Near-infrared Wavelength Region Research Articles

Highly damage resistant, broadband, hard antireflection coating for high power lasers in the ultraviolet to near-infrared wavelength regions

Mechanically hard and broadband gradient refractive index antireflection coating was developed. It has a high damage threshold of ≳6 J/cm2 at 355 nm and 12–13 J/cm2 in the visible to near-infrared region. It will be applicable to high power pulsed lasers as well as to industrial uses.

Periscope-camera system for visible and infrared imaging diagnostics on TFTR

An optical diagnostic consisting of a periscope which relays images of the torus interior to an array of cameras is used on the Tokamak Fusion Test Reactor (TFTR) to view plasma discharge phenomena and inspect the vacuum vessel internal structures in both the visible and near-infrared wavelength regions. Three periscopes view through 20-cm-diam fused-silica windows which are spaced around the torus midplane to provide a viewing coverage of approximately 75% of the vacuum vessel internal surface area. The periscopes have f/8 optics and motor-driven controls for focusing, magnification selection (5°, 20°, and 60° field of view), elevation and azimuth setting, mast rotation, filter selection, iris aperture, and viewing port selection. The four viewing ports on each periscope are equipped with multiple imaging devices which include: (1) an inspection eyepiece, (2) standard (RCA TC2900) and fast (RETICON) framing rate television cameras, (3) a PtSi CCD infrared imaging camera, (4) a 35-mm Nikon F3 still camera, or (5) a 16-mm Locam II movie camera with variable framing rate up to 500 fps. Operation of the periscope-camera system is controlled either locally or remotely through a computer-CAMAC interface. A description of the equipment and examples of its application are presented.

LANDSAT Thematic Mapper bands for characterizing fescue grass vegetation

Abstract The relationships between reflectance in the LANDSAT Thematic Mapper (TM) bands and grass canopy characteristics were studied. Data were collected from a total of 107 tall fescue (Festuca arundinacia) plots (0·2 m2) during the 1983 growing season. Canopy height, percentage cover, total wet biomass, total dry biomass, plant water and leaf area index were correlated with spectral data obtained from a Barnes Modular Multiband Radiometer. The near-infrared wavelength region corresponding to TM band 4 appeared to be the best estimator of total wet biomass (r = 0·80) and canopy height (r =0·82). Percentage canopy cover had the highest correlation coefficients with TM band 7 (r = −0·95) and TM bands 1, 2 and 3 (r≥0·93). All canopy variables showed a curvilinear relationship with the spectral bands, except canopy cover, which showed a near linear relationship, for the biomass range in this study. Linear transformations were obtained using natural logarithms of the grass canopy variables and the spectral ...

A highly sensitive chalcogenide photoconductor in a near-infrared wavelength region

A new highly sensitive photoconductor in a near-infrared wavelength region with a low dark decay has been developed for an electrophotographic device. The photoconductor has been created with a multilayered Se-As-Te chalcogenide glass. The structure of the photoconductive layer consists of four parts: (a) Se-rich blocking layer, (b) Te-rich IR-sensitive layer, (c) As-rich space-charge layer, and (d) Se-rich voltage sustaining layer. A Cerium oxide layer is interposed as a carrier blocking layer on the substrate. This photoconductor has shown sensitivity of about 300 m2/J to beams having a wavelength of 750 nm. This sensitivity is as high as that of the amorphous Se photoconductor to light having a wavelength of 442 nm. This photoconductor has favorable characteristics such as a high initial surface potential, low dark decay, low residual surface potential, and long durability in practical use. It is suitable for a photoconductor in a laser beam printer with a diode laser.

A Method for Determining the Single Scattering Albedo of Clouds Through Observation of the Internal Scattered Radiation Field

A method is presented for determining the single scattering albedo of clouds at selected wavelengths in the visible and near-infrared wavelength regions. The procedure compares measurements of the ratio of the zenith to nadir propagating intensities deep within a cloud layer with radiative transfer computations of the same. Analytic formulas are derived which explicitly show the dependence of the internal intensity ratio on ground albedo, optical depth, single scattering albedo and cloud asymmetry factor. The single scattering albedo and cloud asymmetry factor enter the solution in such a way that a similarity relationship exists between these two parameters. As a result, the accuracy with which the single scattering albedo can be determined is dictated by the accuracy with which the asymmetry factor can be estimated. A method of observation is described whereby aircraft measurements of the zenith and nadir propagating intensities can be used to determine the similarity parameter as a function of wavelength. Since the fractional absorption of a cloud depends on the similarity parameter and not on the single scattering albedo and asymmetry factor separately, this poses no severe limitation to the method. An accurate knowledge of the ground albedo and total optical thickness of a cloud are unnecessary for a solution, provided one associates the wavelength for which the intensity ratio is a maximum with conservative scattering. Under this internal calibration approach, uncertainties in the ground atbedo are very nearly compensated by uncertainties in the cloud optical thickness.

Spectral Variation of Optical Depth at Tucson, Arizona between August 1975 and December 1977

A multi-wavelength solar radiometer has been used to monitor the directly transmitted solar radiation at discrete wavelengths spaced through the visible and near-infrared wavelength regions. The relative irradiance of the directly transmitted sunlight at each wavelength was measured during the course of each cloud-free day, from which the total optical depth of the atmosphere was determined using the BouguerLangley method. From the spectral variation of total optical depth the ozone absorption optical depths, and hence total ozone content of the atmosphere, have been derived. By subtracting the molecular scattering and estimated ozone absorption contributions from the total optical depth, the aerosol optical depth for each day and wavelength can be determined provided the wavelengths selected have no additional molecular absorption bands. Results of this analysis for 133 clear stable days at Tucson, Arizona are presented for a 29month period between August 1975 and December 1977. Monthly averages of the total and aerosol optical depths are presented for five wavelengths between 0.4400 and 0.8717 pm. The aerosol optical depth obtains a maximum in July and August with a secondary maximum in April and May. The median aerosol optical depth for the entire data set decreases with wavelength from 0.0508 (A = 0.4400 pm) to 0.0306 (A = 0.8717 pm). Also presented are daily values of total ozone content which exhibit the characteristic seasonal cycle with peak values in early May and an annual mean value of 275 m atm-cm.

Separability of Agricultural Cover Types by Remote Sensing in the Visible and Infrared Wavelength Regions

The purpose of this study was to determine the statistical separability of multispectral measurements from agricultural cover types: com, soybeans, green forage (hay and pasture), and forest, in one to 12 spectral channels. Multispectral scanner data in 12 spectral channels in the wavelength range 0.4-11.7 μm, acquired on July 16, 1971 for three flight lines, were analyzed by applying automatic pattern recognition techniques. The same analysis was performed for data acquired on August 12, 1971 over the same three flight lines to investigate the effect of time on the statistical separability of agriculture cover types. In subsets of one to six spectral channels, the combination of wavelength regions (where V, N, M, and T denote the visible, near-infrared, middle-infrared, and thermal-infrared wavelength regions, respectively): V, V M, V N M, V N M T, V V N M T, V V N M M T, respectively, were found to be the best choices for getting good overall statistical separability of the agricultural cover types for the data acquired on July 16 as well as August 12. An effort was made to explain these results on the basis of the spectral properties of agricultural cover types. The overall statistical separability of the agricultural cover types was found to be greater for the data of August 12 than the data of July 16 (Table II).

Absorption bands of bacteriochlorophyll types in purple bacteria and their response to illumination.

Abstract 1. 1. Absorption spectra of various species of purple bacteria at 20° and −170° with a high spectral resolution, and spectra of light-induced absorbance changes, occurring upon illumination with light of a relatively low intensity, were measured in the near-infrared wavelength region between 750 and 950 mμ. 2. 2. At least 5 spectroscopically different bacteriochlorophyll types, namely B ∗ 800, B 800, B 820, B 850 and B 890, were observed in Chromatium B ∗ 800, for which the maximum of the absorption band is at a somewhat lower wavelength than that for B 800, was also found in the Thiorhodaceae Rhodothece conspicua and Thiocapsa floridana ; B 820 was also found in Rh. conspicua and in Rhodopseudomonas palustri . All species examined, except Rhodospirilium rubrum , contained B 850 in addition to B 890. 3. 3. In all species, except R. rubrum and Rps. palustris , the absorption bands of either B 820 or B 850 and of B 890 shifted upon illumination towards a slightly longer wavelength. An analysis of the B 850 shift in Rhodopseudomonas spheroides indicated that allumination causes a shift of about 1.25 ± 0.20 m μ and that 25–28% of the B 850 molecules participate in this reaction. It was estimated that in this species the absorption bands of 10–15 molecules of B 850 were shifted per light quantum absorbed at 593 mμ. In Th. floridana and Rth. conspicua there occurred in addition a shift of a band at about 800 mμ towards a shorter wavelength. Lowering of the temperature also effected a shift of the bands of B 820, B 850 and B 890 towards a longer wavelength. 4. 4. The light-induced spectral shifts are interpreted as being caused by conformational changes in the carrier molecules of the bacteriochlorophyll types.

Light-induced spectral shifts in bacteriochlorophyll and carotenoid absorption in purple bacteria

Light-induced absorbancy changes in the near-infrared wavelength region in intact cells and cell free preparations of photosynthetic bacteria have been object of several investigations ( Duysens, 1952; Duysens et al., 1956; Arnold and Clayton, 1960; Clayton, 1962; Vredenberg and Duysens, 1963; Sybesma and Vredenberg, 1963, 1964; Kuntz et al., 1964). An absorption decrease around 870–890 mμ in purple bacteria has been attributed to the oxidation of a reaction center P 890 upon illumination. Recently Clayton (1963) reported in Rhodopseudomonas spheroides a different type of infrared absorption changes. These changes, which are not observed in Rhodospirillum rubrum (e.g. Duysens et al., 1956), could not be attributed to the oxidation of P 890, because of their kinetics and sign at 890 mμ. This paper gives the results of a closer study of the characteristics of these changes in various species of sulphur and non sulphur purple bacteria. In contradistinction to Clayton we conclude that they are not caused by a primary light reaction.