Abstract: Novel rotation sensors are disclosed, sensors with a temporal resolution of one measurement per rotation. A transparent or absorbing substrate can be coated with a transparent thin film to produce a linear response in reflectance versus angle of incidence over a certain range of angles. The best results were obtained when the incident light was s-polarized. For example, a Si substrate coated with an SiO.sub.2 film was used in constructing a reflection rotation sensor. Experimental results and an error analysis of this rotation sensor are presented.

Abstract: A division-of-amplitude photopolarimeter based on conical grating diffraction includes a diffraction grating and at least four photodetectors. An incident light beam is directed at the grating at an oblique incidence angle .PHI. and the grating grooves are inclined at an arbitrary angle .alpha. with respect to the plane of incidence. Each of the photodetectors is positioned to intercept one of the diffracted orders and may be an area array detector if spectropolarimetry use is desired. Polarizing means may be inserted in the paths of one or more of the diffracted orders. A division-of-amplitude photopolarimeter based on planar grating diffraction includes a diffraction grating and at least four photodetectors; the grating is placed in the conventional spectrometer orientation with its grating grooves perpendicular to the plane of incidence.

Abstract: An apparatus and method for the measurement of at least one parameter of the state of polarization of a light beam is described. The apparatus includes only a photodetector and no other optical elements. The detector surface is partially specularly reflecting and intercepts the light beam at an oblique angle of incidence. The absorbed fraction of incident radiation produces a corresponding electrical output signal that is detected and from which the at least one parameter of the state of polarization can be determined. The detector may also be rotated to modulate the electrical output signal to determine the elliptic polarization of light except for handedness. A two detector ellipsometer is disclosed wherein light reflected from one detector is absorbed by the second detector and the entire system is rotated.

Abstract: A photopolarimeter for the simultaneous measurement of all four Stokes parameters of light. The light beam, the state of polarization of which is to be determined, strikes, at oblique angles of incidence, three photodetector surfaces in succession, each of which is partially specularly reflecting and each of which generates an electrical signal proportional to the fraction of the radiation it absorbs. A fourth photodetector is substantially totally light absorbtive and detects the remainder of the light. The four outputs thus developed form a 4x1 signal vector I which is linearly related, I=A S, to the input Stokes vector S. Consequently, S is obtained by S=A.sup.-1 I. The 4x4 instrument matrix A must be nonsingular, which requires that the planes of incidence for the first three detector surfaces are all different. For a given arangement of four detectors, A can be either computed or determined by calibration.

Abstract: To measure characteristics such as density and particle-size distributions of a medium that interacts with light, a polarimeter simultaneously develops all 16 elements of the Mueller matrix by modulating polarized monochromatic light with a quarter-wave retarder operating at a predetermined frequency before transmitting it to the medium and then modulating the light leaving the medium with another quarter-wave retarder which operates at a frequency five times that of the predetermined frequency of modulation of the light transmitted to the medium. The light is electrically detected and provides a signal which may, by Fourier analysis, be broken into 25 terms. The coefficients of those 25 terms, by relatively easy calculations, provide the 16 elements of the Mueller matrix. An electrical element is provided for optically simulating the rotation of a quarter-wave retarder.