Antireflection-structured surfaces for mid-infrared entrance windows

Didier Dubreuil; Erol C. Harvey; Claude Pigot; Nadeem Hasan Rizvi

doi:10.1117/12.317309

21 August 1998 Antireflection-structured surfaces for mid-infrared entrance windows

Didier Dubreuil, Erol C. Harvey, Claude Pigot, Nadeem Hasan Rizvi

Proceedings Volume 3354, Infrared Astronomical Instrumentation; (1998) https://doi.org/10.1117/12.317309
Event: Astronomical Telescopes and Instrumentation, 1998, Kona, HI, United States

Abstract

SubWavelength Structured Surfaces (SWS), by synthesizing effective index of refraction, offer an attractive way to mimic antireflective coating effects. It is of particular interest for some IR materials of high index of refraction such as CdTe or KRS-5. These material are often used for entrance window in cryogenic IR instrument in the 20 microns band. For these materials, multilayer antireflective coatings provide limited performances in transmission, while expected performances of SWS can be very high even for a wavelength range covering both the N and Q atmospheric windows, from 7 microns to 28 microns. The SWS simulates a gradient index layer. Its main parameters are its pitch and its depth. The pitches required depend on the IR material index. For CdTe and KRS5, they are around 3 microns to work in N-band and Q-band and around 6 microns to work only on Q- band, and the depth required is around 10 microns to work till 28 microns. We have tried a new approach to realize these structures by using excimer laser ablation technique. We describe the used technique and our results for different materials such as CdTe, KRS5, CsBr and CsI. Antireflection structured surfaces on CdTe could offer an increase in transmission better than 25 percent at 24 microns. We measured a transmission efficiency of near 96 percent between 23 micrometers and 35 micrometers on KRS-5, and more than 95 percent between 18.5 micrometers and 35.5 micrometers on CsI.

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Didier Dubreuil, Erol C. Harvey, Claude Pigot, and Nadeem Hasan Rizvi "Antireflection-structured surfaces for mid-infrared entrance windows", Proc. SPIE 3354, Infrared Astronomical Instrumentation, (21 August 1998); https://doi.org/10.1117/12.317309

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KEYWORDS

Excimer lasers

Antireflective coatings

Diamond

Laser ablation

Infrared materials

Silicon

Gradient-index optics

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