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Two-color imaging by the use of a patterned optical filter directly bonded to a HgCdTe focal-plane array is demonstrated. The optical filter is spatially patterned, by multilayer lithographic techniques, to provide multicolor response in the midwavelength infrared by the use of a single substrate.

The behavior of codeposited thin films of ZnSe/LaF(3) and Si/ZnSe has been investigated. Mixed ZnSe/LaF(3) films are polycrystalline with intermediate compositions with moderately high compressive stress (1500-2000 kg/cm(2)). Mixed Si/ZnSe films are amorphous with intermediate compositions with low compressive stress (<1000kg/cm(2)). Optical properties of the ZnSe/LaFcm(3) system vary monotonically with composition, but those of the Si/ZnSe system do not, which is explained by the possible chemical reaction of the two species.

An ultrahigh-Q, tunable optical filter with a FWHM bandwidth of 41 MHz is demonstrated. The filtering is produced by nondegenerate phase conjugation through four-wave mixing in atomic-sodium vapor. The filter is observed to have a maximum quantum efficiency of 4 x 10(-3). However, degenerate phase-conjugation experiments in sodium suggest that a quantum efficiency of greater than unity can be attained on a cw basis.

Rugate filters are optical thin film interference structures with sinusoidal refractive index profiles. Two-wavelength reflection filters have been fabricated by codeposition of SiO(2) and TiO(2). Composition modulation was monitored and controlled using quartz crystal rate controllers. The resulting filters exhibited two well-defined stopbands. Microscopic examination revealed that the structure is glasslike without pronounced thin film microstructure.

A method for depositing patterned infrared thin film spectral filters directly onto substrates at low temperatures (200 degrees C) is described. Energetic deposition methods (ion-assisted and laser-assisted) were used to avoid heating the substrates, while a multilayer photoresist lift-off technique was applied to pattern the structures. The process produced durable films capable of surviving harsh processing conditions. This is a promising method for depositing patterned coatings directly onto infrared focal plane detector arrays.