in localizing water bearing strata in overburden slopes, mapping of wet fields in mine sections and working levels, determining disturbances in overburden and coal strata, differentiating coal and overburden strata as well as nonhomogeneity in spoil banks and locating underground voids and abandoned roadways in the overburden. (4 refs.) (In German)

We present a novel microspectrometer-on-chip for the visible spectral region, consisting of a tunable MEMS Fabry-Perot interferometer (FPI) monolithically integrated on a PIN photodiode using IC compatible microfabrication techniques. MEMS FPI is an electrostatically (AC voltage) actuated structure consisting of two parallel atomic layer deposited Bragg mirror stacks of Al2O3/TiO2 with imbedded circular aluminum electrodes on top and the bottom for capacitive tuning capability for the wavelength range of 420-550nm. The fabrication process flow for the successful completion of the device is presented. The spectral response of the device ranges from 0.1A/W at l=420nm to 0.2A/W at l=550nm, with transmission peak width of 8nm at 540nm. These results indicate photodiode performance that matches...

Lanthanide-doped upconverting nanoparticles (UCNPs) have recently attracted enormous attention in the field of biological imaging owing to their unique optical properties (near-infrared excitation followed by photoluminescence in the visible spectral range). For biological applications, it is critical to understand the interaction between these nanoparticles and biological systems at the cellular level. In this paper, using epi-fluorescence microscopy with 980-nm excitation, a full intracellular pathway composed of endocytosis, active transport, and exocytosis was clearly visualized for PEG-phospholipid-coated UCNPs in single HeLa cells, which was experimentally feasible mostly thanks to the excellent photostability and low cytotoxicity thereof. Each step in the pathway was characterized a...

We have begun to create a comprehensive set of thermal infrared (TIR, approx. 1650-200/cm, approx. 6-50 microns) spectra of palagonitic and hydrothermally altered soils that exhibit a range of mineralogical and chemical compositions for use in analyzing MGS TES data. Palagonite, a phyllosilicate-poor hydrolytically altered tephra, has been suggested as a possible component of the martian soil/dust based on visible and near infrared (VNIR) spectral similarities with martian dusty regions. The chemistry and crystallinity of altered tephras are highly variable depending on the parent material and local environmental conditions, and are important indicators of alteration processes.

This work will report on the first work on the characterization of a back-thinned Vanilla-a 512×512 (25 ?m squared) active pixel sensor (APS). Characterization of the detectors was carried out through the analysis of photon transfer curves to yield a measurement of full well capacity, noise levels, gain constants and linearity. Spectral characterization of the sensors was also performed in the visible and UV regions. A full comparison against non-back-thinned front illuminated Vanilla sensors is included. Such measurements suggest that the Vanilla APS will be suitable for a wide range of applications, including particle physics and biomedical imaging.

A bulk heterojunction of porous silicon and eumelanin, where the columnar pores of porous silicon are filled with eumelanin, is proposed as a new organic-inorganic hybrid material for photovoltaic applications. The addition of eumelanin, whose absorption in the near infrared region is significantly higher than porous silicon, should greatly enhance the light absorption capabilities of the empty porous silicon matrix, which are very low in the low energy side of the visible spectral range (from about 600?nm downwards). The experimental results show that indeed the photocarrier collection efficiency at longer wavelengths in eumelanin-impregnated samples is clearly higher with respect to empty porous silicon matrices. PMID:21858346

This invention aims to provide a photoelectric conversion element which is cheap and easy to prepare a large surface, with flexibility and high conversion efficiency, and is in good balance with the spectral distribution of solar and room lights. For this purpose, when an organic semiconductor which can form a photocarrier in the visible light range is used alone or jointly with a binder, triphenylamine compound e.g., triphenylamine, diphenyl(trimethylphenyl)amine greatly increase the photo-current thus enhancing the photoelectric conversion efficiency. The front electrode layer is made of Al, lead, zinc, platinum and tin oxide. The substrate is glass or transparent plastic film. 1 fig.

A new type of pulse high voltage electric discharge through a thin conducting layer on the surface of glass plate has been investigated. The afterglow plasma of this discharge forms quasi-spherical object with a lifetime about 0.2-0.3 s. Electric properties of the objects were studied by electric probe method. Measurements of plasma radiation spectra kinetics at visible and near ultraviolet spectral ranges have been carried out. Comparative analysis of the physical properties of the plasmoids appearing in this discharges and of ones generated via thin metal wires burning is given. Possible mechanism of the plasma metastability are discussed.

We studied the transmittance and reflectance of the low-dimensional Mott-Hubbard insulator TiOCl in the infrared and visible frequency range as a function of pressure. The strong suppression of the transmittance and the abrupt increase of the near-infrared reflectance above 12 GPa suggest a pressure-induced insulator-to-metal transition. The pressure-dependent frequency shifts of the orbital excitations, as well as the pressure dependences of the charge gap and the spectral weight of the optical conductivity above the phase transition are presented.

The nature of solute-solvent interactions in ternary solutions of rifampicin-water-ethanol was investigated by means of electronic absorption spectra recorded in visible and in ultraviolet range respectively. Measurements upon the frequency in the absorption band maxima were carried out, the mathematical interpretation of the solvent spectral shifts, on the basis of Bakhshiev's theory, leading to the emphasizing of orientation and dynamic forces. Molecular orbital modeling applied by means of specialized soft, resulted in the computational approach of rifampicin dipole moment and intramolecular hydrogen bond lengths, evidencing also four metastable conformers.

Magneto-optical properties of a ferromagnetic semiconductor (Zn,Cr)Te were investigated through magnetic circular dichroism (MCD) measurements in the visible spectral range. (Zn,Cr)Te films without and with an additional nitrogen (N) doping as an acceptor exhibited different MCD spectra around the {gamma} point; a broad MCD band extending over a few hundred meV was observed in the undoped (Zn,Cr)Te while a relatively sharp peak appeared in the heavily N-doped (Zn,Cr)Te. The different MCD spectra are considered to be correlated with the change in the Cr valence state due the acceptor doping. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Raman cross-sections of explosives in solution and in the solid state have been measured using visible and near-infrared excitation via secondary calibration. These measurements are valuable for both fundamental scientific purposes and applications in the standoff detection of explosives. The explosive compounds RDX, HMX, TNT, 2,4-DNT, 2,6-DNT, and ammonium nitrate were measured using discrete excitation wavelengths ranging from 532 nm to 785 nm. A comparison of the spectral features and cross-sections between the solid state and solution was performed. Comparison is also made to cross-sections measured with deep ultraviolet excitation. PMID:22732533

By applying ellipsometry and extending the measurements from visible to mid infrared spectral range we examined the complex dielectric function of thin layers grown into silicon. The layers were synthesized by high-temperature (1050^oC) annealing in oxidizing ambient of plasma immersion N^+ ion implanted Si substrates. Si?N, Si?N?O and Si?Si chemical bonds in the silicon oxide network were identified and confirmed by X-ray photoelectron spectroscopy (XPS). Depending on N^+ fluence (10^1^6-10^1^8N^+/cm^2) and annealing duration (10 and 20min) the grown layers were identified either as silicon oxynitride with considerably low N content or silicon dioxide enriched with nitrogen.

Scanning and transmission electron microscopy reveal that SiOx/Si layers can roll-up into microtubes and radial superlattices on a Si substrate. These hybrid objects are thermally stable up to 850 C and emit light in the visible spectral range at room temperature. For tubes disengaged from the substrate surface, optically resonant emission with mode spacings inversely proportional to the tube diameter are observed and agree excellently with those obtained from Finite-Different-Time-Domain simulations. The resonant modes we record are strictly polarized along the tube axis.

We demonstrate a simple method for infrared few optical-cycle pulse generation, which is based on collinear visible-to-infrared frequency conversion and involves difference-frequency generation and subsequent two-step optical parametric amplification. The numerical simulations and experiments using BBO crystals show an efficient frequency down conversion of visible ˜20 fs pulses from a commercial blue-pumped noncollinear optical parametric amplifier yielding 1.2-2.4 ?m tunable sub-100 ?J pulses with duration of 3 to 5 optical-cycles. The proposed method could be readily extended to generate few optical-cycle pulses in the mid-infrared spectral range (up to 5.5 ?m) using, e.g., LiIO3 and LiNbO3 crystals, as demonstrated by the numerical simulations. In these crystals, even shorter, two-optical-cycle mid-infrared pulses could be obtained at particular wavelengths where group velocity matching between the signal and idler waves is achieved.

Silica glasses doped with LaF3 nanocrystals were prepared by HF-catalyzed sol-gel method. HF was used both as fluorine source and as catalyst of the sol-gel reaction, making it possible to shorten the processing time with reducing the concentration of SiOH groups to ~10^1^8cm^-^3. The resultant glasses are transparent at visible spectral range, and the optical loss at the ultraviolet absorption edge is dominated by the Rayleigh scattering from LaF3 crystallites. The size of LaF3 crystallites increases with an increase in the sintering temperature and time, and is smaller than ~40nm in samples showing good visible transparency. Green upconversion photoluminescence is observed in an Er^3^+-doped sample under excitation at 980nm.

Area array sensors operating in the visible portion of the spectrum can provide imagery suitable for real time and near real time tactical reconnaissance applications. Recent CCD sensor developments, image compression developments and developments in imaging system hardware are enabling greater volumes of imagery to be collected, stored, processed and transmitted to support tactical applications. Area array CCDs with 6000 X 6000 pixels or larger can provide synoptic coverage with good resolution. ITO clock electrode architectures enable extended spectral range and higher responsivity while real time compression permits data transfer of image files in near real time. Flight testing of evolving hardware systems is under way to demonstrate overall system capabilities. The Tier II+ visible EO camera is an example of evolving capability.

The new synchrotron-radiation circular-dichroism (SRCD) endstation on the UV-visible synchrotron beamline DISCO has been commissioned at the SOLEIL synchrotron. The design has been focused on preservation of a high degree of linear polarization at high flux and moderate resolving power covering the vacuum ultraviolet to visible spectral range (125-600-nm). The beam dimensions have been set to 4-mm 4-mm at 1-nm bandwidth for lower sample degradation. The nitrogen-purged sample chamber fits three types of sample holders accommodating conventional round cell mounting, automated rotation of the samples, as well as a microfluidic set-up. Automated temperature-controlled data collection on microvolumes is now available to the biology and chemistry communities. Macromolecules including membrane p...

Acousto-optic tunable-filter (AOTF) technology has been used in the design of a no-moving parts, compact, lightweight, field portable, automated, adaptive spectral imaging system when combined with a high sensitivity imaging detector array. Such a system could detect spectral signatures of targets and/or background, which contain polarization information and can be digitally processed by a variety of algorithms. At the Army Research Laboratory, we have developed and used a number of AOTF imaging systems and are also carrying out the development of such imagers at longer wavelengths. We have carried out hyperspectral and multispectral imaging using AOTF systems covering the spectral range from the visible to mid-IR. One of the imager uses a two-cascaded collinear-architecture AOTF cell in the visible-to-near-IR range with a digital Si charge-coupled device camera as the detector. The images obtained with this system showed no color blurring or image shift due to the angular deviation of different colors as a result of diffraction, and the digital images are stored and processed with great ease. The spatial resolution of the filter was evaluated by means of the lines of a target chart. We have also obtained and processed images from another noncollinear visible-to-near-IR AOTF imager with a digital camera, and used hyperspectral image processing software to enhance object recognition in cluttered background. We are presently working on a mid-IR AOTF imaging system that uses a high- performance InSb focal plane array and image acquisition and processing software. We describe our hyperspectral imaging program and present results from our imaging experiments.

High resolution spectroscopy experiments with visible adaptive optics (AO) telescopes at Starfire Optical Range and Mt. Wilson have demonstrated that spectral resolution can be routinely improved by a factor of - 10 over the seeing-limited case with no extra light losses at visible wavelengths. With large CCDs now available, a very wide wavelength range can be covered in a single exposure. In the near future, most large ground-based telescopes will be equipped with powerful A0 systems. Most of these systems are aimed primarily at diffraction-limited operation in the near IR. An exciting new opportunity will thus open up for high resolution IR spectroscopy. Immersion echelle gratings with much coarser grooves being developed by us at LLNL will play a critical role in achieving high spectral resolution with a compact and low cost IR cryogenically cooled spectrograph and simultaneous large wavelength coverage on relatively small IR detectors. We have constructed a new A0 optimized spectrograph at Steward Observatory to provide R = 200,000 in the optical, which is being commissioned at the Starfire Optical Range 3.5m telescope. We have completed the optical design of the LLNL IR Immersion Spectrograph (LISPEC) to take advantage of improved silicon etching technology. Key words: adaptive optics, spectroscopy, high resolution, immersion gratings

Calibrated values of incident spectral irradiance are reported from the Healy Oden Transarctic Experiment during August and September 2005. Spectra were obtained for a wide range of solar zenith angles, cloud conditions, and surface types to provide basic data for regional shortwave radiative energy balance calculations as well as climate model parameterization and validation. Supervised principal component analysis on the spectral continuum showed that three principal components explain over 99% of the variance resulting from darkening across the solar spectrum with increasing cloud cover by volume scattering, from stronger attenuation in the solar infrared relative to visible wavelengths by H2O, and from Rayleigh scattering. Comparison of the observations with the atmospheric radiation model SBDART showed that good agreement was obtained varying only the cloud optical depth. Applying the model, we showed how the surface albedo affects incident spectral irradiance under clear as well as cloudy skies, and we obtained a quantitative estimate of the visual effects of ``water sky'' and ``ice blink.'' We also determined the spectral albedo of the atmosphere for a dense arctic stratus cloud deck decoupled from the influence of the underlying surface. Incident spectral irradiances were integrated numerically and compared with calibrated pyranometer observations. Agreement was within 5% for cases where the cloud transparency and incident irradiance did not fluctuate strongly over the 10-min pyranometer recording intervals. A new set of values for total albedo for clear versus cloudy conditions at high and low Sun angles is presented for six prominent arctic surface types.

We numerically study the artificial spectral-filtering effect in dissipative soliton fiber lasers without intracavity spectral filters. It is found that in dissipative soliton lasers with real saturable absorbers (SAs), the dynamic spectral filtering of the real SAs serves as an artificial spectral filter and contributes to the pulse shaping. While in the dissipative soliton lasers with artificial SAs, such as nonlinear polarization rotation, the spectral filtering introduced by the intracavity polarization-dependent components acts as an artificial spectral filter and shapes the pulses to obtain mode-locking. An investigation of the artificial spectral-filtering effect reveals the operating mechanisms of the dissipative soliton fiber lasers without visible bandpass filters.

A large variety of angularly selective fenestration systems have been developed in the past two decades and show great potential in improving visual comfort while reducing energy consumption, especially when combined with spectrally selective properties. Such systems include light-redirecting glazing, shading, film coatings, reflectors and others. To assess the potential of these systems accurately and reliably, one needs to be able to predict in detail how they modify the energy, direction and spectral make-up of solar radiation. For this assessment, spectral (wavelength-dependent) Bidirectional Transmission or Reflection Distribution Functions are used, usually referred to as BTDFs or BRDFs, or more generally BSDFs for Scattering Functions. To enable a faster, cheaper, and continuous investigation of these properties over most of the solar spectrum (400-1700 nm), an innovative goniospectrometric instrument has been created, relying on digital imaging, on light collection by an ellipsoidal half-transparent mirror, and on a filtering method in the visible range to generate spectral radiometric BSDFs. This so-called Heliodome instrument is described in this paper. It enables the performance of new fenestration technologies to be assessed in terms of lighting and solar gains management potential. The rotating table also serves as a heliodon, an architectural design tool for visualizing sunlight distribution inside a scale model and performing analyses on appropriate sun control strategies. The Heliodome's major innovations compared to other devices are to enable an analysis of both the visible and the near-infrared portions of the solar spectrum, to provide spectral as well as photometric light distribution data, and to ensure a continuous investigation of the transmitted or reflected light in a time-efficient way. (author)

The data analysis program, SPECTRUM, is used for fusion, visualization, and classification of multi-spectral imagery. The raw data used in this study is Landsat Thematic Mapper (TM) 7-channel imagery, with 8 bits of dynamic range per channel. To facilitate data transmission and storage, a compression algorithm is proposed based on spatial wavelet transform coding and KLT decomposition of interchannel spectral vectors, followed by adaptive optimal multiband scalar quantization. The performance of SPECTRUM clustering and visualization is evaluated on compressed multispectral data. 8-bit visualizations of 56-bit data show little visible distortion at 50:1 compression and graceful degradation at higher compression ratios. Two TM images were processed in this experiment: a 1024 x 1024-pixel scene of the region surrounding the Chernobyl power plant, taken a few months before the reactor malfunction, and a 2048 x 2048 image of Moscow and surrounding countryside.

Optical anisotropy of synthetic opals has been investigated by measuring the spectral dependence of polarized transmitted light at normal and oblique light incidence at various sample azimuth orientations. The optical anisotropy of thin films and bulk samples has been measured by the polarization modulation technique in the visible spectral range. The observed optical anisotropy of synthetic opals was caused by several contributions. (i) Internal strain induced during the growth process. The optical anisotropy axes along [1 1 0] and [1¯12] directions in opal lattice of fcc symmetry were indicated in the (1 1 1) plane for both thin films and bulk samples of synthetic opal. (ii) Particular features of Brillouin zone manifesting themselves as the 3rd and 6th order rotation axes in the azimuth-resolved dependence of anisotropy parameters in the (1 1 1) plane. (iii) Oblique light incidence leading to the anisotropy with respect to the incidence plane.

We report on the generation of third-order (TH) and high-order harmonics (HH) directly inside a self-guided femtosecond filament in air. By terminating the filament with a steep density gradient behind a pinhole placed at different distances from the geometric focus, the evolution of the generated radiation is tracked along the nonlinear interaction zone. Spectra are recorded in the visible (VIS), ultraviolet (UV) and extreme ultraviolet (XUV) spectral range under identical conditions. The VIS and UV spectral bandwidth undergoes significant broadening. The input pulse parameters are varied systematically to optimize the TH bandwidth. Recorded spectra show Fourier-limits below 5?fs pulse duration centered at 264?nm wavelength. We observe conversion to HH up to the 25th order and use the HH ...

Mass spectrometry imaging by Fourier transform ion cyclotron resonance (FT-ICR) yields hundreds of unique peaks, many of which cannot be resolved by lower performance mass spectrometers. The high mass accuracy and high mass resolving power allow confident identification of small molecules and lipids directly from biological tissue sections. Here, calibration strategies for FT-ICR MS imaging were investigated. Sub-parts-per-million mass accuracy is demonstrated over an entire tissue section. Ion abundance fluctuations are corrected by addition of total and relative ion abundances for a root-mean-square error of 0.158 ppm on 16,764 peaks. A new approach for visualization of FT-ICR MS imaging data at high resolution is presented. The "Mosaic Datacube" provides a flexible means to visualize the entire mass range at a mass spectral bin width of 0.001 Da. The high resolution Mosaic Datacube resolves spectral features not visible at lower bin widths, while retaining the high mass accuracy from the calibration methods discussed.

Imaging spectrometers or {open_quotes}Hyperspectral Sensors{close_quotes} simultaneously collect spectral data as both images and as individual spectra. A broad range of techniques have been examined, refined, and put into operational practice for analysis of geologic problems. This paper describes a successful geologic case history using an end-to-end approach on Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data, including data calibration to reflectance, use of a linear transformation to minimize noise and determine data dimensionality, location of the most spectrally pure pixels, extraction of end member spectra, and spatial mapping of specific end members. Several supporting case studies using AVIRIS data of near-shore marine environments demonstrate the viability of these methods for studying the coastal zone. The methods described provide a starting point for image segmentation, material identification, and mapping of marine processes in the near-shore environment.

A self-amplified spontaneously emitting (SASE) free-electron laser (FEL) for the visible-to-ultraviolet spectral range is under construction at the Advanced Photon Source at Argonne National Laboratory. The amplifier part of the FEL consists of twelve identical 2.7-m-long sections. Each section includes a 2.4-m-long, 33-mm-period hybrid undulator, a quadrupole lens, and a set of electron beam and radiation diagnostics equipment. The undulators will operate at a fixed magnetic gap (approx. 9.3 mm) with K=3.1. The electron beam position will be monitored using capacitive beam position monitors, YAG scintillators with imaging optics, and secondary emission detectors. The spatial distribution of the photon beam will be monitored by position sensitive detectors equipped with narrow-band filters. A high-resolution spectrograph will be used to observe the spectral distribution of the FEL radiation.

Revealing the nature of charge excitations in strongly correlated electron systems is crucial to understanding their exotic properties. Here we use broadband ultrafast pump-probe spectroscopy in the visible range to study low-energy transitions across the Mott-Hubbard gap in the orbitally ordered insulator YVO3. Separating thermal and nonthermal contributions to the optical transients, we show that the total spectral weight of the two lowest peaks is conserved, demonstrating that both excitations correspond to the same multiplet. The pump-induced transfer of spectral weight between the two peaks reveals that the low-energy one is a Hubbard exciton, i.e., a resonance or a nearly bound state between a doublon and a holon. Finally, we speculate that the pump-driven spin disorder can be used to quantify the kinetic energy gain of the excitons in a ferromagnetic environment.

A dedicated mission to investigate exoplanetary atmospheres represents a major milestone in our quest to understand our place in the universe by placing our Solar System in context and by addressing the suitability of planets for the presence of life. EChO -the Exoplanet Characterisation Observatory- is a mission concept specifically geared for this purpose. EChO will provide simultaneous, multi-wavelength spectroscopic observations on a stable platform that will allow very long exposures. EChO will build on observations by Hubble, Spitzer and groundbased telescopes, which discovered the first molecules and atoms in exoplanetary atmospheres. EChO will simultaneously observe a broad enough spectral region -from the visible to the mid-IR- to constrain from one single spectrum the temperature structure of the atmosphere and the abundances of the major molecular species. The spectral range and resolution are tailored to separate bands belonging to up to 30 molecules to retrieve the composition and temperature str...

Optical properties of the biopolymers chitin and chitosan have been considered for wavelengths between 250 and 750nm. First, by inverting published refractive index data for composite chitosan-chitin samples of two independent sources, we have been able to obtain the spectral dependence of both the chitosan and chitin refractive indices. Then light reflection and transmission measurements were carried out for samples obtained from fresh shrimp shells. From these spectrophotometric measurements the chitin refractive index and its extinction coefficient have been obtained for the mentioned spectral range. Absorption of light by chitin is negligible for visible wavelengths. Chitin extinction coefficient displays absorption bands in the near ultraviolet, and it is attributed to the proteinaceo...

Abstract Silicon nanowires (SiNWs) arrays prepared by silver-assisted chemical etching show ultra-low reflectance over the wide spectral bandwidth from 300 to 1000 nm. In this work, SiNWs arrays were prepared by using solar-grade multi-crystalline (mc-Si-pn) and single crystalline (sc-Si-pn) silicon(100) wafers. Reflectance is significantly decreased over the visible-light spectral range with increase in the length of nanowires by almost 5 and 3 times for multi-crystalline and single crystalline Si samples, respectively. However it is noted that there is no further reduction in the reflectance when the length of nanowires is beyond 400 nm for mc-Si-pn and 300 nm for sc-Si-pn samples. Also, the reflectance data and scanning electron microscope (SEM) images indicate that the density of nanow...

A wide-band spectral diagnostic system based on dispersion property of the Zinc Selenide prism, a crystalline material highly dispersive in the near-to-far infrared spectral range, has been studied and developed for the laser wakefield acceleration experiment at LOA for the measurement of few femto-seconds long electron beam. The extensive PIC simulation studies of the colliding-beam LWFA have shown very short electron beam duration of less than 10 femtoseconds. The prism spectrometer diagnostic with highly sensitive Mercury Cadmium Telluride infrared detector and the diffraction-grating spectrometer with a high-resolution imaging visible camera together have the spectral range coverage and resolution capable of detecting ultra-short Coherent Transition Radiation (CTR) generated by interaction of bunch charges with a 100 microns thickness aluminum foil. The beam profile of asymmetric shape then could be extracted from the CTR spectrum by inverse Fourier transformation with Kramers-Kronig relation. The diagnostic system has been tested and calibrated for characterization of blackbody source spectrum and spectral responsivity. The measurement of electron beam duration of few femtoseconds has yet been convincingly shown with high resolution, and the measurements of this kind have important implication in understanding and subsequent successful operation of the future FEL light source with a highly mono-energetic LWFA beam source.

New very high resolution eight-spectral-band sensor, WorldView-2, was tested as potential source of information for soil organic carbon (SOC) mapping at field scale. The evaluation was focused firstly on the spectral resolution of the sensor and secondly on the practical application of the remotely sensed image in combination with in-situ soil spectroscopy data. The WorldView-2 sensor provides various technical improvements in the category of so-called "meter" satellites instruments. Most importantly the spectral resolution changed from typical four to eight bands covering visible (VIS) and near-infrared (NIR) wavelengths. On the other hand, the eight bands is very limited in comparison with classical hyper-spectral images to be used for soil mapping. Also the limitation of the spectral range, VIS-NIR, anticipates the potentials of the data for SOC or iron mapping. The study was conducted on arable field with area of 100 ha located in the South Moravia (Brumovice municipality). The main soil unites are Haplic Chernozem and Regosol (WRB). Field (fresh soil samples) and laboratory (dry soil samples) spectral data were extensively acquired from top soil up to 20 cm by FieldSpec-3 instrument, covering spectral range from 350 to 2500 nm. There were available 217 records with reference laboratory chemical analysis of SOC for the study. The soil spectra were further re-sampled to WorldView-2 spectral characteristics according to Relative Spectral Response Function of the sensor. Standard geometric and simplified relative atmospheric correction of the WorldView-2 image was performed. The WorlView-2 potential for SOC mapping was assessed initially by reflectance spectroscopy PLS-regression technique. The PLS inference model derived from full spectral data set applied to independent test data (10 %) showed high quality of the model: R2 = 0.92, RMSE = 0.10, and RPD = 3.5. Additionally, the same model was assessed from spectra acquired from the fresh soil samples (average gravimetric soil moisture 27.5 %) from available 100 samples. The model performed even better than the one constructed from dry samples spectra yielding R2 = 0.98, RMSE = 0.04, and RPD = 7.9. By application of the simulated WorldView-2 spectral data (eight bands) the quality of the prediction model generally decreased, however, provided still very good results highlighting the potentials. The PLSR model applied for the SOC yielded R2 = 0.76, RMSE = 0.178, and RPD = 2.1. Subsequently the WorlView-2 image spectral signatures were assessed by the reference soil sampling. Only part of the field was fully bare at the time of the image acquisition (29th April 2010). The limited data set (31 samples) was firstly tested using simulated spectra providing good model results (R2 = 0.85; RMSE = 0.15; and RPD = 2.6) and then with real WorldView-2 spectra. The PLSR performed low quality. The correlation coefficient was R2 = 0.49, RMSE = 0.29 and RPD = 1.32. Another test with WorldView-2 data was done by calculating simplified index as a slope of spectral signature in visible part of the spectra. However, this technique did not provide any good result. The initial assessment proved at first spectral potential of the WorldView-2 sensor for SOC mapping, however, the model constructed from the remotely sensed data did not confirm the potential. There exist several hypothetical reasons: the limited reference data set, the simplified pre-processing of the image and the selected modelling technique.

Dwarf-planet (1) Ceres is one of the two targets, along with (4) Vesta, that will be studied by the NASA Dawn spacecraft via imaging, visible and near-infrared spectroscopy, and gamma-ray and neutron spectroscopy. While Ceres' visible and near-infrared disk-integrated spectra have been well characterized, little has been done about quantifying spectral variations over the surface. Any spectral variation would give us insights on the geographical variation of the composition and/or the surface age. The only work so far was that of Rivkin & Volquardsen (2010, Icarus 206, 327) who reported rotationally-resolved spectroscopic (disk-integrated) observations in the 2.2-4.0 {\\mu}m range; their observations showed evidence for a relatively uniform surface. Here, we report disk-resolved observations of Ceres with SINFONI (ESO VLT) in the 1.17-1.32 {\\mu}m and 1.45-2.35 {\\mu}m wavelength ranges. The observations were made under excellent seeing conditions (0.6"), allowing us to reach a spatial resolution of ~75 km o...

Experimental results of an investigation of aqueous ammonium oxalate solutions containing Cu(II) impurity by ultraviolet-visible spectroscopy are described and discussed from the standpoint of speciation of complexes. The results show that absorption of light by aqueous ammonium oxalate solutions containing Cu(II) impurity in the range -5 < ln(c{sub i}/c) < 2.5 of the ratio of concentrations ci and c of impurity and solute, respectively, leads to decrease or increase in the intensity of bands of the ultraviolet-visible spectral regions, and these changes may be expressed by full width at half maximum, molar extinction coefficient, peak wavelength and oscillator strength. The changes are caused by the coordination of C{sub 2}O{sub 4}{sup 2-} ligand with Cu(H{sub 2}O){sub 6}{sup 2+} aquocomplex, and are related with the impurity-solute concentration ratio c{sub i}/c. The coordination of C{sub 2}O{sub 4}{sup 2-} ligand with Cu(H{sub 2}O){sub 6}{sup 2+} aquocomplex in the range 0 < ln(c{sub i}/c) < 2.5 leads to the formation of Cu(C{sub 2}O{sub 4}) complex, but the coordination of the C{sub 2}O{sub 4}{sup 2-} ligand with Cu(C{sub 2}O{sub 4}) complex in the concentration ratio range -5 < ln(c{sub i}/c) < 0 results in the formation of predominantly Cu(C{sub 2}O{sub 4}){sub 2}{sup 2-} complex. The effect of successive coordination of the C{sub 2}O{sub 4}{sup 2-} ligand is well-defined in the ultraviolet spectral region but poor in the visible region.

The photocycle of the proton acceptor complex mutant D227N of the bacterial retinal protein proteorhodopsin is investigated employing steady state pH-titration experiments in the UV-visible range as well as femtosecond-pump-probe spectroscopy and flash photolysis in the visible spectral range. The evaluation of the pH-dependent spectra showed that the neutralization of the charge at position 227 has a remarkable influence on the ground state properties of the protein. Both the pK(a) values of the primary proton acceptor and of the Schiff base are considerably decreased. Femtosecond-time-resolved measurements demonstrate that the general S(1) deactivation pathway; that is, the K-state formation is preserved in the D227N mutant. However, the pH-dependence of the reaction rate is lost by the substitution of Asp227 with an asparagine. Also no significant kinetic differences are observed upon deuteration. This is explained by the lack of a strongly hydrogen-bonded water in the vicinity of Asp97, Asp227, and the Schiff base or a change in the hydrogen bonding of it (Ikeda et al. (2007) Biochemistry 46, 5365-5373). The flash photolysis measurements prove a considerably elongated photocycle with pronounced pH-dependence. Interestingly, at pH 9 the M-state is visible until the end of the reaction cycle, leading to the conclusion that the mutation does not only lower the pK(a) of the Schiff base in the unphotolyzed ground state but also prevents an efficient reprotonation reaction. PMID:22738119

We report on the ensemble and single-molecule (SM) dynamics of Forster resonance energy transfer (FRET) in a multichromophoric rigid polyphenylenic dendrimer (triad) with spectrally different rylene chromophores featuring distinct absorption and emission spectra which cover the whole visible spectra...

On irradiation with visible light, cationic polymerization of epoxides by a photoacid generator (PAG) was sensitized by benzoquinonylsulfanyl derivatives. Spectral analyses suggest that the reduction of the quinone derivatives on irradiation was the initial and essential step of the polymerization.   

High-resolution wide field camera (WFC) that acquires high spatial ... Radar reflectivity; Visible and near-IR radiances; Cloud base and top heights; Optical depth ... A filter/polarizer wheel rotates and scans eight narrow spectral bands in the ...

Method enables use of crystal or semiconductor materials with selective spectral-response characteristics (ultraviolet, visible, or infrared wavelengths) in fabrication of contact lenses, reading glasses, and photographic processing equipment.

Computer-supported techniques are introduced in the evaluation of experimental data and obtaining the real profile of spectral lines. The direct and inverse approaches were used. The MINUIT program from the packets of CERN's library was used to solve direct problems. Tikhonov's regularization method was also applied to solve the same problems in an inverse manner. Model functions were introduced to check the applicability limitation of these methods and make a comparison between them as well. The advantages and disadvantages of these approaches were shown. The procedures were applied to the measured profiles of He II's spectral lines in a pulsed low-pressure arc. The chosen lines are He II Paschen-alpha (468.6 nm) in the visible region and Balmer-beta (121.5 nm) in the VUV spectral region. The range of experimental errors was determined where both approaches have given reliable results. It was found that we can obtain the real profile of He II 468.6 nm and He II 121.5 nm spectral lines, using the regularizati...

We obtained spectro-interferometric observations in the visible of $\\beta$~Lyrae and $\\upsilon$~Sgr using the instrument VEGA of the CHARA interferometric array. For $\\beta$~Lyrae, the dispersed fringe visibilities and differential phases were obtained in spectral regions containing the H$\\alpha$ an...

Remote sensing of the Earth has made significant progress since its inception in the 1970's. The Landsat, ASTER, MODIS multi-spectral imagers have provided a global, long-term record of the surface at visible through infrared wavelengths, and meter-scale color images can be acquired of regions of interest. However, these systems, and many of the algorithms to analyze them, have advanced surprising little over the past three decades. Very little hyperspectral data are readily available or widely used, and software analysis tools are typically complex or 'black box'. As a result it is often difficult to make quantitative assessments of surface character - for example the accurate mapping of the composition and abundance of surface components. Ironically, planetary observations often have higher spectral resolution, a broader spectral range, and global coverage, with the result that sophisticated tools are routinely applied to these data to make quantitative mineralogy maps. These analyses are driven by the reality that, except for a tiny area explored by rovers, remote sensing provides the only means to determine surface properties. Improved terrestrial hyperspectral imaging systems have long been proposed, and will make great advances. However, these systems remain in the future, and the question exists - what advancements can be made to extract quantitative information from existing data? A case study, inspired by the 1987 work of Sultan et al, was performed to combine all available visible, near-, and thermal-IR multi-spectral data with selected hyperspectral information and limited field verification. Hyperspectral data were obtained from lab observations of collected samples, and the highest spatial resolution images available were used to help interpret the lower-resolution regional imagery. The hyperspectral data were spectrally deconvolved, giving quantitative mineral abundances accurate to 5-10%. These spectra were degraded to the multi-spectral resolution and deconvolved with a similarly degraded and reduced spectral library, whose endmember selection was informed by the hyperspectral results. Using these carefully chosen endmembers, the deconvolved spectra provide results that are similar to the hyperspectral analysis in many, but not all cases; future work is needed to understand exactly why and when. Analysis of high-spectral-resolution data reveals that the subtle spectral variations present in the multi-spectral data represent true variations in surface composition. Nine distinct compositional units can be identified, with subtle composition variations within these units that are confirmed by analysis of spectra of collected samples and field inspection. This compositional mapping is accurate enough to confidently map the details of the highly complex, structurally rotated and thrusted terrain of the Granite Wash Mtns, Arizona. This work illustrates that even a limited amount of high spectral and spatial resolution data provide extremely powerful tools to extend the analysis of the satellite multi-spectral data, significantly increasing the accuracy of, and confidence in, the use of these data for quantitative compositional mapping. Until hyperspectral remote sensing systems become available, these approaches provide a means to meaningfully expand the utility and use of existing multi-spectral data.

We present an update of the visible and near-infrared colour database of Minor Bodies in the Outer Solar System (MBOSSes), which now includes over 2000 measurement epochs of 555 objects, extracted from over 100 articles. The list is fairly complete as of December 2011. The database is now large enough to enable any dataset with a large dispersion to be safely identified and rejected from the analysis. The selection method used is quite insensitive to individual outliers. Most of the rejected datasets were observed during the early days of MBOSS photometry. The individual measurements are combined in a way that avoids possible rotational artifacts. The spectral gradient over the visible range is derived from the colours, as well as the R absolute magnitude M(1,1). The average colours, absolute magnitude, and spectral gradient are listed for each object, as well as the physico-dynamical classes using a classification adapted from Gladman and collaborators. Colour-colour diagrams, histograms, and various other plots are presented to illustrate and investigate class characteristics and trends with other parameters, whose significances are evaluated using standard statistical tests. Except for a small discrepancy for the J-H colour, the largest objects, with M(1,1) < 5, are indistinguishable from the smaller ones. The larger ones are slightly bluer than the smaller ones in J-H. Short-period comets, Plutinos and other resonant objects, hot classical disk objects, scattered disk objects and detached disk objects have similar properties in the visible, while the cold classical disk objects and the Jupiter Trojans form two separate groups of their spectral properties in the visible wavelength range. The well-known colour bimodality of Centaurs is confirmed. The hot classical disk objects with large inclinations, or large orbital excitations are found to be bluer than the others, confirming a previously known result. Additionally, the hot classical disk objects with a smaller perihelion distance are bluer than those that do not come as close to the Sun. The bluer hot classical disk objects and resonant objects have fainter absolute magnitudes than the redder ones of the same class. Finally, we discuss possible scenarios for the origin of the colour diversity observed in MBOSSes, i.e. colouration caused by evolutionary or formation processes. The colour tables and all plots are also available on the MBOSS colour web page, which will be updated when new measurements are published Full Tables 2 and 3 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A115

Polar mesospheric clouds (PMC), also called noctilucent clouds, are the visible manisfestation of icy particles persistently present in the polar summer mesopause region. Their formation is a rather complicated physical process depending on atmospheric backgroud parameters, such as temperature and water vapor. These parameters are highly variable and hardly to measure directly at such altitudes. These clouds, located at the edge of space, have been recently studied with GOMOS on ENVISAT. GOMOS is a stellar occultation instrument combining 4 spectrometers in the spectral range 250 to 950 nm (UV - visible - near IR) and 2 fast photometers (470-520 nm and 650-700 nm). On the day side, in addition to starlight, GOMOS measures the sunlight scattered from the Earth’s limb. In the summer polar day, polar mesospheric clouds are clearly detected using the photometers signals. The sun-synchronous orbit of ENVISAT allows observing them in both hemispheres. The observation of these clouds with the spectrometers provides the spectral dependence of the scattering by PMC particles from which it is possible to derive particle radii. After a brief overview of GOMOS PMC data set, the retrieval method will be explained and results from several PMC seasons will be described, as well as their temporal and latitudinal variations. This work takes part in a working group, the Particle Size Working Group, which includes representatives from the different experiments observing PMC particles, and whose goal is to determine the state-of-the-art in mesospheric ice particle size.

The laser thermal melting of powders is used to fabricate selective emitters (SEs) that represent Nd2O3 and Y2O3-Nd2O3 polycrystals on quartz holders. The SEs are stable under atmospheric conditions upon multiple heating by laser radiation up to the melting point. The spectral shape and integral intensity of the selective heat radiation (SHR) of the Nd2O3 microcrystalline powder and the Nd2O3 and Y2O3-Nd2O3 polycrystals are experimentally studied in the near-IR and visible spectral ranges versus the intensity of the laser thermal excitation at a wavelength of 10.6 ?m in comparison with the absorption and luminescence spectra of the YAG:Nd3+ and YAlO3:Nd3+ single crystals. The SHR spectra are determined by the vibronic transitions between the electronic states 2 G 7/2-4F3/2 4I11/2 and 4I9/2 of the Nd3+ ions that are thermally excited due to the multiphonon transitions from the ground state. The energy balance of the SE laser thermal heating is experimentally investigated. The coefficient of the laser energy conversion to the Nd3+ SHR is measured, and the emissivity of the SEs that can be used for the study of the thermophotovoltaic generators and the optical excitation of the laser-active media in the near-IR spectral range is estimated.

Arrays of metal nanowires represent uniaxial metamaterials, whose principal effective permittivities perpendicular and parallel to the wire axis have opposite sign in the infrared and visible spectral range. This property leads to a hyperbolic equi-frequency surface for the extraordinary rays in wave vector space allowing the propagation of waves with unusually large wave vectors. Here we present an experimental mapping of the hyperbolic equi-frequency surfaces of TM (p-)polarised light propagating within a silver nanowire array. To this purpose we performed angular resolved transmission measurements on a 1.7 micron high alumina film containing the silver nanowire array. From the order of the observed Fabry-Perot resonances the wave vector component k{sub z} is determined, while the lateral wave vector component k{sub x}, is obtained from the angle of incidence. The resulting markings in k{sub x}-k{sub z} wave vector diagram then result in a hyperbolic equi-frequency surface for the TM polarisation. Fitting the relationship between spectral position of the Fabry-Perot peaks and angle of incidence by a simple linear equation, we furthermore determined the values of the principal permittivities for TE and TM polarisation in a wide spectral range. All experimental results agree well with simulations based on the Maxwell-Garnett effective medium theory.

Asteroid 162173 (1999JU3; hereafter JU3) is the target of the Hayabusa-2 mission. Its visible reflectance spectra have been observed a few times [1,2], and obtained spectra exhibit a wide variety of spectral patterns ranging from a spectra with absorption in the UV region (May 1999) to a flat spectrum with a faint broad absorption centered around 0.6 microns (September 2007) and that with UV absorption and strong broad absorption centered around 0.7 micron (July 2007). The apparent large spectral variation may be due to variegation on the asteroid surface. Such variegation would make a large influence on remote sensing strategy for Hayabusa-2 before its sampling operations. In order to better constraint the spectral properties of JU3, we conducted visible spectroscopic observations at the GEMINI-South observatory 8.1-m telescope with the GMOS instrument. We could obtain three different sets of data in June and July 2012. Although the JU3 rotation phases of two of the observation are close to each other, the other is about 120 degrees away from the two. Our preliminary analyses indicate that these three spectra are slightly reddish but generally flat across the observed wavelength range (0.47 - 0.89 microns). The observed flat spectra are most similar to the spectrum obtained in September 2007, which probably has the highest signal-to-noise ratio among the previous three spectra. This result suggests that material with a flat spectrum probably covers a dominant proportion of the JU3 surface and that the other two types of previously obtained spectra may not cover a very large fraction of the JU3 surface. [1] Binzel, R. P. et al. (2001) Icarus, 151, 139-149; [2] Vilas, F. (2008) AJ, 135, 1101-1105.

The Multi-Spectral Solar Telescope Array (MSSTA) is a sounding rocket-borne observatory composed of a set of normal-incidence multilayer-coated telescopes that obtained selected bandpass spectroheliograms (44 to 1550 angstroms) of the solar atmosphere. These spectroheliograms were recorded on specially fabricated XUV And FUV 70-mm Kodak film. Rocket launches of this instrument payload took place in 1991 (MSSTA I) and 1994 (MSSTA II) at the White Sands Missile Test Range in New Mexico, sponsored by the National Aeronautics and Space Administration (NASA) sounding rocket experiment program. Immediately prior to the 1994 launch, visible light focusing tests of each telescope were performed in situ using a 1951 standard Air Force high- resolution test target, to measure optical resolution performance. We determined that the MSSTA II telescopes performed at diffraction-limited resolutions down to 0.70 arcsec at visible wavelengths. Based on these measurements, we calculate an upper bound to the focusing errors that incorporate the sum of all uncorrelated system focus errors that affect resolution performance. Coupling these upper bound estimates with the in-band diffraction limits, surface scattering errors and payload pointing jitter, we demonstrate that 11 of 19 MSSTA II telescopes--having negligible figures of focus errors in comparison to the corresponding visible diffraction limits--performed at sub arcsecond resolution at their operational FUV/EUV/XUV wavelengths during flight. We estimate the in-band performance down to 0.14 +/- 0.08 arcsec.

Matter structured on a length scale comparable to or smaller than the wavelength of light can exhibit unusual optical properties. Particularly promising components for such materials are metal nanostructures, where structural alterations provide a straightforward means of tailoring their surface plasmon resonances and hence their interaction with light. But the top-down fabrication of plasmonic materials with controlled optical responses in the visible spectral range remains challenging, because lithographic methods are limited in resolution and in their ability to generate genuinely three-dimensional architectures. Molecular self-assembly provides an alternative bottom-up fabrication route not restricted by these limitations, and DNA- and peptide-directed assembly have proved to be viable methods for the controlled arrangement of metal nanoparticles in complex and also chiral geometries. Here we show that DNA origami enables the high-yield production of plasmonic structures that contain nanoparticles arranged in nanometre-scale helices. We find, in agreement with theoretical predictions, that the structures in solution exhibit defined circular dichroism and optical rotatory dispersion effects at visible wavelengths that originate from the collective plasmon-plasmon interactions of the nanoparticles positioned with an accuracy better than two nanometres. Circular dichroism effects in the visible part of the spectrum have been achieved by exploiting the chiral morphology of organic molecules and the plasmonic properties of nanoparticles, or even without precise control over the spatial configuration of the nanoparticles. In contrast, the optical response of our nanoparticle assemblies is rationally designed and tunable in handedness, colour and intensity-in accordance with our theoretical model. PMID:22422265

Elastic light scattering spectroscopy (ESS) has the potential to provide spectra that contain both morphological and chromophore information from tissue. We report on a preliminary study of this technique, with the hope of developing a method for diagnosis of highly-pigmented skin lesions, commonly associated with skin cancer. Four opossums were treated with dimethylbenz(a)anthracene to induce both malignant melanoma and benign pigmented lesions. Skin lesions were examined in vivo using both UV-visible and near infrared (NIR) ESS, with wavelength ranges of 330-900 nm and 900-1700 nm, respectively. Both portable systems used identical fiber-optic probe geometry throughout all of the measurements. The core diameters for illuminating and collecting fibers were 400 and 200 {micro}m, respectively, with center-to-center separation of 350 {micro}m. The probe was placed in optical contact with the tissue under investigation. Biopsies from lesions were analyzed by two standard histopathological procedures. Taking into account only the biopsied lesions, UV-visible ESS showed distinct spectral correlation for 11/13 lesions. The NIR-ESS correlated well with 12/13 lesions correctly. The results of these experiments showed that UV-visible and NIR-ESS have the potential to classify benign and malignant skin lesions, with encouraging agreement to that provided by standard histopathological examination. These initial results show potential for ESS based diagnosis of pigmented skin lesions, but further trials are required in order to substantiate the technique.

A wide observational campaign was carried out in 2004-2009 aimed to complete the ground-based investigation of Lutetia prior to the Rosetta fly-by in July 2010. We have obtained BVRI photometric and V-band polarimetric measurements over a wide range of phase angles, and visible and infrared spectra in the 0.4-2.4 micron range. We analyzed them together with previously published data to retrieve information on Lutetia's surface properties. Values of lightcurve amplitudes, absolute magnitude, opposition effect, phase coefficient and BVRI colors of Lutetia surface seen at near pole-on aspect have been determined. We defined more precisely parameters of polarization phase curve and showed their distinct deviation from any other moderate-albedo asteroid. An indication of possible variations both in polarization and spectral data across the asteroid surface was found. To explain features found by different techniques we propose that (i) Lutetia has a non-convex shape, probably due to the presence of a large crater,...

Over the last few decades, General Circulation Models (GCM) have been used to simulate the current martian climate. The calibration of these GCMs with the current seasonal cycle is a crucial step in understanding the climate history of Mars. One of the main climatic signals currently used to validate GCMs is the annual atmospheric pressure cycle. It is difficult to use changes in seasonal deposits on the surface of Mars to calibrate the GCMs given the spectral ambiguities between CO2 and H2O ice in the visible range. With the OMEGA imaging spectrometer covering the near infra-red range, it is now possible to monitor both types of ice at a spatial resolution of about 1 km. At global scale, we determine the change with time of the Seasonal South Polar Cap (SSPC) crocus line, defining the edg...

The possibility to use Tb3+ as luminescence sensitizer for enhancement of the conversion efficiency of vacuum-ultraviolet (VUV) radiation into visible light was examined. We studied the luminescence properties of K3Tb(PO4)2 and Ba3Tb(PO4)3 activated by Eu3+, and of SrAl12O19 co-doped with Mn2+ and Tb3+ at excitation over the 120 to 300 nm wavelength range. It is shown that Tb3+ ions, exhibiting a strong absorption band in the VUV, can provide efficient sensitization of Eu3+ and Mn2+ emissions for excitation in this spectral range, giving rise to intense red and green luminescence, respectively. This study provides a proof for the concept of VUV sensitization, which enables the engineering of luminescence materials with improved efficiency for excitation from a noble gas discharge.

We present the spatial distribution of air temperature on Venus' night side, as observed by the high spectral resolution channel of VIRTIS (Visible and Infrared Thermal Imaging Spectrometer), or VIRTIS-H, on board the ESA mission Venus Express. The present work extends the investigation of the average thermal fields in the northern hemisphere of Venus, by including the VIRTIS-H data. We show results in the pressure range of 100-4mbar, which corresponds to the altitude range of 65-80km. With these new retrievals, we are able to compare the thermal structure of the Venus' mesosphere in both hemispheres. The major thermal features reported in previous investigations, i.e. the cold collar at about 65-70degreeS latitude, 100mbar pressure level, and the asymmetry between the evening and morning ...

In the context of the conceptual design study for the European Solar Telescope (EST) we have investigated different metallic mirror coatings in terms of reflectivity, polarization properties and durability. Samples of the following coating types have been studied: bare aluminum, silver with different dielectric layers for protection and UV enhancement, and an aluminum-silver combination. From 2009 to 2011 we have carried out a long-term durability test under realistic observing conditions at the VTT solar telescope of the Observatorio del Teide (Tenerife, Spain), accompanied by repeated reflectivity measurements in the EST spectral working range (0.3 - 20 ?m), and by polarization measurements in the visible range. The test results allow us to find the optimum coatings for the different mirrors in the EST beampath and to eventually assess aging effects and re-coating cycles. The results of the polarization measurements are a valuable input for an EST telescope polarization model, helping to meet the stringent requirements on polarimetric accuracy.

In this paper the concept of a microspectrometer based on a Linear Variable Optical Filter (LVOF) for operation in the visible spectrum is presented and used in two different designs: the first is for the narrow spectral band between 610 nm and 680 nm, whereas the other is for the wider spectral ban...

In this study, the potential of visible and near-infrared spectral imaging as a technique of document inspection was examined. Doubtful documents are often found in economic cases, distinguished between original and added strokes and detected blurry characters are very useful for judgment. Burned, covered and rinsed documents in which the characters can't be identified with naked eyes were experimentally studied with a visible spectral imaging technique. Meanwhile, the same color inks were detected by both visible and near-infrared imaging spectrometers. Classification of spectral images was carried out in specialist spectral imaging software packager Misystem provided by Institute of Forensic Science. The technique significantly improved the detection of many documents, especially those that might be considered of poor quality or borderline characters. The visible spectral imaging was successful in detecting the burnt Chinese characters produced using pencils. It was possible to form spectral images showing the strokes even covered by Chinese ink by means of imaging at characteristic frequencies. As inks have very different spectral from the clothes, contribution and contrast of the rinsed lines and illegible seal words on clothes were clearly enhanced. By examining the spectral images from the inks, it was possible to determine whether the same color inks were written by the different pens. The results also show that the near-infrared spectrometer is better than visible one in distinguishing the same inks. In blind testing, spectral imaging was shown to achieve an average 85.1% chance of success. The results reveal the wide applications of spectral imaging in document evidence analysis. The potential of this technique in forensic science will be more apparent along with the further and deeper studies.

Rosetta, part of ESA's Horizon 2000 programme, will orbit and land on the comet 67P/Churyumov-Gerasimenko in May 2014. However, launched in March 2004, its trajectory has thus far muchly consisted of a series of planetary fly-bys and gravitational assists using Mars (2007) and Earth (March 2005, 2007 and 2009). During these close fly-bys Rosetta captured measurements of these planets - and of particular interest are those registed by the Visual Infrared Thermal Imaging Spectrometer VIRTIS of Earth, which were taken to help calibrate VIRTIS. Rosetta/VIRTIS measures at high spectral resolution from 0.25 - 5.0 microns, a spectral range which has been well studied by Earth observing instruments such as Meteosat Second Generation Spinning Enhanced Visible and Infrared Imager (MSG/SEVIRI) and the Advanced Along-Track Scanning Radiometer (AATSR). Earth observing instruments, whilst having superior spatio-temporal coverage to the data provided during the Rosetta/VIRTIS fly-bys, are typically constrained to measuring in only a few spectral channels. Hence, Rosetta/VIRTIS should yield more detailed spectral information than these instruments - and is a good candidate for intercomparison studies. To this end, the radiative transfer software NEMESIS (Irwin et al., 2009) is employed for the first time on Earth simulations, having been used extensively for other bodies such as Venus, Mars, Jupiter, Saturn, Neptune, Uranus and Titan. This work compares Rosetta/VIRTIS measurements with NEMESIS-simulated spectra, concentrating on quantifying the ability of NEMESIS to reproduce spectral features associated with different surface topographies (such as ocean, desert and vegetation) in combination with clear and cloudy atmospheric states. Preliminary estimations of temperature and trace-species concentrations and distributions are presented as sample products.

The central problem of temperature-emissivity separation is that we obtain N spectral measurements of radiance and need to find N + 1 unknowns (N emissivities and one temperature). To solve this problem in the presence of the atmosphere we need to find even more unknowns: N spectral transmissions {tau}{sub atmo}({lambda}) up-welling path radiances L{sub path}{up_arrow}({lambda}) and N down-welling path radiances L{sub path}{down_arrow}({lambda}). Fortunately there are radiative transfer codes such as MODTRAN 3 and FASCODE available to get good estimates of {tau}{sub atmo}({lambda}), L{sub path}{up_arrow}({lambda}) and L{sub path}{down_arrow}({lambda}) in the order of a few percent. With the growing use of hyperspectral imagers, e.g. AVIRIS in the visible and short-wave infrared there is hope of using such instruments in the mid-wave and thermal IR (TIR) some day. We believe that this will enable us to get around using the present temperature - emissivity separation (TES) algorithms using methods which take advantage of the many channels available in hyperspectral imagers. The first idea we had is to take advantage of the simple fact that a typical surface emissivity spectrum is rather smooth compared to spectral features introduced by the atmosphere. Thus iterative solution techniques can be devised which retrieve emissivity spectra {epsilon} based on spectral smoothness. To make the emissivities realistic, atmospheric parameters are varied using approximations, look-up tables derived from a radiative transfer code and spectral libraries. By varying the surface temperature over a small range a series of emissivity spectra are calculated. The one with the smoothest characteristic is chosen. The algorithm was tested on synthetic data using MODTRAN and the Salisbury emissivity database.

The emergence of spectrally multimode smart missiles requires hardware-in-the-loop (HWIL) facilities to simulate multiple spectral signatures simultaneously. While traditional diode-pumped solid-state (DPSS) sources provide a great basic testing source for smart missiles, they typically are bulky and provide substantially more power peak power than what is required for laboratory simulation, have fixed pulse widths, and require some external means to attenuate the output power. HWIL facilities require systems capable of high speed variability of the angular divergence and optical intensity over several orders of magnitude, which is not typically provided by basic DPSS systems. In order to meet the needs of HWIL facilities, we present a low-cost semi-active laser (SAL) simulator source using laser diode sources that emits laser light at the critical wavelengths of 1064 nm and 1550 nm, along with light in the visible for alignment, from a single fiber aperture. Fiber delivery of the multi-spectral output can provide several advantages depending on the testing setup. The SAL simulator source presented is capable of providing attenuation of greater than 70 dB with a response time of a few milliseconds and provides a means to change the angular divergence over an entire dynamic range of 0.02- 6º in less than 400 ms. Further, the SAL simulator is pulse width and pulse repetition rate agile making it capable of producing both current and any future coding format necessary.

This paper presents a comparison of dimension reduction methods based on a novel machine vision application for estimating moisture content in sand used to make concrete. For the application in question it is very important to know the moisture content of the sand so as to ensure good-quality concrete. In order to achieve a continuous in-line approach for the concrete mixing, digital image analysis is used. Multi-spectral images, consisting of nine spectral bands in the visible and near infrared (NIR) range, were acquired. Each image consists of approximately 9 million pixels. Five different sand types were examined with 20-60 images for each type. To reduce the amount of data, features were extracted from the multi-spectral images; the features were summary statistics on single bands and pairs of bands as well as morphological summaries. The number of features (2,016) is high in relation to the number of observations and, therefore, dimension reductive methods are needed. Furthermore, speed, which is an important consideration, is aided by the use of a small number of variables. On top of that, fewer dimensions tend to give more robust results. Two traditional statistical methods for dimension reduction (forward selection and principal components) combined with ordinary least squares and one sophisticated chemometrics algorithm (genetic algorithm-partial least squares) are compared to the recently proposed least angle regression-elastic net (LARS-EN) model selection method.

Visible and near-IR (VNIR) spectra of both Martian bright and dark regions are characterized by a ferric absorption edge extending from approx. 400 to 750 nm, with bright regions having about twice the reflectivity at 750 nm as dark regions. Between 750 nm to beyond 2000 nm, bright and dark regions have nearly constant and slightly negative spectral slopes, respectively. Depending on location, bright regions have shallow reflectivity minima in the range 850-910 nm that are attributed to ferric oxides. Similarly, dark regions have shallow reflectivity minima near approx. 950 and 1700-2000 nm that are attributed to ferrous silicate minerals (pyroxene). Among terrestrial geologic materials, the best spectral analogues for Martian bright regions are certain palagonitic tephras from Mauna Kea Volcano (Hawaii). By definition, palagonite is a "yellow or orange isotropic mineraloid formed by hydration and devitrification of basaltic glass". The ferric pigment in palagonite is nanometer-sized ferric oxide particles (np-Ox) dispersed throughout the hydrated basaltic glass matrix. The hydration state of the np-Ox particles is not known, but the best Martian spectral analogues contain allophane-like materials and not crystalline phyllosilicates.

High pressure high temperature CO adsorption and coadsorption with ethylene and propylene on Pt(111) was monitored in situ with infrared-visible sum frequency generation (SFG). At high pressures and high temperatures, CO dissociates on a Pt(111) surface to form carbon. At 400 torr CO pressure and 673K, CO modifies the Pt(111) surface through a carbonyl intermediate, and dissociates to leave carbon on the surface. SFG was used to follow the CO peak evolution from monolayer adsorption in ultra high vacuum (UHV) to 400 torr CO pressure. At this high pressure, a temperature dependence study from room temperature to 823K was carried out. Auger electron spectroscopy was used to identify carbon on the surface CO coadsorption with ethylene and CO coadsorption with propylene studies were carried out with 2-IR 1-visible SFG. With this setup, two spectral ranges covering the C-H stretch range and the CO stretch range can be monitored simultaneously. The coadsorption study with ethylene reveals that after 5L ethylene exposure on a Pt(111) surface to form ethylidyne , CO at high pressures cannot completely displace the ethylidyne from the surface. Instead, CO first adsorbs on defect sites at low pressures and then competes with ethylidyne for terrace sites at high pressures. Propylene coadsorption with CO at similar conditions shows that propylidyne undergoes conformation changes with increased CO pressure and at 1 torr, is absent from the Pt(111) surface. Experiments on CO poisoning of ethylene hydrogenation was carried by 2-IR 1-visible SFG. At 1 torr CO,10 torr ethylene and 100 torr hydrogen, CO was found to block active sites necessary for ethylene hydrogenation, Above 425K, CO desorbs from the surface to allow ethylene hydrogenation to occur. The gas phase species were monitored by gas chromatography.

We have analysed the XMM-Newton spectra of SS 433 using a standard model of adiabatically and radiatively cooling X-ray jets. The multi-temperature thermal jet model reproduces well the strongest observed emission line fluxes. The thermal model alone can not reproduce the continuum radiation in the XMM spectral range, the fluorescent iron line and some broad spectral features. Using the thermal jet-plus-reflection model, we find a notable contribution of ionized reflection to the spectrum in the energy range from ~3 to 12 keV. The reflecting surface is highly ionized (xi ~300), the illuminating radiation spectrum is flat and probably strongly absorbed. We conclude that the reflected spectrum is an evidence of the supercritical disc funnel, where the illuminating radiation comes from deeper funnel regions, to be further reflected in the outer visible funnel walls (r >~2*10^11 cm). We have not found any evidences of reflection in the soft 0.8-2 keV energy range, instead, a soft excess is detected, that does not...

Context: IRC +10420 is a massive evolved star belonging to the group of yellow hypergiants. Currently, this star is rapidly evolving through the Hertzprung-Russell diagram, crossing the so-called yellow void. IRC +10420 is suffering from intensive mass loss which led to the formation of an extended dust shell. Moreover, the dense stellar wind of IRC +10420 is subject to strong line emission. Aims: Our goal was to probe the photosphere and the innermost circumstellar environment of IRC +10420, to measure the size of its continuum- as well as the Br? line-emitting region on milliarcsecond scales, and to search for evidence of an asymmetric distribution of IRC +10420's dense, circumstellar gas. Methods: We obtained near-infrared long-baseline interferometry of IRC +10420 with the AMBER instrument of ESO's Very Large Telescope Interferometer (VLTI). The measurements were carried out in May/June 2007 and May 2008 in low-spectral resolution mode in the JHK bands using three auxillary telescopes (ATs) at projected baselines ranging from 30 to 96 m, and in October 2008 in high-spectral resolution mode in the K band around the Br? emission line using three unit telescopes (UTs) with projected baselines between 54 and 129 m. The high-spectral resolution mode observations were analyzed by means of radiative transfer modeling using CMFGEN and the 2D Busche & Hillier codes. Results: For the first time, we have been able to absolutely calibrate the H- and K-band data and, thus, to determine the angular size of IRC+10420's continuum- and Br? line-emitting regions. We found that both the low resolution differential and closure phases are zero within the uncertainty limits across all three bands. In the high-spectral resolution observations, the visibilities show a noticeable drop across the Br? line on all three baselines. We found differential phases up to -25° in the redshifted part of the Br? line and a non-zero closure phase close to the line center. The calibrated visibilities were corrected for AMBER's limited field-of-view to appropriately account for the flux contribution of IRC +10420's extended dust shell. From our low-spectral resolution AMBER data we derived FWHM Gaussian sizes of 1.05±0.07 and 0.98±0.10 mas for IRC +10420's continuum-emitting region in the H and K bands, respectively. From the high-spectral resolution data, we obtained a FWHM Gaussian size of 1.014±0.010 mas in the K-band continuum. The Br? -emitting region can be fitted with a geometric ring model with a diameter of 4.18^+0.19-0.09 mas, which is approximately 4 times the stellar size. The geometric model also provides some evidence that the Br? line-emitting region is elongated towards a position angle of 36°, well aligned with the symmetry axis of the outer reflection nebula. Assuming an unclumped wind and a luminosity of 6×10^5{ {L}&sun;}, the spherical radiative transfer modeling with CMGFEN yields a current mass-loss rate of 1.5-2.0×10-5{ {M}&sun; yr-1} based on the Br? equivalent width. However, the spherical CMFGEN model poorly reproduces the observed line shape, blueshift, and extension, definitively showing that the IRC +10420 outflow is asymmetric. Our 2D radiative transfer modeling shows that the blueshifted Br? emission and the shape of the visibility across the emission line can be explained with an asymmetric bipolar outflow with a high density contrast from pole to equator (8-16), where the redshifted light is substantially diminished. The low-spectral resolution data have been obtained as part of the Guaranteed Time Programme for VLTI/AMBER (program ID: 079.D-0356(B)), while the high-spectral resolution data were obtained in the context of science verification observations (program ID: 60.A-9053(D)).

Ozone is a radiativelly and chemically important trace gas in the atmosphere. Accurate monitoring of ozone vertical distributions is crucial for a better understanding of air quality and climate change. The Geostationary Coastal and Air Pollution Events (GEO-CAPE) mission, an Earth Science Decadal Survey mission that has been recommended for launch in the 2013-2016 time frame by National Research Council, will measure tropospheric ozone and its precursors relating to air quality over the Americas. To improve current capability of tropospheric ozone sounding in terms of spatial and temporal resolution, GEO-CAPE mission calls for an instrument(s) that is sensitive over multiple spectral regions. Prior to the launch of GEO-CAPE satellite, using simultaneous measurements of multiple sensors of an ongoing satellite mission provide an alternative way to improve tropospheric ozone sounding and help in the evaluations of suitable spectral regions for the GEO-CAPE mission. The Ozone Monitoring Instrument (OMI) and the Tropospheric Emission Spectrometer (TES) are both on the Earth Observing System Aura satellite in orbit. They are providing ozone concentration profiles measurements respectively. OMI is a nadir-viewing pushbroom ultraviolet-visible (UV-VIS) imaging spectrograph that measures backscattered radiances covering the 270-500 nm wavelength range. TES is a Fourier transform spectrometer that measures the thermal infrared (TIR) light radiances emitted by Earth's surface and by gases and particles in spectral range 650 - 3050 cm-1. We present an approach to combine simultaneously measured OMI UV and TES TIR radiances to improve the tropospheric ozone sounding. The results from combination of these measurements are presented and discussed. The improvements on tropospheric ozone profiles from the UV+TIR joint retrievals, as compared with either spectral region alone, are charterized using the ozonesonde measurements.

Positively charged porphyrins bearing an acridine with various lengths of diamino alkyl linkage, 5-[4-[(6-chloro-2-methoxy-9-acridyl)aminoalkylaminocarbonyl]phenyl]-10, 15, 20-tris(4-N-methylpyridiniumyl)porphine triiodide, alkyl=ethyl, butyl, hexyl, or octyl, were synthesized. They exhibited more enhanced photocleavage activity of pUC18 plasmid DNA than TMPyP, meso-tetrakis(4-N-methylpyridiniumyl)porphine, which is well known to bind to DNA tightly and to cleave DNA effectively; the hybrid linked with the hexamethylene chain showed particularly high activity. An equilibrium dialysis experiment demonstrated that the binding ability of the hybrids to calf thymus (CT) DNA correlated quantitatively with the photocleavage activity. The lack of the substantial red-shift of the Soret maxima of the hybrids through the titration with CTDNA denied the intercalative binding of the porphyrin part. In their circular dichroism (CD) spectral change on binding to CTDNA, two negative peaks appeared at 275 nm and at 285-290 nm in the UV range. The latter negative peak was observed for hybrids, but not for TMPyP, and thus we assigned it to induced CD (ICD) derived from intercalation of acridine chromophore. In the visible range, the hybrids showed only a positive peak around their Soret maxima, and this feature suggested the porphyrin moiety lay in the DNA groove. In addition, the length of the linker markedly influenced the ellipticity of their visible ICD, suggesting that the proximity of the porphyrin moiety to DNA was greatly affected by the linker.   

A transparent porous anodized aluminum oxide (AAO) nanostructure was formed on a glass substrate using the anodization of a highly pure evaporated aluminum layer. A parametric study was carried out in order to achieve a fine control of the microstructural and optical properties of the elaborated films. The microstructural and surface morphologies of the porous alumina films were characterized by x-ray diffraction and atomic force microscopy. Pore diameter, inter-pore separation, and the porous structure as a function of anodization conditions were investigated. It was then found that the pores density decreases with increasing the anodization time. Regular cylindrical porous AAO films with a flat bottom structure were formed by chemical etching and anodization. A high transmittance in the 300-900 nm range is reported, indicating a fulfilled growth of the transparent sample (alumina) from the aluminum metal. The data showed typical interference oscillations as a result of the transparent characteristics of the film throughout the visible spectral range. The thickness and the optical constants (n and k) of the porous anodic alumina films, as a function of anodizing time, were obtained using spectroscopic ellipsometry in the ultraviolet-visible-near infrared (UV-vis-NIR) regions.

The electronic energy transfer properties between Ho3+ and Yb3+ ions have been studied in a fluoroindate glass for solar cell applications. The Ho3+ ions absorb infrared radiation at around 1150nm, below the energy gap of Si solar cells. Energy transfer between Ho3+ and Yb3+ ions produces an upconversion emission in the visible and in the near infrared spectral range just above the Si bandgap. When these glasses are placed at the rear of a bifacial Si solar cell, the upconverted radiation can be absorbed by Si and generate electron–hole pairs that contribute to enhance the cell efficiency. An estimation of the expected increase in photo-current has been calculated when the upconverter material is used in a solar concentrator. Besides, they ca...

The airborne laser scanning LIDAR (LIght Detection And Ranging) provides high-resolution Digital Terrain Models (DTM) that have been applied recently to the characterization, quantification and monitoring of coastal environments. This study assesses the contribution of LIDAR altimetry and intensity data, topographically-derived features (slope and aspect), and multi-spectral imagery (three visible and a near-infrared band), to map coastal habitats in the Bidasoa estuary and its adjacent coastal area (Basque Country, northern Spain). The performance of high-resolution data sources was individually and jointly tested, with the maximum likelihood algorithm classifier in a rocky shore and a wetland zone; thus, including some of the most extended Cantabrian Sea littoral habitats, within the Bay...

The glasses of the composition 19Na2SO4-20MO-60P2O5: 1.0Ho2O3/1.0Er2O3 (M=Mg, Ca, and Ba) have been synthesized. Optical absorption and fluorescence spectra (in the spectral range 350-2100nm were studied at ambient temperature. The spectra were characterized using Judd-Ofelt theory. From the luminescence spectra, various radiative properties like transition probability A, branching ratio b and the radiative life time t for blue (B), green (G) and red emission levels of these glasses have been evaluated. The energy transfer between the two rare earth ions (Ho^3^+ and Er^3^+) in co-doped Na2SO4-MO-P2O5 glass systems in the visible and NIR regions has also been investigated. Highest intensity, the highest quantum efficiency and maximum energy transfer with low phonon losses of B, G, and R lin...

Results of experiments on the deposition of multilayer low-emission coatings with ?oxide-metaloxide? structure on polyethylene terephthalate film by magnetron sputtering are presented. The purpose of this work was to find the composition of coatings which would have high moisture resistance and the possibility to operate outside sealed glass units. For this purpose, coatings with TiO2/ZnO:Ga/Ag/ZnO:Ga/TiO2 and TiO2/Cu/TiO2 structures were proposed and their optical and electrical characteristics were investigated. The optimum thickness of coating layers which provides a good ratio of coating transparency in the visible range with reflection in infrared spectral region was obtained. It was shown that low-emission coatings based on a Ag layer have a higher transparency (82%) and reflection i...

The experimental data on the transient optical absorption of wide-band-gap optical crystals of lithium borates Li2B4O7, LiB3O5, and Li6Gd(BO3)3 and potassium (KH2PO4 (KDP)) and ammonium (NH4H2PO4 (ADP)) dihydrogen phosphates in the visible and ultraviolet spectral regions are analyzed using the theory of diffusion-controlled tunneling recombination. A nanosecond pulsed radiation action on these crystals is shown to form defect pairs, such as polaron-type hole centers and electron centers based on interstitial cations. The relaxation kinetics of these centers over a wide time range of 10?8?10 s is described by a proposed model of tunneling electron transfer between antimorphous defects in the cation sublattice under the thermally stimulated mobility of recombination partners. The numerical ...

Robust control and stabilization of optical frequency combs enables an extraordinary range of scientific and technological applications, including frequency metrology at extreme levels of precision, novel spectroscopy of quantum gases and of molecules from visible wavelengths to the far infrared, searches for exoplanets, and photonic waveform synthesis. Here we report on the stabilization of a microresonator-based optical comb (microcomb) by way of mechanical actuation. This represents an important step in the development of microcomb technology, which offers a pathway toward fully-integrated comb systems. Residual fluctuations of our 32.6 GHz microcomb line spacing reach a record stability level of $5\\times10^{-15}$ for 1 s averaging, thereby highlighting the potential of microcombs to support modern optical frequency standards. Furthermore, measurements of the line spacing with respect to an independent frequency reference reveal the effective stabilization of different spectral slices of the comb with a $&...

Solar observations at sub-THz frequencies detected a new flare spectral component peaking in the THz range, simultaneously with the well known microwaves component, bringing challenging constraints for interpretation. Higher THz frequencies observations are needed to understand the nature of the mechanisms occurring in flares. A THz photometer system was developed to observe outside the terrestrial atmosphere on stratospheric balloons or satellites, or at exceptionally transparent ground stations. The telescope was designed to observe the whole solar disk detecting small relative changes in input temperature caused by flares at localized positions. A Golay cell detector is preceded by low-pass filters to suppress visible and near IR radiation, a band-pass filter, and a chopper. A prototype was assembled to demonstrate the new concept and the system performance. It can detect temperature variations smaller than 1 K for data sampled at a rate of 10/second, smoothed for intervals larger than 4 seconds. For a 76 ...

Resonance diffraction in the periodic array of graphene microribbons is theoretically studied following a recent experiment [L. Ju , Nature Nanotech.1748-338710.1038/nnano.2011.146 6, 630 (2011)]. Systematic studies over a wide range of parameters are presented. It is shown that a much richer resonant picture would be observable for higher relaxation times of charge carriers: More resonances appear and transmission can be totally suppressed. The comparison with the absorption cross-section of a single ribbon shows that the resonant features of the periodic array are associated with leaky plasmonic modes. The longest-wavelength resonance provides the highest visibility of the transmission dip and has the strongest spectral shift and broadening with respect to the single-ribbon resonance, due to collective effects.

Infrared emission from the dust shell around IRC+10216 is analyzed in detail, employing a self-consistent model for radiatively driven winds around AGB stars that couples the equations of motion and radiative transfer in the dust. The resulting model provides agreement with the wealth of available data, including the spectral energy distribution in the range 0.5-1000 microns, and visibility and array observations. Previous conclusions about two dust shells, derived from modeling the data with a few single-temperature components of different radii, are not supported by our results. The extended, continuous temperature and density distributions derived from our model obviate the need for such discrete shells. The IR properties vary with the stellar phase, reflecting changes in both the dust condensation radius r1 and overall optical depth tau - as the luminosity increases from minimum to maximum, r1 increases while tau decreases. We find that the angular size of the dust condensation zone varies from 0.3 arcsec...

Based on analytical scattering theory, we develop a multipolar expansion method to investigate systematically the near-field enhancement, far-field scattering and Local Density of States (LDOS) spectra in concentric metal-insulator-metal (MIM) cylindrical nanostructures, or coaxial plasmonic nanowires (CPNs). We demonstrate that these structures support distinctive plasmonic resonances with strongly reduced scattering in the far-field zone and significant electric field enhancement in deep sub-wavelength dielectric regions. Additionally, we study systematically the effects of geometrical parameters and dielectric index on the near-field and far-field plasmonic response of CPNs in the visible and near infrared spectral range. Finally, we demonstrate that CPNs provide a convenient approach for engineering strong (almost three orders of magnitude) LDOS enhancement in sub-wavelength dielectric gaps at multiple frequencies. These results enable the engineering of multiband optical detectors and CPNs-based light emitters with simultaneously enhanced excitation and emission rates for nanoplasmonics. PMID:20720997

As a key instrument for NASA s Earth Observing System (EOS), the Moderate Resolution Imaging Spectroradiometer (MODIS) has made significant contributions to the remote sensing community with its unprecedented amount of data products continuously generated from its observations and freely distributed to users worldwide. MODIS observations, covering spectral regions from visible (VIS) to long-wave infrared (LWIR), have enabled a broad range of research activities and applications for studies of the earth s interactive system of land, oceans, and atmosphere. In addition to extensive pre-launch measurements, developed to characterize sensor performance, MODIS carries a set of on-board calibrators (OBC) that can be used to track on-orbit changes of various sensor characteristics. Most importantly, dedicated and continuous calibration efforts have been made to maintain sensor data quality. This paper provides an overview of the MODIS calibration program, on-orbit calibration activities, methods, and performance. Key calibration results and lessons learned from the MODIS calibration effort are also presented in this paper.

During Rosetta’s flyby of the asteroid (2867) Šteins in 2008, we used the ALICE instrument to measure the first far-ultraviolet (FUV) reflectivity spectrum of an asteroid (850–2000Å). It is very dark in the FUV, ?4%, compared to its very high reflectivity (40%) at optical wavelengths. The FUV albedo does not exhibit a systematic color trend across the spectral range, but there is a broad absorption feature, not yet identified with a specific mineral, with maximum depth near 1650Å. The shape of this feature implies a very low abundance of Fe2+ ions in the surface minerals. The FUV brightness exhibits a significant opposition surge at phases below 10°. The visible/FUV color gets much redder with increasing phase angle inside the...

Observations of variable linear polarization in the optical range in the unique radio and X-ray source SS 433, which is characterized by moving emission lines in its visible and near-IR spectra, are reported. The observations were made with an unfiltered GaAs photocathode covering the spectral region 3000-9000 A, with a passband characteristic wavelength near 7000 A. Measurements reveal the presence of both a long-term and a very short time-scale variation in linear polarization in the continuum and in H-alpha, which indicate that a substantial fraction of the polarization is intrinsic to SS 433 and not produced in the interstellar medium. It is suggested that the most likely source of polarization in the optical continuum is electron scattering, and constraints on models of SS 433 implied by the discovery of intrinsic polarization are considered.

The only prominent line of singly ionized helium in the visible spectral range, He?ii?4686??, is observed together with the He?i?5015?? singlet and the He?i?4471?? triplet line in solar prominences. The Na D2 emission is used as a tracer for He?ii emissions which are sufficiently bright to exceed the noise level near 10?6 of the disk-center intensity. The prominences thus selected are characterized by small non-thermal line broadening and almost absent velocity shifts, yielding narrow line profiles without wiggles. The reduced widths [?? D/?] of He?ii?4686?? are 1.5 times broader than those of the He?i?4471?? triplet and 1.65 times broader than those of the He?i?5015?? singlet. This indicates that the He lines originate in a prominence?corona transition region with outwards increasing temp...

AMBER is the near-IR instrument for the VLTI, which will offer the possibility of combining two or three beams from either the 8 meter VLT main telescopes or the 1.8 meter auxiliary telescopes. With spectral dispersion up to 10,000 high visibility accuracy and the ability to obtain closure phases, AMBER will offer the means to perform high quality interferometric measurements in the 1 - 2.5 micron range initially, with later extensions to other portions of the spectrum. These design characteristics, coupled to the VLT interferometer potential, open up the access to investigation of several classes of objects, from stellar to extragalactic astronomy. We will review the projected performance in terms of sensitivity and angular resolution, and illustrate the potential applications in some key research areas. In particular, we will present the work of the AMBER Science Group, which is evaluating simulated data of source models and interferometric outputs for the purpose of defining the criteria for observations.

Effect of biaxial tensile strains on optical function and band edge transitions of ultra thin epitaxial films was studied using as an example a 13 nm thick SrTiO3 films deposited on KTaO3 (100) single-crystal substrates. Optical functions in the 200?1200 nm spectral range were determined by spectroscopic ellipsometry technique. It was found that tensile strains result in a shift of the low energy band gap optical transitions to higher energies and decrease the refractive index in the visible region. Comparison of the optical spectra for strained SrTiO3 films and for homoepitaxial strain-free SrTiO3: Cr (0.01 at %) films deposited on SrTiO3 (100) single crystalline substrates showed that this ?blue? shift of the band gap could not be related to technological imperfections or to reduced thic...

Abstract Transparent monoliths of urea cross-linked tripodal siloxane-based hybrids, named tri-ureasils, were prepared by the sol-gel process, using a wide concentration range of hydrochloric acid catalyst (1.0--10-3 - [HCl] - 2.0 M). The gelation time of the monoliths was controlled by varying the amount of water (2.2 and 22.2 mmol) and HCl (between 4.0--10-5 and 8.0--10-2 mmol) incorporated. Their local structure was characterized by X-ray diffraction, 29Si and 13C nuclear magnetic resonance, mid-infrared and ultraviolet/visible absorption spectroscopy, and photoluminescence in steady-state and time resolved modes. The effect of [HCl] in the enhancement of the emission quantum yield was quantified. Although all the hybrids display emission at room temperature in the blue spectral region,...

Tetracationic porphyrin dyes TMPyP and ZnPyP were intercalated into hydrophobized layered silicate films of three smectites. The smectites represented the layered silicate specimens of high (Fluorohectorite, Corning; FHT), medium (Kunipia F montmorillonite; KF) and low layer charge (Laponite, Laporte; LAP). The molecular orientations of the dye cations were studied by means of linearly-polarized ultraviolet-visible (UV-VIS) spectroscopy. The spectral analysis and consequent calculations of tilting angles of the transition moments at the wavelengths of Soret band transitions were in the range of 25?-35?. The determined angles indicated molecular orientation of the dye cations being almost parallel to the surface of the silicates. Slightly higher values (above 35?), determined for a FHT film...

Long-baseline interferometry at infrared wavelengths allows the innermost regions around young stars to be observed. These observations directly probe the location of the dust and gas in the disks. The characteristic sizes of these regions found are larger than previously thought. These results have motivated in part a new class of models of the inner disk structure, but the precise understanding of the origin of these low visibilities is still in debate. Mid-infrared observations probe disk emission over a larger range of scales revealing mineralogy gradients in the disk. Recent spectrally resolved observations allow the dust and gas to be studied separately showing that the Brackett gamma emission can find its origin either in a wind or in a magnetosphere and that there is probably no correlation between the location of the Brackett gamma emission and accretion. In a certain number of cases, the very high spatial resolution reveals very close companions and can determine their masses. Overall, these results...

Abstract The aim of the present paper was to examine the irradiation effect of two doses of UVA rays (365 nm) on the rabbit cornea and lens. Corneas of anesthetized adult albino rabbits were irradiated with UVA rays for 5 days (daily dose 1.01 J cm-2 in one group of rabbits and daily dose 2.02 J cm-2 in the second group of animals). The third day after the last irradiation, the rabbits were killed, and their eyes were employed for spectrophotometrical, biochemical and immunohistochemical investigations. Normal eyes served as controls. Absorption spectra of the whole corneal centers were recorded over the UV-VIS (visible) spectral range. Levels of antioxidant and prooxidant enzymes, nitric oxide synthases and nitric oxide (indirectly measured as nitrate concentration) were investigated in t...

Common extensions of the Standard Model of particle physics predict the existence of a "hidden" sector that comprises particles with a vanishing or very weak coupling to particles of the Standard Model (visible sector). For very light (m < 10^-14 eV) hidden U(1) gauge bosons (hidden photons), broad-band radio spectra of compact radio sources could be modified due to weak kinetic mixing with radio photons. Here, search methods are developed and their sensitivity discussed, with specific emphasis on the effect of the coherence length of the signal, instrumental bandwidth, and spectral resolution. We conclude that radio observations in the frequency range of 0.03--1400 GHz probe kinetic mixing of ~10^-3 of hidden photons with masses down to ~10^-17 eV. Prospects for improving the sensitivity with future radio astronomical facilities as well as by stacking data from multiple objects are discussed.

The pore structure and light transmission of high-silica porous glasses in the visible spectral range have been investigated as a function of the heat treatment temperature and the composition of the initial two-phase alkali borosilicate glass. The character of light transmission in porous glasses has been analyzed in the framework of the concepts of structural features of their pore space and the processes occurring in the porous glass during heating. It has been demonstrated that an increase in the temperature of heat treatment of porous glasses with different compositions leads to an increase in the pore size and a decrease in their specific surface area (with a nearly constant total porosity), which is associated with the processes of overcondensation of pores due to the rearrangement ...

Plasmonics has conventionally been in the realm of metal-optics. However, conventional metals as plasmonic elements in the near-infrared (NIR) and visible spectral ranges suffer from problems such as large losses and incompatibility with semiconductor technology. Replacing metals with semiconductors can alleviate these problems if only semiconductors could exhibit negative real permittivity. Aluminum doped zinc oxide (AZO) is a low loss semiconductor that can show negative real permittivity in the NIR. A comparative assessment of AZO-based plasmonic devices such as superlens and hyperlens with their metal-based counterparts shows that AZO-based devices significantly outperform at a wavelength of 1.55 µm. This provides a strong stimulus in turning to semiconductor plasmonics at the telecommunication wavelengths. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).

We report the synthesis of solvent-stabilized lead-iodide nanoparticles, using a convenient route involving coordinating solvents. The resultant colloids show strong absorption features in the ultraviolet region of the optical spectrum, which are consistent with the formation of semiconducting nanocrystals of lead (II) iodide. An effective-mass approximation model of quantum-confined states is in good agreement with the observed transition energies, giving strong indications of the particle morphologies and dimensions. Intense photoluminescence is also observed, with some spectral tuning possible with ripening time, giving a range of emission photon energies approximately spanning from 2.5 to 3.0 eV. We measure photo-stable luminescence quantum efficiencies of around 20% in solution, increasing to up to 30% if the coordinating ligand is exchanged for a Lewis-base capping layer. This demonstrates the potential for the utilization of lead-iodide nanocrystals in visible optoelectronics applications.

With an infrared transparency extended to 10mm, low multiphonon relaxation rates and suitable rare earth solubility, sulphide glasses in the Ge-Ga-Sb-S system allow radiative emission from rare earth ions in the mid-IR range. The Er3+ ion, widely studied in glass fibres for optical amplification at 1.5mm, presents an interesting transition for mid-IR applications around 4.5mm (4I9/24I11/2). Thus, the aim of this work is to evaluate the Er3+-doped Ge20Ga5Sb10S65 glass as a potential fibre laser source operating in the 3-5mm mid-IR spectral region. For that purpose, absorption and emission spectra were recorded from visible to mid-IR and the radiative lifetimes of the involved excited levels (4I9/2, 4I11/2 and 4I13/2) were determined. Experimental results were compared with those obtained fr...

The Zn0.9Mg0.1O thin films were prepared on Si (100) substrates by the sol-gel method. The structural and the optical properties of Zn0.9Mg0.1O thin films, submitted to an annealing treatment in the 400-700 degreeC ranges, are studied by X-ray diffraction (XRD) and ultraviolet (UV)-visible spectroscopic ellipsometry (SE). The thickness, refractive index, and extinction coefficient of these films have been determined by analyzing the SE spectra using parameterized dispersion model. Moreover, we made a detailed comparison among various dispersion models and found that the Sellmeier model was superior to others in fitting the ellipsometric spectra in the transparent region. In the interband transition region, point-by-point fit was used. The spectral dependence of the refractive index and ext...

Soft x-ray magneto-optic Kerr rotation has been measured using a continuously tunable multilayer linear polarizer in the beam reflected form samples in applied magnetic fields. Like magnetic circular dichroism, Kerr rotation in the soft x-ray can be element - specific and much larger than in the visible spectral range when the photon energy is tuned near atomic core resonances. Thus sensitive element-specific hysteresis measurements are possible with this technique. Examples showing large Kerr rotation from an Fe film and element-specific hysteresis loops of the Fe and Cr in an Fe/Cr multilayer demonstrate these new capabilities. Some consequences of the strong anomalous dispersion near the FeL{sub 2,3} edges to the Kerr rotation are discussed.

Foliar nitrogen has been shown to be positively correlated with midsummer canopy albedo and canopy near infrared (NIR) reflectance over a broad range of plant functional types (e.g., forests, grasslands, and agricultural lands). To date, the mechanism(s) driving the nitrogen???albedo relationship have not been established, and it is unknown whether factors affecting nitrogen availability will also influence albedo. To address these questions, we examined variation in foliar nitrogen in relation to leaf spectral properties, leaf mass per unit area, and leaf water content for three deciduous species subjected to either nitrogen (Harvard Forest, MA, and Oak Ridge, TN) or CO2 fertilization (Oak Ridge, TN). At Oak Ridge, we also obtained canopy reflectance data from the airborne visible/infrare...

Here we describe the configuration and operation of a field-use digital imaging system (multi-band spectrum camera, MBSC) that captures images in two spectral bands in the visible and near infrared wavelength ranges, and automatically converts and stores data as reflectance factor (RF) images. The instrument consists of a weatherproof camera unit, a skylight sensor and a PC and hard disc for a control unit. The camera unit has two industrial use digital camera boards attached with interference band-pass filters and objective lenses. The skylight sensor has light detectors equipped with band-pass filters identical to those used in the camera unit. The system is designed to collect images in each band and convert data into RF using the skylight intensity at prescheduled times. The MBSC has potential to automatically monitor agronomic variables in fields up to several hundred square meters.   

Gallium metallic photonic crystals with 100% filling factor have been fabricated via infiltration of liquid gallium into opals of 300-nm silica spheres using a novel high pressure-high temperature technique. The electrical resistance of the Ga-opal crystals was measured at temperatures from 10 to 280 K. The data obtained show that Ga-opal crystals are metallic network with slightly smaller temperature coefficient of resistivity than that for bulk gallium. Optical reflectivity of bulk gallium, plain opal and several Ga-opal crystals were measured at photon energies from 0.3 to 6 eV. A pronounced photonic stop band in the visible spectral range was found in both the plain and Ga infiltrated opals. The reflectivity spectra also show increase in reflectivity below 0.6 eV; which we interpret as a significantly lower effective plasma frequency of the metallic mesh in the infiltrated opal compare to the plasma frequency in the pure metal.

Antimony-doped tin oxide (SnO2:Sb, ATO) films have been deposited on glass substrates using atmospheric pressure chemical vapor deposition (APCVD) method. The precursors are mixed with SnCl4, SbCl5, and O2 to prepare the films. This study used synchrotron grazing incidence X-ray diffraction (GIXRD) to investigate the film microstructure. Our results show that the precursors of chlorine ions were involved in the doping mechanism, causing the microstructure of films to change slightly. The film has an average transmittance between 85.8 and 82.1% within a visible spectral range from 400 to 800 nm. The minimal resistivity was 6.1× 10-4 ? cm after doping. The synchrotron GIXRD data show that the chlorine ions caused the lattice constant change. A possible mechanism was proposed to explain the enhancement in electrical property due to chlorine dopants.

Tantalum oxide thin films were prepared by using reactive dc magnetron sputtering in the mixed atmosphere of Ar and O2 with various flow ratios. The structure and O/Ta atom ratio of the thin films were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The optical and dielectric properties of the Ta2O5 thin films were investigated by using ultraviolet-visible spectra, spectral ellipsometry and dielectric spectra. The results reveal that the structure of the samples changes from the amorphous phase to the b-Ta2O5 phase after annealing at 900^oC. The XPS analysis showed that the atomic ratio of O and Ta atom is a stoichiometric ratio of 2.50 for the sample deposited at Ar:O2=4:1. The refractive index of the thin films is 2.11 within the wavelength range 300-1000nm. The...

Among insulating materials containing point defects, lithium fluoride (LiF) is a radiation-sensitive alkali halide well known in dosimetry and as active medium in light-emitting devices and lasers. Electronic point defects can be produced in LiF crystals and films by different kinds of radiation. Some of these electronic defects, known as colour centres, are optically active, with broad absorption and emission bands in the visible spectral range. Novel thin-film imaging detectors for extreme ultraviolet and soft X-rays, based on photoluminescence from aggregated colour centres in LiF, have been proposed and are currently under development, successfully extending their operation also in the hard X-ray region, up to 10keV. Among the main peculiarities of LiF-based detectors, there are intrin...

We report on the realization of AlInP rolled-up microtubes that can be used as high refractive index optical resonators operating in the visible spectral range down to a wavelength of at least 530 nm. Furthermore, colloidal CdSe/CdS/ZnS core-shell-shell nanocrystals were deposited close to the microtube wall by fluid filling of the microtube and subsequent evaporation of the solvent. The optical modes of the microtube resonator are excited via coupling of the nanocrystals to the evanescent fields of the modes. By embedding the nanocrystal emitters in a polymer film, an enhanced nanocrystal stability is obtained. The film is studied by the built-in refractometer of the microtube.

This paper considers novel optical schemes that are related to acousto-optic systems for the spectral analysis of images. The systems are characterized by a low level of transverse and longitudinal chromatic aberrations. Mathematical expressions that describe the magnitudes of the transverse aberration in various configurations of acousto-optic filters are derived. A decrease in longitudinal chromatic aberrations is examined in an optical scheme that is based on a single objective lens and an additional negative lens. A similar analysis is carried out for a confocal system that is formed of two objective lenses. The experimental investigations carried out in the visible range of the spectrum demonstrated a decrease in the longitudinal shifts of images by a factor of 2.5 and by as much as t...

The problem of face identication in the Mid-Wave InfraRed (MWIR) spectrum is studied in order to understand the performance of intra-spectral (MWIR to MWIR) and cross-spectral (visible to MWIR) matching. The contributions of this work are two-fold. First, a database of 50 subjects is assembled and used to illustrate the challenges associated with the problem. Second, a set of experiments is performed in order to demonstrate the possibility of MWIR intra-spectral and cross-spectral matching. Experiments show that images captured in the MWIR band can be eciently matched to MWIR images using existing techniques (originally not designed to address such a problem). These results are comparable to the baseline results, i.e., when comparing visible to visible face images. Experiments also show that cross-spectral matching (the heterogeneous problem, where gallery and probe sets have face images acquired in dierent spectral bands) is a very challenging problem. In order to perform cross-spectral matching, we use multiple texture descriptors and demonstrate that fusing these descriptors improves recognition performance. Experiments on a small database, suggests that the problem of cross-spectral matching requires further investigation.

This concept comprises a method for environmentally clean destruction of undesirable plant life using visible or infrared radiation. We believe that during the blossom stage, plant life is very sensitive to electromagnetic radiation, with an enhanced sensitivity to specific spectral ranges. Small doses of irradiation can arrest further plant growth, cause flower destruction or promote plant death. Surrounding plants, which are not in the blossoming stage, should not be affected. Our proposed mechanism to initiate this effect is radiation produced by a laser. Tender parts of the blossom possess enhanced absorptivity in some spectral ranges. This absorption can increase the local tissue temperature by several degrees, which is sufficient to induce bio-tissue damage. In some instances, the radiation may actually stimulate plant growth, as an alternative for use in increased crop production. This would be dependent on factors such as plant type, the wavelength of the laser radiation being used and the amount of the radiation dose. Practical, economically viable realization of this concept is possible today with the advent of high efficiency, compact and powerful laser diodes. The laser diodes provide an efficient, environmentally clean source of radiation at a variety of power levels and radiation wavelengths. Figure 1 shows the overall concept, with the laser diodes mounted on a movable platform, traversing and directing the laser radiation over a field of opium poppies.

Conventional CW (continuous-wave) spectroscopy is a process where the excitation sources pump the sample at constant intensity over the time required to perform the measurement. The end result is an emission or scattering spectrum. which in many cases is inadequate because limited discriminatory capability. The main problem for Raman effect is its weakness relatively to background luminescence. Gated Raman enables to overcome this because the Raman interaction time is virtually instantaneous, whereas luminescence is slower, with minimum hundreds of picoseconds decay time. Our detection system is gated so as to detect only photons scattered or emitted during the laser pulse. Thus we will collect all of the Raman photons but reject the majority of the luminescence. Consequently Raman and luminescence are separated in time domain. Gated UV Raman technique gives additional advantages. In the UV range with very energetic photons, the Raman lines are very close to excitation, while in this spectral range the luminescence is very weak because of Stocks shift. Thus Raman and luminescence are separated in spectral domain. Besides, UV Raman cross section is enhanced strongly because of (1/lambda)(exp 4) dependence and even much higher at the vicinity of allowed electronic transitions. In Laser Induced Breakdown Spectroscopy (LIBS), the plasma light created by laser is analyzed to determine the elemental composition of the sample. Combination of visible Raman and LIBS techniques has been proposed for remote detection of minerals for planetary applications.

Phase reddening is an effect that produces an increase of the spectral slope and variations in the strength of the absorption bands as the phase angle increases. In order to understand its effect on spectroscopic observations of asteroids, we have analyzed the visible and near-infrared spectra (0.45-2.5 ?m) of 12 near-Earth asteroids observed at different phase angles. All these asteroids are classified as either S-complex or Q-type asteroids. In addition, we have acquired laboratory spectra of three different types of ordinary chondrites at phase angles ranging from 13° to 120°. We have found that both, asteroid and meteorite spectra show an increase in band depths with increasing phase angle. In the case of the asteroids the Band I depth increases in the range of ˜2° 30°. Variations in band centers and band area ratio (BAR) values were also found, however they seems to have no significant impact on the mineralogical analysis. Our study showed that the increase in spectral slope caused by phase reddening is comparable to certain degree of space weathering. In particular, an increase in phase angle in the range of 30-120° will produce a reddening of the reflectance spectra equivalent to exposure times of ˜0.1 × 106-1.3 × 106 years at about 1 AU from the Sun. This increase in spectral slope due to phase reddening is also comparable to the effects caused by the addition of different fractions of SMFe. Furthermore, we found that under some circumstances phase reddening could lead to an ambiguous taxonomic classification of asteroids.

In wheat (Triticum aestivum L.) plants, deficiency of an essential element may drastically affect growth, appearance, and most importantly yield. Wheat, the focus of this study, is one of the crops studied in the CELSS program. Information about nutrient deficiencies in crops grown in controlled environment is essential to optimize food productivity. The main objective of this study was to determine whether deficiency of Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca) and Magnesium (M) alters spectral reflectance properties of wheat leaves. Plants were grown in the greenhouse and growth chamber, in a modified Hoagland’s nutrient solution. Spectral reflectance of fully expanded wheat leaves from 280 to 1100 nm, nutrient concentrations (N, P, K, and Ca) and chlorophyll (Chl) were determined when deficiency symptoms were first evident (?6 7 weeks). Chlorophyll content and fresh and dry weight, were used to assess the severity of the nutrient stress. All nutrient deficiencies affected chlorophyll content and generally increased reflectance in the visible (VIS) 400 700 nm and infrared (IR) 700 1100 nm ranges. Magnesium and nitrogen deficiencies had the most pronounced effect on chlorophyll concentration height, and reflectance. All macronutrient deficiencies tested reduced chlorophyll concentration, increase reflectance in the visible range and caused a shift in the position of the red edge (the point of maximum slope on the reflectance spectrum of vegetation between red and near-infrared wavelengths) toward shorter or longer wavelengths; depending upon the element. In the greenhouse, N and Mg induced the greatest increase in reflectance of 33% and 25% in the VI range and 86% and 53% in the IR range, respectively. However, in the growth chamber, an increase of 97% and 25% occurred in the VI range, and 20% and 33% in the IR range, respectively. In the IR range in the growth chamber, P, K, and Ca deficiency caused a reduction in reflectance (412 770 nm). This research indicates that mineral deficiencies and reflectance are not specific to one environment and could have important implications for the design of CELSS in space, and perhaps the future of terrestrial agriculture.

Context. Spectropolarimetry at high spatial and spectral resolution is a basic tool to characterize the magnetic properties of the solar atmosphere. Aims: We introduce the KIS/IAA Visible Imaging Polarimeter (VIP), a new post-focus instrument that upgrades the TESOS spectrometer at the German Vacuum Tower Telescope (VTT) into a full vector polarimeter. VIP is a collaboration between the Kiepenheuer Institut für Sonnenphysik (KIS) and the Instituto de Astrofísica de Andalucía (IAA-CSIC). Methods: We describe the optical setup of VIP, the data acquisition procedure, and the calibration of the spectropolarimetric measurements. We show examples of data taken between 2005 and 2008 to illustrate the potential of the instrument. Results: VIP is capable of measuring the four Stokes profiles of spectral lines in the range from 420 to 700 nm with a spatial resolution better than 0farcs5. Lines can be sampled at 40 wavelength positions in 60 s, achieving a noise level of about 2 × 10-3 with exposure times of 300 ms and pixel sizes of 0farcs17 × 0farcs17 (2 × 2 binning). The polarization modulation is stable over periods of a few days, ensuring high polarimetric accuracy. The excellent spectral resolution of TESOS allows the use of sophisticated data analysis techniques such as Stokes inversions. One of the first scientific results of VIP presented here is that the ribbon-like magnetic structures of the network are associated with a distinct pattern of net circular polarization away from disk center. Conclusions: VIP performs spectropolarimetric measurements of solar magnetic fields at a spatial resolution that is only slightly worse than that of the Hinode spectropolarimeter, while providing a 2D field field of view and the possibility to observe up to four spectral regions sequentially with high cadence. VIP can be used as a stand-alone instrument or in combination with other spectropolarimeters and imaging systems of the VTT for extended wavelength coverage.

Abstract The use of visible light in photocatalysis has been intensively studied because of its natural abundance, ease of use, and promising potential for industrial applications. However, there are several challenges to utilizing visible light for organic functional group transformations. These challenges include the low absorptivity of most organic compounds in the visible spectrum, and side reactions are often prevalent in photochemical reactions. Visible-light-sensitive catalysts offer a means to overcome these obstacles. Conjugated polymers are semiconductors that offer a large range of redox potentials, they are stable, and they often absorb visible light. Despite these desirable properties for photocatalysis, only a limited number of organic reactions utilizing conjugated polymers ...

We describe a method for the preparation of a polyurethane phantom to simulate the optical properties of biologic tissues at two wavelengths in the visible and near-infrared spectral range. We characterize the addition of added molecular absorbers with relatively narrow absorption bands [full width at half maximum (FWHM) 32 and 76 nm for Epolight 6084 and 4148, respectively] for independent absorption at 690 nm for absorption up to 5 cm-1, and 830 nm for absorptions up to 3 cm-1. Absorption by both dyes is linear with concentration in these respective regions and is consistent in polyurethane both before and after curing. The dyes are stable over long durations with no more than 4% change. The absorption of visible light by polyurethane decreases with time and is stable by one year with a drop of 0.03+/-0.003 cm-1 from 500 to 830 nm. The scattering properties are selected by the addition of TiO2 particles to the polyurethane, which we functionally describe for the 690- and 830-nm wavelengths as related to the weight per volume. We demonstrate that the variation in absorption and scattering properties for large batch fabrication (12 samples) is +/-3%. The optical properties of the phantoms have not significantly changed in a period of exceeding one year, which makes them suitable for use as a reference standard.

On July 4 2005 the NASA spacecraft Deep Impact delivered an impactor on the comet 9P Tempel 1 to study the material underneath the surface of the nucleus A worldwide observation campaign accompanied the mission to characterize the activity of Tempel 1 before and after the impact At La Palma Canary Islands the comet was observed from July 2 to July 9 using the echelle spectrograph SARG on the Telescopio Nazionale Galileo TNG The spectra have been obtained using a slit 8 arcsec long providing a resolving power R 29000 in the spectral range 4620-7920 A Most of the lines found in the spectra can be attributed to C2 NH2 and CN the atomic oxygen lines both the green line at 5577 A and the red doublet at 6300 and 6364 A are clearly visible in every spectrum All these emission lines have been catalogued and identified using as a comparison list the catalogue obtained from a spectrum of 153P 2002 Ikeya-Zhang taken on April 20 2002 1 2 One of our aims is also to compare between them these spectra looking for differences in the lines visible in the orders before and after the impact References 1 Cremonese G et al 2006 A A in press 2 Capria M T et al 2005 A A 442 1121-1126

The Odin satellite, which carries two instruments, OSIRIS and SMR, was launched to a heliosyncronous orbit in February 2001. The observation time is divided between aeronomical and astronomical measurements. In aeronomy mode OSIRIS and SMR will scan the limb either in a continuous or in a stepwise manner from tangent altitudes of 60 (alternatively 120 km) to 7 km. OSIRIS includes an UV-visible spectrometer and an infrared imager. SMR is a sub-millimeter radiometer, which is used for both aeronomy and astronomy measurements. In this paper we present a Modified Onion Peeling (MOP) method to retrieve minor species densities from limb scatter measurements by OSIRIS. The goal is to retrieve vertical profiles of ozone, NO2, OClO and BrO density, and also aerosol and Rayleigh extinction. The need for absolute calibration of the radiance measurement is circumvented by dividing the data with a reference measurement made at a high tangent altitude by the same instrument. We approximate the atmosphere to be, at least in the first order, locally spherically symmetric. This leads to a non-linear inversion problem. Multiple scattering is taken into account by pre-calculated total to single scattering radiance ratios tabulated as a function of wavelength, tangent altitude, and several other relevant parameters. The inversion uses the whole UV-visible spectral range of OSIRIS. Several constituents are inverted simultaneously. We show preliminary retrieval results from selected OSIRIS measurements. Odin is a Swedish-led satellite project funded jointly by Sweden (SNSB), Canada (CSA), Finland (Tekes) and France (CNES).

The Optical Assembly (OA) for the Multispectral Thermal Imager (MTI) program has been fabricated, assembled, and successfully tested for its performance. It represents a major milestone achieved towards completion of this earth observing E-O imaging sensor that is to be operated in low earth orbit. Along with its wide-field-of-view (WFOV), 1.82{degree} along-track and 1.38{degree} cross-track, and comprehensive on-board calibration system, the pushbroom imaging sensor employs a single mechanically cooled focal plane with 15 spectral bands covering a wavelength range from 0.45 to 10.7 {micro}m. The OA has an off-axis three-mirror anastigmatic (TMA) telescope with a 36-cm unobscured clear aperture. The two key performance criteria, 80% enpixeled energy in the visible and radiometric stability of 1% 1{sigma} in the visible/near-infrared (VNIR) and short wavelength infrared (SWIR), of 1.45% 1{sigma} in the medium wavelength infrared (MWIR), and of 0.53% 1{sigma} long wavelength infrared (LWIR), as well as its low weight (less than 49 kg) and volume constraint (89 cm x 44 cm x 127 cm) drive the overall design configuration of the OA and fabrication requirements.

In this paper we study the tailoring of photon spectral properties generated by four-wave mixing in a birefringent photonic crystal fibre (PCF). The aim is to produce intrinsically narrow-band photons and hence to achieve high non-classical interference visibility and generate high fidelity entanglement without any requirement for spectral filtering, leading to high effective detection efficiencies. We show unfiltered Hong-Ou-Mandel interference visibilities of 77% between photons from the same PCF, and 80% between separate sources. We compare results from modelling the PCF to these experiments and analyse photon purities.

Both plants and animals have one general commonality in their perception of light. They both are sensitive primarily to the 400 to 700 nm wavelength portion of the electromagnetic spectrum. This is referred to as the visible spectrum for animals and as the photosynthetically active radiation (PAR) spectrum for plants. Within this portion of the spectrum, animals perceive colors. Relatively recently it has been learned that within this same spectral range plants also demonstrate varying responses at different wavelengths, somewhat analogous to the definition of various colors at specific wavelengths. Although invisible to the human eye, portions of the electromagnetic spectrum on either side of the visible range are relatively inactive photosynthetically but have been found to influence important biological functions. These portions include the ultraviolet (UV approximately equal to 280-400 nm) and the far-red (FR approximately equal to 700-800 nm). The basic photoreceptor of plants for photosynthesis is chlorophyll. It serves to capture radiant energy which combined with carbon dioxide and water produces oxygen and assimulated carbon, used for the synthesis of cell wall polysaccarides, proteins, membrane lipids and other cellular constituents. The energy and carbon building blocks of photosynthesis sustain growth of plants. On the other hand, however, there are other photoreceptors, or pigments, that function as signal transducers to provide information that controls many physiological and morphological responses of how a plant grows. Known photomorphogenic receptors include phytochrome (the red/far-red sensor in the narrow bands of 655-665 nm and 725-735 nm ranges, respectively) and 'cryptochrome' (the hypothetical UV-B sensor in the 280-320 nm range). Since the USDA team of W. L. Butler, S. B. Hendricks, H. A. Borthwick, H. A. Siegleman and K. Norris in Beltsville, MD detected by spectroscopy, extracted and identified phytochrome as a protein in the 1950's, many other investigators have found evidence of its control functions in plants. Considerably less, however, is known about the yet non-isolated cryptochrome. The information-transferring roles of photoreceptors in plants at specific spectral ranges quite naturally stimulated plant scientists and engineers to consider physically manipulating light to achieve desired physiological and morphological characteristics. One way to manipulate light is to filter it through materials that selectively transmit portions of the sun's spectrum in and near the PAR range.

The relaxation dynamics of electronically excited [Au25(SR)18]q, where q = 0 or -1 and SR = S(CH2)2Ph, were studied using femtosecond time-resolved transient absorption spectroscopy. Nanoclusters excited by 400 nm light were probed using temporally delayed broad-bandwidth continuum probe pulses. Continuum pulses were generated in both the visible and near infrared (NIR) spectral regions, providing access to a wide range of transient spectral features. The use of NIR probe pulses allowed the relaxation dynamics of the excited states located near the HOMO-LUMO energy gap to be monitored in the probe step via the sp absorption (ESA) data that were much less congested than the typical visible transient spectrum. For the neutral nanocluster, the time-domain data were composed of three components: (1) a few-picosecond decay, (2) a slower decay taking a few hundred picoseconds and (3) a non-decaying plateau function. Component 1 reflected energy relaxation to semi-ring ligand states; component 2 was attributed to relaxation via a manifold of states located near the HOMO-LUMO energy gap. Component 3 arose from slow radiative recombination. The dynamics of the anion depended upon the identity of the excited state from which the particle was relaxing. The LUMO+1 state of the anion exhibited relaxation dynamics that were similar to those observed for the neutral nanocluster. By comparison, the time-domain data observed for the LUMO state contained only two components: (1) a 3.3 +/- 0.2 ps decay and (2) a 5 +/- 1 ns decay. The amplitude coefficients of each component were also analyzed. Taken together, the amplitude coefficients and lifetimes were indicative of an activation barrier located approximately 100 meV above the HOMO-LUMO energy gap, which mediated a previously unobserved excited state decay process for [Au25(SR)18]0. These data suggested that NIR ESA measurements will be instrumental in describing the relaxation processes of quantum-confined nanoclusters.

The short-wave transmission spectrum of Na0.4Lu0.6F2.2 with the visible/ultraviolet transmission edge of 8 eV was studied. Absorption spectra of the 4f?5d transitions of the Ce3+ ion in the region of 4?8 eV were studied in Ce3+-doped Na0.4Lu0.6F2.2 single crystals. Luminescence spectra in the ultraviolet and visible spectral regions, luminescence decay kinetics and reflection and luminescence excitation spectra in the visible/ultraviolet and ultraviolet regions (4?20 eV) were investigated at helium and room temperatures.

The Ontar Corporation (www.Ontar.com) has developed several products for atmospheric remote sensing to calculate radiative transport, atmospheric transmission, and sensor performance in both the normal atmosphere and the atmosphere disturbed by battlefield conditions of smoke, dust, explosives and turbulence. These products include: PcModWin: Uses the USAF standard MODTRAN model to compute the atmospheric transmission and radiance at medium spectral resolution (2 cm-1) from the ultraviolet/visible into the infrared and microwave regions of the spectrum. It can be used for any geometry and atmospheric conditions such as aerosols, clouds and rain. PcLnWin: Uses the USAF standard FASCOD model to compute atmospheric transmission and emission at high (line-by-line) spectral resolution using the HITRAN 2000 database. It can be used over the same spectrum from the UV/visible into the infrared and microwave regions of the spectrum. HitranPC: Computes the absolute high (line-by-line) spectral resolution transmission spectrum of the atmosphere for different temperatures and pressures. HitranPC is a user-friendly program developed by the University of South Florida (USF) and uses the international standard molecular spectroscopic database, HITRAN. LidarPC: A computer program to calculate the Laser Radar/L&n Equation for hard targets and atmospheric backscatter using manual input atmospheric parameters or HitranPC and BETASPEC - transmission and backscatter calculations of the atmosphere. Also developed by the University of South Florida (USF). PcEosael: is a library of programs that mathematically describe aspects of electromagnetic propagation in battlefield environments. 25 modules are connected but can be exercised individually. Covers eight general categories of atmospheric effects, including gases, aerosols and laser propagation. Based on codes developed by the Army Research Lab. NVTherm: NVTherm models parallel scan, serial scan, and staring thermal imagers that operate in the mid and far infrared spectral bands (3 to 12 micrometers wavelength). It predicts the Minimum Resolvable Temperature Difference (MRTD) or just MRT) that can be discriminated by a human when using a thermal imager. NVTherm also predicts the target acquisition range performance likely to be achieved using the sensor.

EChO, a space mission for exoplanets exploration, is considered the next step for planetary atmospheres characterization. It will be a dedicated observatory to uncover a large selected sample of planets spanning a wide range of masses (from gas giants to super-Earths) and orbital temperatures (from hot to habitable). All targets move around stars of spectral types F, G, K, and M. EChO will provide an unprecedented view of the atmospheres of planets in the solar neighbourhood. The consortium formed by various institutions of different countries is proposing an integrated spectrometer payload for EChO covering the wavelength interval 0.4 to 16 µm. This instrument is subdivided into 4 channels: a visible channel, which includes a fine guidance system (FGS) and a VIS spectrometer, a near infrared channel (SWiR), a middle infrared channel (MWiR), and a long wave infrared module (LWiR). In addition, it contains a common set of optics spectrally dividing the wavelength coverage and injecting the combined light of parent stars and their exoplanets into the different channels. The proposed payload meets all of the key performance requirements detailed in the ESA call for proposals as well as all scientific goals. EChO payload will be based on different spectrometers covering the spectral range mentioned above. Among them, SWiR spectrometer will work from 2.45 microns to 5.45 microns. In this paper, the optical and mechanical designs of the SWiR channel instrument, including the evolution of the different trades followed and the current identification of critical points, are reported on.

The main goal of this project is to develop a generic approach to synthesise any wavelength in the visible and UV spectral region based on sum frequency generation. The approach is based on a hybrid system combining solid state and semiconductor technology. The generation of light in the UV spectral region require nonlinear materials with a transparency range extending into the ultraviolet, the ability to sustain high photon energies and with the ability to obtain phasematching for the desired nonlinear conversion process. In this project experiments are conducted using three differently co-doped GdCOB crystals. The crystals are optimized for noncritical phasematching in the blue-UV spectral region through co-doping with Lu and Sc, a nonlinear coefficient for these crystals of 0.78, 0.81 and 0.89 pm/V are measured, which is comparable to LBO. The ability to adjust the noncritical phasematching by co-doping of these crystals makes them promising candidates for generation of light in the blue-UV region. A novelmethod for cavity dumping based on nonlinear frequency conversion is investigated. A high finesse laser is constructed with an intracavity nonlinear material inserted in a beam waist. The nonlinear material is phasematched to support sum frequency generation between the 1342nm circulating field in the cavity and a single pass passively Q-Switched 1064nm laser, effectively converting the circulating power whenever a single pass pulse is present. Furthermore the Q-Switched laser can easily be frequency doubled in a single pass configuration, therefore the nonlinear cavity dumping approach is suggested for the generation of 340nm UV light, using 532nm pulses to cavity dump a 946nm Nd:YAG laser. Furthermore experiments are conducted tripling a Q-switched 1064nm laser to 355nm by cascaded second harmonic and sum frequency generation using periodically poled KTP and BBO for the SHG and SFG process, respectively. The 355nm light is used to promote different photo induced reactions. The main limitation of reaching any desired wavelength in the visible spectrum using sum frequency generation is the limited laser lines available from efficient solid state lasers. One fundamental way to overcome this limitation is to use semiconductor lasers to provide one of the fundamental fields. The problem of using semiconductor lasers for nonlinear frequency conversion has previously been the lag of coherence of these devices. This problem can, however, to a large extent be solved using external cavity tapered diode lasers, which allows for the generation of coherent radiation at the watt power level. Using differently doped semiconductor materials these devices can potentially cover the wavelength range from the red and into the infrared spectral range. These devices are very efficient, however, the available devices in the visible region are still very inefficient, therefore a generic approach using high finesse solid state lasers with intracavity nonlinear materials and single pass tapered diode was sought to cover the shorter wavelength range. In this project more then 300mW of 488nm power is generated by direct sum frequency mixing of a solid state laser and a single pass external cavity tapered diode laser. The performance of the device is compared to systems where the output of the tapered diode laser is spatially filtered and to an all solid state laser system based on mixing with a single frequency Ti:Sapphire laser. Finally experiments with a semiconductor disk laser used as the high finesse cavity laser and sum frequency mixing with a single pass solid state laser is coniv ducted. These experiments show that it is possible to design systems exploiting the benefits of semiconductor based lasers and nonlinear sum frequency generation to cover large parts of the optical spectrum, which has previously been difficult to access due to the lag of efficient, coherent light sources

Animal coloration functions for display or camouflage. Notably insects provide numerous examples of a rich variety of the applied optical mechanisms. For instance, many butterflies feature a distinct dichromatism, that is, the wing coloration of the male and the female differ substantially. The male Brimstone, Gonepteryx rhamni, has yellow wings that are strongly UV iridescent, but the female has white wings with low reflectance in the UV and a high reflectance in the visible wavelength range. In the Small White cabbage butterfly, Pieris rapae crucivora, the wing reflectance of the male is low in the UV and high at visible wavelengths, whereas the wing reflectance of the female is higher in the UV and lower in the visible. Pierid butterflies apply nanosized, strongly scattering beads to achieve their bright coloration. The male Pipevine Swallowtail butterfly, Battus philenor, has dorsal wings with scales functioning as thin film gratings that exhibit polarized iridescence; the dorsal wings of the female are matte black. The polarized iridescence probably functions in intraspecific, sexual signaling, as has been demonstrated in Heliconius butterflies. An example of camouflage is the Green Hairstreak butterfly, Callophrys rubi, where photonic crystal domains exist in the ventral wing scales, resulting in a matte green color that well matches the color of plant leaves. The spectral reflection and polarization characteristics of biological tissues can be rapidly and with unprecedented detail assessed with a novel imaging scatterometer-spectrophotometer, built around an elliptical mirror [1]. Examples of butterfly and damselfly wings, bird feathers, and beetle cuticle will be presented. [4pt] [1] D.G. Stavenga, H.L. Leertouwer, P. Pirih, M.F. Wehling, Optics Express 17, 193-202 (2009)

A study has been made of the fluorescence of poly d(G-m5C).poly d(G-m5C), a synthetic double-stranded DNA, in buffered neutral aqueous solution at room temperature, excited by synchrotron radiation at 280 nm and 250 nm and by a frequency-doubled pulse dye laser at 290 nm. Exciting at 280 nm, the B form shows a uni-modal UV spectrum with lambdaf(max) approximately 340 nm. The Z form has in addition a visible emission lambdaf(max) at 450 nm. The spectral positions remain unchanged on exciting at 250 nm but the relative intensities change considerably. Decay profiles have been obtained at 360 nm and 450 nm for both the B and Z forms and have been analyzed by fitting to a pseudo-continuous distribution of 100 (and occasionally 200) exponentials, ranging from 10 ps to 20 ns, by optimizing the 'entropy' of the signal (the method of maximum entropy). We find the mean lifetimes for both wavelengths of emission and for both structural forms fall into three well-separated regions in the ranges indicated tau1 approximately 0.04-0.21 ns, tau2 approximately 0.9-1.26 ns, and tau3 approximately 5.1-6.5 ns. The UV emission, from its spectral position and half-width, correlates with monomeric emission from m5C (and from C for poly d(G-C)). However the lifetime tau1 is approximately 2 orders of magnitude longer than the monomers and points to an involvement of protonated guanosine (GH+, tauf approximately 200 ps) in the overall absorption/emission sequence. In the UV the tau3 emission is predominant, with fractional time-integrated emission approximately 86% for B DNA and approximately 64% for Z. We suggest it results from exciton (stacked) absorption followed by dissociative emission. For Z DNA the visible (450 nm) emission is dominated by a tau3 species (approximately 91%) with a lifetime of 6.5 ns and we suggest it represents a hetero-excimer emission consequent upon absorption by the strongly overlapped base-stacking, which differs from that in B DNA. The weak emission corresponding to tau2 is made more apparent by scanned gated detection of the emission from laser excitation (290 nm) of single-crystal d(m5C-G)3. A central role is attributed to the tight stacking of the bases in the Z form which correlates with enhanced hypochromism at 250 nm vs. 280 nm and with the reversal of the fluorescence intensity ratios UV-visible between these wavelengths. PMID:17668119

We evaluated the accuracy, sensitivity and precision of a multiple pathlength, liquid core waveguide (MPLCW) system for measuring colored dissolved organic matter (CDOM) absorption in the UV-visible spectral range (370-700 nm). The MPLCW has four optical paths (2.0, 9.8, 49.3, and 204 cm) coupled to a single Teflon AF sample cell. Water samples were obtained from inland, coastal and ocean waters ranging in salinity from 0 to 36 PSU. Reference solutions for the MPLCW were made having a refractive index of the sample. CDOM absorption coefficients, aCDOM, and the slope of the log-linearized absorption spectra, S, were compared with values obtained using a dual-beam spectrophotometer. Absorption of phenol red secondary standards measured by the MPLCW at 558 nm were highly correlated with spectrophotometer values and showed a linear response across all four pathlengths. Values of aCDOM measured using the MPLCW were virtually identical to spectrophotometer values over a wide range of concentrations. The dynamic range of aCDOM for MPLCW measurements was 0.002 - 231.5 m-1. At low CDOM concentrations spectrophotometric aCDOM were slightly greater than MPLCW values and showed larger fluctuations at longer wavelengths due to limitations in instrument precision. In contrast, MPLCW spectra followed an exponential to 600 nm for all samples.