Performance optimization and light-beam-deviation analysis of the parallel-slab division-of-amplitude photopolarimeter.

A division-of-amplitude photopolarimeter that uses a parallel-slab multiple-reflection beam splitter was described recently [Opt. Lett. 21, 1709 (1996)]. We provide a general analysis and an optimization of a specific design that uses a fused-silica slab that is uniformly coated with a transparent thin film of ZnS on the front surface and with an opaque Ag or Au reflecting layer on the back. Multiple internal reflections within the slab give rise to a set of parallel, equispaced, reflected beams numbered 0, 1, 2, and 3 that are intercepted by photodetectors D(0), D(1), D(2), and D(3), respectively, to produce output electrical signals i(0), i(1), i(2), and i(3), respectively. The instrument matrix A, which relates the output-signal vector I to the input Stokes vector S by I = AS, and its determinant D are analyzed. The instrument matrix A is nonsingular; hence all four Stokes parameters can be measured simultaneously over a broad spectral range (UV-VIS-IR). The optimum film thickness, the optimum angle of incidence, and the effect of light-beam deviation on the measured input Stokes parameters are considered.

Polarization properties and fractional-power analysis of coated and uncoated parallel-slab multireflection beam splitters.

The polarization properties of coated and uncoated parallel-slab multireflection beam splitters are investigated. In a recent study [Opt. Lett. 21, 1709 (1996)] it was shown that the parallel-slab beam splitter is a basic optical component of the parallel-slab division-of-amplitude photopolarimeter. The ellipsometric parameters and the fractional powers for multireflected components generated by this system are analyzed. Interesting new observations with respect to the polarization properties at the Brewster angle of incidence and the distribution of powers among the multireflected components are presented.

Parallel-slab division-of-amplitude photopolarimeter.

A division-of-amplitude photopolarimeter (DOAP) is described that uses a dielectric parallel-slab (PS) beam splitter that is coated with a high-reflectance metal on one side at oblique incidence. The instrument matrix of the PS DOAP is nonsingular, hence all four Stokes parameters can be measured simultaneously over a broad (UV-visible-IR) spectral range. The parallel, evenly spaced, ref lected beams simplify interfacing of the PS DOAP with linear photodetector arrays for both single-wavelength and spectroscopic polarimetry. The PS DOAP has several degrees of freedom that can be controlled for optimum performance.

Maximum rate of change of the differential reflection phase shift with respect to the angle of incidence for light reflection at the surface of an absorbing medium.

The differential reflection phase shift, Delta = delta(p) - delta(s), associated with the external reflection of monochromatic light at the surface of an absorbing medium is a monotonically decreasing function of the angle of incidence ø which is determined by the complex dielectric function epsilon. A new special angle of incidence, denoted by ø(Delta'max), is defined at which the slope Delta' = partial differentialDelta/ partial differentialø of the Delta-ø curve is maximum negative, Delta'(max), and a transcendental equation is derived that determines this angle. ø(Delta'max) differs from the principal angle ø(p) at which Delta = 90 degrees . As an example, ø(Delta'max) is calculated by numerical iteration for light reflection at the air-Si interface for photon energies hv from 1.7 to 5.6eV in steps of 0.1eV, and is plotted, along with the associated maximum slope Delta'(max), vs wavelength lambda. It is noted that ø(Delta'max)>ø(p) at every lambda, a result that may hold in general. Also, for 4.5 > 1 (e.g., for metals in the IR), Delta'(90 degrees ) is a direct measure of the extinction coefficient k = Imepsilon((1/2)).

Reflectance of an absorbing substrate for incident light of arbitrary polarization: appearance of a secondary maximum at oblique incidence.

The reflectance of an absorbing substrate Rtheta(?) is considered as a function of the angle of incidence ? and an incident polarization parameter theta, where cos(2)theta and sin(2)theta give the power fractions of incident radiation that are p-and s-polarized, respectively. Taking GaAs as an example, we find that at certain wavelengths (e.g., 0.248 and 0.620 microm), the R(theta) vs ? curve becomes oscillatory in a narrow range of theta > 45 degrees with an unexpected secondary maximum appearing at oblique incidence. The extrema of the function R(theta)(?) are determined numerically, and their angular positions and reflectance levels are plotted vs theta for GaAs at photon energies of 1, 2, and 5 eV.