ABSTRACT
Multilayer coatings can be useful for thermal control and thermal display applications. They can be designed to absorb and emit optical radiation very strongly at specified wavelengths. Multilayer tuned infrared absorber/emitter coatings can be applied to fiber optic arrays to form infrared scene projectors. A scene projector absorbs incident laser or electromagnetic energy introduced into the fibers as the subject, and each fiber emits radiation in an infrared wavelength band as an image pixel. The coatings must be robust. During operation, the surfaces of the fibers are cycled to temperatures as high as 260°C. The coating design described here employs thin-film layers of silicon nitride (Si3N4) and chromium (Cr). The coating structure consists of two distinct designs: a lower three-layer coating which absorbs strongly at the 1.06 μm laser wavelength, and a six-layer upper coating which emits strongly in the 3-5 μm infrared (IR) wavelength band. An opaque Cr layer separates the upper and lower designs. The absorption of the three-layer coating is greater than 0.99 at 1.06 μm. The average emittance of the six-layer coating is greater than 0.95 in the design wavelength band.
