Design, fabrication and evaluation of chalcogenide glass Luneburg lenses for LiNbO3 integrated optical devices

Optical waveguide Luneburg lenses of arsenic trisulfide glass are described. The lenses are formed by thermal evaporation of As2S3 through suitably placed masks onto the surface of LiNbO3:Ti indiffused waveguides. The lenses are designed for input apertures up to 1 cm and for speeds of f/5 or better. They are designed to focus the TM sub 0 guided mode of a beam of wavelength, external to the guide, of 633 nm. The refractive index of the As2S3 films and the changes induced in the refractive index by exposure to short wavelength light were measured. Some correlation between film thickness and optical properties was noted. The short wavelength photosensitivity was used to shorten the lens focal length from the as deposited value. Lenses of rectangular shape, as viewed from above the guide, as well as conventional circular Luneburg lenses, were made. Measurements made on the lenses include thickness profile, general optical quality, focal length, quality of focal spot, and effect of ultraviolet irradiation on optical properties

Proceedings of the Second Airborne Imaging Spectrometer Data Analysis Workshop

Topics addressed include: calibration, the atmosphere, data problems and techniques, geological research, and botanical and geobotanical research

Design and Characterization of Optical Metamaterials Using Tunable Polarimetric Scatterometry

Optical metamaterials are a class of engineered materials with a wide range of material properties and an equally wide range of anticipated applications. This research targets optical metamaterials in two ways. First, the dimensional constraints necessary to bring effective medium theory (EMT) into agreement with the already well-established transfer matrix method (TMM) modeling for a periodic, stratified (metal-dielectric) near-zero permittivity structure were determined. This provided a path to leverage the use of EMT in the design of near-zero permittivity structures and accurately predict its post-fabrication behavior. Second, the first tunable infrared (IR) Mueller matrix polarimeter-scatterometer was developed to capture the full-directional, full-polarimetric behavior of IR metamaterials. Modeling was used to determine the optimal dual rotating retarder configuration to apply to the instrument design, which was subsequently implemented. Free-space measurements corroborated the optimized design with Mueller matrix extractions having less than 1% error. The instrument was then used to measure a unique metamaterial absorber at 5 microns and captured the polarimetric behavior of a surface plasmon polariton resonance as a function of incident angle. Modeling was used to distill the s-polarized and p-polarized reflectance behavior and phase differences in the reflectances that led to the resonant signature in the measured results. As a final step, the measured results were used to predict the reflectance behavior of the material against a series of incident canonical polarization states

Automated thematic mapping and change detection of ERTS-A images

The author has identified the following significant results. For the recognition of terrain types, spatial signatures are developed from the diffraction patterns of small areas of ERTS-1 images. This knowledge is exploited for the measurements of a small number of meaningful spatial features from the digital Fourier transforms of ERTS-1 image cells containing 32 x 32 picture elements. Using these spatial features and a heuristic algorithm, the terrain types in the vicinity of Phoenix, Arizona were recognized by the computer with a high accuracy. Then, the spatial features were combined with spectral features and using the maximum likelihood criterion the recognition accuracy of terrain types increased substantially. It was determined that the recognition accuracy with the maximum likelihood criterion depends on the statistics of the feature vectors. Nonlinear transformations of the feature vectors are required so that the terrain class statistics become approximately Gaussian. It was also determined that for a given geographic area the statistics of the classes remain invariable for a period of a month but vary substantially between seasons

Characterization of microdot apodizers for imaging exoplanets with next-generation space telescopes

A major science goal of future, large-aperture, optical space telescopes is to directly image and spectroscopically analyze reflected light from potentially habitable exoplanets. To accomplish this, the optical system must suppress diffracted light from the star to reveal point sources approximately ten orders of magnitude fainter than the host star at small angular separation. Coronagraphs with microdot apodizers achieve the theoretical performance needed to image Earth-like planets with a range of possible telescope designs, including those with obscured and segmented pupils. A test microdot apodizer with various bulk patterns (step functions, gradients, and sinusoids) and 4 different dot sizes (3, 5, 7, and 10 $\mu$m) made of small chrome squares on anti-reflective glass was characterized with microscopy, optical laser interferometry, as well as transmission and reflectance measurements at wavelengths of 600 and 800 nm. Microscopy revealed the microdots were fabricated to high precision. Results from laser interferometry showed that the phase shifts observed in reflection vary with the local microdot fill factor. Transmission measurements showed that microdot fill factor and transmission were linearly related for dot sizes >5 $\mu$m. However, anomalously high transmittance was measured when the dot size is <5x the wavelength and the fill factor is approximately 50%, where the microdot pattern becomes periodic. The transmission excess is not as prominent in the case of larger dot sizes suggesting that it is likely to be caused by the interaction between the incident field and electronic resonances in the surface of the metallic microdots. We used our empirical models of the microdot apodizers to optimize a second generation of reflective apodizer designs and confirmed that the amplitude and phase of the reflected beam closely matches the ideal wavefront.Comment: Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wav

The effect of herbicides, pesticides, and fertilizers on the optical properties of water

A reflectometer accessory for a spectrophotometer was designed and constructed in our laboratory. Using distilled water as the reflectance standard, the reflectometer was used to measure relative specular reflectance of 0.5M aqueous solutions of K2SO4 and NH4H2PO4 in the 2-12m wavelength region and for 1M (NH2)2CO in the 2-20m wavelength region for infrared radiant flux incident at about 70 degrees and linearly polarized perpendicular to the plane of incidence. Absolute reflectances of the solutions were computed for 70 degrees angle of incidence by using the relative reflectance measurements, one of the Fresnel equations, and the optical constants of water. The optical constants of the aqueous solutions were then computed by applying a Kramers-Kronig phase-shift dispersion analysis to the absolute reflectance spectra. The report provides a description of the instrumentation and the experimental procedures for making the measurements. The relative reflectances, absolute reflectances, and optical constants are presented in graphical form in the text and are tabulated in Appendix I. Spectral signatures characteristic of the solutes are discussed in the text. In addition, further investigations of the optical constants of distilled water were made in that they are related to the investigations of aqueous solutions. The work on distilled water was accomplished in cooperation with Dr. Dudley Williams at Kansas State University. A reprint describing the work is presented in Appendix I.Project # A-030-MO Agreement # 14-31-0001-302

Project Iris: Image reconstruction of the iris spectrally

The basic motivation behind this project is a highly accurate representation of the human iris, to be injected into a virtual model of the human eyeball. A highly accurate brightness level recording can be easily obtained with a high quality digital camera. Color, however, is an entirely different matter. Photography in the traditional sense entertains all sorts of color inaccuracies, mostly related to the chemical process of development. Digital photography presents gamma and metameric problems, since the exact conditions of the capturing event cannot easily be duplicated. However, the spectral radiance of an object can be captured, utilizing a spectrophotometer and reliable light source. In this research, a priori measurements and analysis of the human iris spectral reflectances are performed. Using a spectroradiometer spectral reflectance samples from human iris are taken and this sample set is analyzed using principal component analysis to give a number of basis functions to reconstruct the original reflectance with sufficient accuracy. A color transformation can be built between the signals from a photometric linear digital camera and the weight coefficients of the eigenvectors. Finally, the spectral reflectance can be derived from the digital counts of the camera giving us a highly accurate representation of a human iris

Infrared reflectance measurements of Missouri waters for water quality applications

Students supported: 2 studentsThe relative specular reflectance of laboratory solutions of 3.0 M Sulfuric Acid and 0.5 M Sodium Nitrate was measured in the 2.0 - 20-[mu]m wavelength region of the infrared. The relative specular reflectance of natural samples of (1) acid mine drainage taken from a ditch leading from the Peabody Mark Twain Mine to Hinkson Creek; (2) surface water runoff from an agricultural test plot which had received a 314 lb/acre application of nitrate fertilizer; and (3) an oil sample from the Mexico, Missouri oil release into the Salt River was measured in the same spectral region. The data was collected using a Perkin Elmer E-14 spectrophotometer and a reflectometer consisting of a Cassegrain unit which collimated the radiant flux to about 18 mrad divergence, a sample holder and a Cassegrain condenser for focusing the radiant flux, reflected by the sample, onto the entrance slit of the monochromator. The angle of incidence was 70 degrees. The index of refraction, extinction coefficient and phase difference spectrum throughout the 2-20-[mu]m wavelength region was determined for the mine drainage, fuel oil, sulfuric acid, sodium nitrate and nitrate runoff samples using the relative reflectance measurements, the optical constants of distilled water and an algorithm for Kramers-Kronig analysis. The absolute reflectance spectrum of the alluvium and loess was determined using the relative reflectance measurements, the optical constants of distilled water and the Cauchy equation for reflectance. It is very desirable to make water quality measurements remotely. However before such measurements can be taken the characteristic manner in which aqueous solutions reflect electromagnetic radiation (in the optical properties) must be known. Thus the results obtained from this research are a part of a much larger goal to determine water quality remotely.Project # A-063-MO Agreement # 14-31-0001-382