Re: Polarization of IR

[Stanley A Dodds <dodds@ruf.rice.edu>]

As others have noted, Polaroid and related dichroic polymer polarizers
work by selective absorption and re-radiation of the incident light.
For reasons I do not know, this process is not independent of
wavelength, so material optimized for visible light may not work in
the IR or UV ranges.

The only spectral data that comes to hand is from the Edmund optics
catalog, which shows essentially complete transmission beyond 800nm
for one of their glass-mount polymer polarizers.

If one wants to use this type of polarizer, the cure is to insert IR
absorbing material before the diode, or use a detector which is not
sensitive to IR. The first solution is probably easier.

> I assume your setup consists of a light source + polarazer + analyzer
> + the diode which reponds well to IR". You are turning the analyzer but
> the reading from the diode remains the same. Strange. Perhaps your diode
> receives more light from somewhere else than what comes throught the
> P + A. Nicole prisms are as good in the near IR as in the visible. I am
> less sure about this for the common polarizing sheets.