Fabrication of Very High Contrast Infrared Polarizers

Laser threats are typically linearly polarized at an arbitrary azimuth. This makes it difficult to implement sensor and personnel protection based on polarization rejection. Addition of a linear polarizer at the aperture removes any ambiguity in the threat polarization state and permits use of rejection schemes based on electric vector orientation. The polarizer must be lightweight, compact, and tolerate very high power. A metal grid polarizer is the only type of polarizer which has potential to meet these requirements in the infrared beyond 3um wavelength. Current production methods for metal grid polarizers use the classical technique of grazing incidence deposition of a metal on photoresist. Contrast of these polarizers is limited to 200:l even at l0 um wavelength where performance is best. Ion beam etching techniques can produce a metal grid with much cleaner geometry and a resulting polarization contrast as high as 50,000:1 at 10 um. In addition to potential use for laser threat protection, this type of polarizer will enhance performance of both active and passive infrared sensor systems. Leonard Research Corporation will investigate fabrication requirements needed for ion beam etched metal grid polarizers to yield very high contrast. Production of this type of polarizer could be accomplished in a Phase II program. Commercial availability of high contrast, low cost, infrared polarizers will lead to a renaissance in infrared sensor design, infrared ellipsometry and FTIR spectroscopy.