Long- & Short-pass Filters for the Infra-red
Long-pass
and short-pass filters are useful for defining spectral regions or as dichroic
beamsplitters. These are thin film
filters deposited onto Zinc Seleninde, Germanium or Calcium Fluoride substrates.
They are arranged to have a very sharp cut-off.
However, the high reflection region is limited so it is important to
specify clearly the rejection wavelength range required.
Normally high reflection and high transmission wavelengths should be
separated by at least 250nm for effective use in the infra-red.
Cut-off
points can be selected in the range 4 to 10 μm in 0.5μm increments.