Two embodiments of a multilayered low energy optical power limiter device
are disclosed which protect thermal sensors against laser threats in the
far infrared spectral region. One limiter device has multiple layers in
order from the incoming radiation side an antireflective coating layer, a
window substrate layer, a layer of chalcogenide, a germanium substrate
layer, a layer of vanadium dioxide (VO.sub.2), a window substrate, and an
antireflective coating layer. As incoming radiation energy increases, the
VO.sub.2 layer will heat up and change from an unswitched transmissive
state to a switched reflective state. The excessive energy past the
switched state is reflected back through the germanium and chalcogenide
layer and is absorbed quickly therein so that these layers also heat up
quickly and are switched almost simultaneously with the VO.sub.2 layer to
provide high optical density at a low switching threshold temperature
with high damage threshold. The second embodiment further adds a second
VO.sub.2 layer between the input antireflective coating layer and window
substrate layers to reflect high radiation energy immediately.