Broadband high-optical-density filters in the infrared.
A new concept for the design of broadband (2-25 microm and beyond) neutral-density filters in the infrared region without étaloning effects is proposed and demonstrated. One important aspect of the technique is to use metallic-thin-film (10-200-nm-thick) multilayer combinations deposited onto different substrates (ZnSe, CdTe, Lexan). Neutral-density filters with optical densities as high as 4 are designed and built in the broadband region (2-25 microm). Another key innovation is the use of ultrathin substrates (~100 nm thick) for elimination of étaloning effects normally present in thick (>0.5-mm) substrates. Neutral-density filters with such ultrathin substrates are also designed and investigated.
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Frenkel
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Zhang