The diffuse fundus reflectance and the spectral transmittance of the swine sensory retina was measured in vivo using intravitreal illumination. Pars plana vitrectomy and intravitreal manipulations were performed on a female American Yorkshire domestic swine. Light from a scanning monochromator was coupled into a fiber optic intraocular illuminator inserted into the vitreous. A 1.93-mm(2) region of the illuminated fundus was imaged from an oblique illumination angle. Multispectral retinal images were acquired for four experimental conditions: the eye (1) prior to vitrectomy, (2) after vitrectomy, (3) after insertion of a Spectralon disk super-retinally, and (4) after subretinal insertion of the disk. The absorption of melanin and hemoglobin in the red wavelengths was used to convert relative spectral reflectance to absolute reflectance. The flux scattered from the super-retinal Spectralon was used to correct for scattering in the globe. The transmittance of the sensory retina was measured in vivo using the scatter corrected subretinal Spectralon disk reflectance. The hemoglobin and melanin components of the spectrum due to scattered light were removed from the retinal transmission spectrum. The in vivo spectral transmittance of the sensory retina in this swine was essentially flat across the visible spectrum, with an average transmittance >90%.

A technique for measuring dielectric tensors in anisotropic layered structures, such as thin films of biaxial materials, is demonstrated. The ellipsometric data are collected in a quasi-monochromatic Mueller matrix image acquired over a large range of incident and azimuthal angles by illuminating a very small area on the sample with a focused beam from a modulating polarization state generator. After the beam interacts with the sample, the reflected and/or transmitted light is collected using an imaging polarization state analyzer. An image of the exit pupil of a collection objective lens is formed across a CCD such that each pixel collects light from a different angle incident on the sample, thus acquiring ellipsometric data at numerous incident angles simultaneously. The large range of angles and orientations is necessary to accurately determine dielectric tensors. The small but significant polarization aberrations of the low-polarization objective lenses used to create and collect the focused beams provide a significant challenge to accurate measurement. Measurements are presented of a thin-film E-type polarizer and a stretched plastic biaxial film.

We describe the development of a label-less ellipsometric imaging microarray reader. The ability of the ellipsometric microarray reader to measure binding of sample to microarray surface is verified using oligonucleotide complementary DNA (cDNA) microarrays. Polarized light illuminates the microarray surface through a glass substrate at an angle beyond the critical angle and changes in the polarization of totally internally reflected light resulting from binding events on the microarray surface are measured. This polarization change is used to measure the thickness of biomolecules bound to the microarray. A prototype ellipsometric imaging microarray reader is constructed and calibrated, and the performance is evaluated with cDNA microarrays. The microarray reader measures changes in refractive index changes as small as 0.0024 and thickness changes as small as 0.28 nm. The optimization of angle of incidence and substrate refractive index necessary to achieve high sensitivity is also described. This ellipsometric technique offers an attractive alternative to fluorescence-microarray readers in some genomic, proteomic, diagnostic, and sensing applications.

Passive multiangular, multispectral, and polarimetric sensing approaches each have unique strengths for the measurement of tropospheric aerosol column abundances and microphysical properties. Current spaceborne multispectral and multiangular aerosols sensors operate at approximately 1 km resolution. Under NASA's Instrument Incubator Program, we are developing an electro-optic imaging approach that will enable adding high-accuracy polarimetry to such observations. To achieve a degree of linear polarization (DOLP) uncertainty of 0.5%, our approach temporally modulates the linear-polarization component of incoming light at a rapid rate, enabling each detector within a focal-plane array, combined with polarization analyzers, to measure the relative proportions of the linear Stokes components Q or U to the total intensity. Our system uses tandem photoelastic modulators (PEMs) within a high-reflectance, low diattenuation camera design. The two PEMs vibrate at slightly different resonant frequencies, leading to modulation of the polarized light at a heterodyne frequency of ~25 Hz. High-speed (1 kHz) readout of the detector arrays samples the output waveforms from which Q/I and U/I are derived. We report on experimental and theoretical analyses of PEM and optical system performance, along with plans for developing ruggedized PEMs capable of withstanding launch and on-orbit stresses.

PURPOSE:To demonstrate spectroscopic retinal oximetry measurements on arteries and veins in swine using intravitreal illumination. Retinal arterial and venous saturations are measured for a range of inspired O2 levels after pars plana vitrectomy.METHODS:Pars plana vitrectomy and intravitreal manipulations were performed on two female American Yorkshire domestic swine. Light from a scanning monochromator was coupled into a fiberoptic intraocular illuminator inserted into the vitreous. The retinal vessels were illuminated obliquely, minimizing vessel glints. Multispectral images of the retinal vasculature were obtained as the swine's arterial blood oxygen saturation was decreased from 100% to 67% in decrements of approximately 10%. Retinal vessel spectra were used to calculate oxygen saturation in selected arteries and veins. Arterial oxygen saturations were calibrated using blood gas analysis on blood drawn from a Swan-Ganz catheter placed in the femoral artery.RESULTS:Oblique illumination of retinal vessels using an intravitreal fiberoptic illuminator provided a substantial reduction in the central vessel glint usually seen in fundus images, thus simplifying the analysis of spectral data. The vessel shadows were displaced from the vessel image simplifying the light paths in the eye. Using a full spectral analysis simplified by the light path reductions, we calculated retinal vessel saturations. The reduction of glint allowed for increased accuracy in measuring retinal vessel spectral optical density. Abnormally low retinal venous oxygen saturations were observed shortly after pars plana vitrectomy.CONCLUSIONS:Retinal oximetry using intravitreal illumination has been demonstrated. As a research tool, intravitreal illumination addresses several difficulties encountered when performing retinal oximetry with transcorneal illumination.

Imaging of retinal blood vessels may assist in the diagnosis and monitoring of diseases such as glaucoma, diabetic retinopathy, and hypertension. However, close examination reveals that the contrast and apparent diameter of vessels are dependent on the wavelength of the illuminating light. In this study multispectral images of large arteries and veins within enucleated swine eyes are obtained with a modified fundus camera by use of intravitreal illumination. The diameters of selected vessels are measured as a function of wavelength by cross-sectional analysis. A fixed scale with spectrally independent dimension is placed above the retina to isolate the chromatic effects of the imaging system and eye. Significant apparent differences between arterial and venous diameters are found, with larger diameters observed at shorter wavelengths. These differences are due primarily to spectral absorption in the cylindrical blood column.

PURPOSE To quantify the reflectance of the swine fundus as a function of illumination angle and wavelength using a novel technique of intravitreal illumination. METHODS Enucleated swine eyes were illuminated with a scanning monochromator coupled to a fiber-optic probe placed in the vitreous at several locations. Intravitreal illumination was used to reduce the effects of extraneous reflections and scatter from the anterior structures of the eye, including glints from the internal limiting membrane and blood vessels. Intravitreal illumination provided different light paths and additional information to apply to retinal reflectance modeling. A 25-mm(2) region of the illuminated fundus was imaged while the angle of illumination was varied over a maximum range of 22 degrees . Multispectral images from areas free of large blood vessels were acquired. The diffusely reflected intensity was integrated over the pupil with a solid angle of 0.028 steradians. The spectral reflectance function was calculated for multiple illumination angles. RESULTS Multispectral fundus image sets were obtained for two enucleated swine eyes by using intravitreal illumination. The fundus spectral reflectance function showed decreasing reflectance with increasing illumination angle, rapid changes in the 430- to 480-nm range, and a fairly consistent reflectance decrease for 480 to 700 nm. CONCLUSIONS Variations in fundus spectral reflectance with change in the illumination angle were found to deviate from Lambertian behavior, varying from Lambertian by 5% across the spectrum in one sample and 20% in a second sample. Intravitreal illumination resulted in markedly decreased extraneous reflections.

Near-angle polarization light scattering measurements of polished surfaces using a Mueller Matrix Imaging Scatterometer are performed and results presented. Muller Matrix Movies are presented to aid in visualization of the multidimensional Mueller Matrix BRDF space.

Polarization modulation in photo-elastic modulators (PEM) driven on and off resonance has been investigated for a commercially available PEM using a high speed infrared (lambda=1550 nm) polarimeter. Off-resonance operation was explored in the hope of finding a slower operating mode than the primary resonance. The primary resonance, used for normal PEM operation, was 5 Hz wide with a Q of 8500. The phase transfer function was well behaved and typical of electrical resonances. Device startup and shutdown had smooth amplitude changes occurring over 1/3rd of a second. The photo-elastic modulator was examined at drive frequencies significantly below the resonant frequency. Driving the PEM with several odd sub-harmonics generated resonance at the fundamental frequency. Three other lower frequency resonances were discovered, but all at an oscillation amplitude more than 12 db below the amplitude of the fundamental resonance. Thus a practical configuration to allow slower operation of the PEM was not found.

Several commercial CD-Recordable disks are exposed to high power laser beam at different exposure doses. Degrees of erasure are characterized for CD-R media using time-domain signals and histograms of data retrieved from the exposed disks.

A non-scanning technique for measuring ellipsometric parameters as a function incident and azimuthal angles is presented. This technique is especially suited to measuring the dielectric tensor of arbitrarily oriented biaxial materials.

Techniques for passive remote sensing of aerosol optical and microphysical properties from space include visible, near- and shortwave-infrared imaging (e.g., from MODIS), multiangle intensity imaging (e.g., ATSR-2, AATSR, MISR), near-ultraviolet mapping (e.g., TOMS/OMI), and polarimetry (e.g., POLDER, APS). Each of these methods has unique strengths. In this paper, we present a concept for integrating these approaches into a unified sensor. Design goals include spectral coverage from the near-UV to the shortwave infrared; intensity and polarimetric imaging simultaneously at multiple view angles; global coverage within a few days; kilometer to sub-kilometer spatial resolution; and measurement of the degree of linear polarization (DOLP) for a subset of the spectral complement with an uncertainty of 0.5% or less. This high polarimetric accuracy is the most challenging aspect of the design, and is specified in order to achieve climate-quality uncertainties in optical depth, refractive index, and other microphysical properties. Based upon MISR heritage, a pushbroom multi-camera architecture is envisioned, using separate line arrays to collect imagery within each camera in the different spectral bands and in different polarization orientations. For the polarimetric data, accurate cross-calibration of the individual line arrays is essential. An electro-optic polarization "scrambler", activated periodically during calibration sequences, is proposed as a means of providing this cross-calibration. The enabling component is a rapid retardance modulator. Candidate technologies include liquid crystals, rotating waveplates, and photoelastic modulators (PEMs). The PEM, which uses a piezoelectric transducer to induce rapid time-varying stress birefringence in a glass bar, appears to be the most suitable approach. An alternative measurement approach, also making use of a PEM. involves synchronous demodulation of the oscillating signal to reconstruct the polarization state. The latter method is potentially more accurate, but requires a significantly more complex detector architecture.

A Laser Diagnostic Technologies GDx Nerve Fiber Analyzer was modified to provide a complete Mueller Matrix polarization image of retinal tissue. Preliminary results demonstrate that interesting retardance, diattenuation, and depolarization features can be visualized.

A new technique for simultaneous multi-angle ellipsometric measurements of anisotropic optical structures such as films used in the display industry is introduced. A very small area on the sample is illuminated with a focused beam which after it interacts with the sample and is polarization analyzed is spread across a CCD. Each pixed collects light from a different angle incident on the sample allowing data collection at numerous incident angles simultaneously. The small but significant polarization aberrations of the microscope objectives provide a significant challenge to accurate measurement A mathematical description of the ellipsometric technique is presented. The optical properties of two biaxial samples, a stretched plastic retarder element used for correcting angle of incident effects in LC displays, and a thin layer of E-type polarizing dried liquid crystal material are measured and maps of the ellipsometric parameters Ψ and ▵ as a function incident and azimuthal angles are presented. Data from both samples are reduced using an iterative algorithm with a biaxial thin film modeling software package to compute all three principle components of the dielectric tensor as well as it's orientation.