Abstract

Coherent multiple-beam interference in a tilted parallel-plane thin dielectic slab leads to a differential transmission phase shift Δ_t between the p and s linear polarizations, hence such a slab (of an optically isotropic material) acts as the simplest possible nondeviating retardation plate¹. However, a fundamental limitation of this basic device is that quarter-wave retardation (QWR), i.e., Δ_t = 90°, is not attainable using a single uncoated slab. Here it is shown that this limitation is lifted if the slab is coated with a thin film of transparent material of different refractive index. All of the reflection and transmission properties of such transparent bilayer membranes, or pellicles, are studied in detail. These membrane retarders are better suited for the IR and require operation at high angles of incidence. Some of the material systems tested for this application include BaF₂ and ThF₄-coated Ge and a-Si:H layers. A unique design produces dual-QWR in transmission and reflection and uses a BaF₂-a-Si:H membrane at 10.6 μm wavelength and 82° angle of incidence. It exhibits reasonable tolerance to small errors or shifts of film thicknesses, angle of incidence, and wavelength.

© 1995 Optical Society of America