Instructables

Making a green laser pointer a little bit safer

I use a cheap, allegedly less than 5mW, green laser pointer to point things out in the night sky at public astronomy events.  Unfortunately, recent NIST tests show that a lot of green laser pointers generate a lot of extra visible and infrared light.  The infrared one can do something about.

I ordered a 9.5mm IR cut (not IR pass!) filter from an ebay seller.  It was $7, shipped, for a pair.  Direct from China, of course.
 
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Step 1: Testing the filter

Trust but verify.  Once the filter came, I had to check to ensure that the filter was doing its job.  Fortunately, these days, most of us have infrared sources around, namely TV remote controls, and infrared detectors, namely phone cameras with inadequate infrared block filters.  I made sure that my Galaxy S2 phone's front camera clearly showed the infrared LED pulsing very brightly on my TV remote.  Then I put the filter that came in the mail over the lens.  And now the LED was almost invisible--just a dim, dim pulsing shade of white showed up.  Wouldn't have seen it were it not pulsing.  This isn't a quantitative measurement, but obviously it was blocking a lot of infrared.  

I also made sure that it didn't matter which side up the filter was pointing.  One side of the filter had a shiny coating.  Both seemed equally good at blocking the TV remote's infrared LED.  But just to be safe, I was going to use the shiny side on the laser pointer side (because one normally puts the shiny side of a filter on the side of the source).