[Laser] Filter Material.

[Tom Becker]

I was ready to suggest that you use a pair of Rosco (or similar) gels - 
a pair of specific products yield a pretty-dark short-IR filter - but 
reconsidered.  If you need a filter for a motion detector you probably 
need one for longwave IR - or, more likely, a lens.

The detectors I have use lenses to illuminate a pair of detectors 
differentially.  Although the plastic material of the lens is surely 
frequency-selective, its principal function is lensing, not filtering.  
Simply replacing your 'filter' with, say, 35mm film or Roscos might well 
make the detector motion-blind.

FWIW.


Tom