[Laser] cheap filters

[Phil Lefever]

At 05:13 PM 6/25/03 -0400, you wrote:
>Anyone have any suggestions on cheap bandpass filters for visible red 
>lasers?  I'm looking for something that would pass 630-700nm, but have 
>substantial attenuation at 850nm.  The reason for this is to get rid of 
>the 850nm line spectrum from sodium lamps.  I'm thinking about cellophane 
>or plexiglass that I might be able to find easily.  I thought I would ask 
>here before I went to the lab via the craft store

A deep red filter should help a lot. If you want to actually know the
spectrum pass band look into photographic filters like the Cokin
made gel system. You can probably find their spectral curves on
their web site.

Another possibility, though more expensive, is the use of Astronomical
light pollution reduction filters. These are more complicated thin film
filters instead of just dyed glass. These can have extreme out of band
attenuation with minimal attenuation of desired wavelengths. A good
choice would be the Orion SkyGlow filter. It will pass about 95%+ at
650nm and will GREATLY attenuate the major lines from both Sodium
and Mercury vapor street lights. Look at www.telescope.com and do
a search on Skyglow Filter. As I said these are fairly expensive but
still less then 1/2 the price of Edmund's LASER band pass filters!

73

Phil