A Mueller matrix imaging polarimeter is used to acquire polarization-sensitive images of seven different manmade samples in multiple scattering geometries. Successive Mueller matrix images of a sample with changing incidence and scatter angles are used to develop a Mueller matrix bidirectional reflectance distribution function for the sample in one plane of measurement. The Mueller matrix bidirectional reflectance distribution functions are compared, and patterns are noted. The most significant data for the scattering samples measured occurs along the diagonal of the respective Mueller matrices, indicating significant depolarization effects. Reduced depolarization data in the form of the average degree of polarization (of exiting light) for each sample is examined as a function of changing scattering geometry. Five of seven manmade samples exhibit an inverted Gaussian profile of depolarization with changing scattering geometry, the shape of which may prove useful for measuring sample properties (e.g. roughness) and for classifying or categorizing samples in a remote sensing scheme. Depolarization differences for each sample in response to changing incident polarization states are also examined, and a new metric, the degree of polarization surface, has been developed to visualize all such data simultaneously.
A new technique for precise focal length measurements by use of a hologram is presented. The hologram is used in first order diffraction to emulate the reflective properties of a convex spherical mirror when performing null tests with a phase-shifting interferometer. The hologram, comprised of concentric reflective rings (much like a Fresnel zone plate), is written lithographically and offers a higher degree of precision, at lower cost, than its spherical mirror counterpart and many other potential measurement techniques.
We present a method for designing and testing a null corrector for use with scatterplate interferometry on a large conic mirror. The null corrector in a scatterplate interferometer must maintain OPD of less than 1/2 wave over a finite field size for optimal fringe visibility. Our design uses an aspheric diamond-turned mirror (DTM) to exactly cancel out the spherical aberration of the surface under test. The DTM has the additional benefit of being useable in other types of interferometers for testing of the conic surface in a null condition. Low power refractive elements correct field aberrations over the finite aperture of the scatterplate. The null corrector can be certified using another smaller DTM or a computer generated hologram (CGH). This design has the advantages of being small in size, less expensive than designs using spherical surfaces (due to the small size of the null-correcting mirror), useable with other interferometers, and easy to align.
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