Patent ID: 7177516

Claim:
A low energy optical power limiter device for protecting thermal sensors against input threat laser radiation intended to disable the performance of said sensors in the far infrared spectrum, said limiter comprised of: a multilayered optical power limiter device comprised of a plurality of optical power limiter layers of various thicknesses having progressively lower switching threshold temperatures damage thresholds from an input radiation side to an output side of said device and further having high transmissivity below an energy threshold of incoming radiation, said plurality of optical power limiter layers positioned between an input window substrate layer having an input antireflection coating layer thereon and an output window substrate layer having an output antireflection coating layer thereon wherein the optical power limiter layer contiguous with said output window substrate layer has the lowest damage threshold and switching threshold temperature and is first switched on by said threat laser radiation to become reflective from the highly transmissive state in which said threat radiation is progressively reflected back through the remainder of said plurality of optical power limiter layers for a second pass of said threat laser radiation therethrough wherein the temperatures in each of said layers quickly build up by radiation absorption and switch on all of said plurality of optical power limiter layers essentially instantaneously to provide large optical density in the switched state at a low switching threshold representative of said optical power limiter layer contiguous with said output window wherein said plurality of optical power limiter layers has a high damage threshold representative of said optical power limiter layer contiguous with said input window substrate layer.