Date: Thu, 16 Dec 2010 23:19:39

Author: William Beaty

Subject: Re: Violet laser pointers and stimulated emission


- Try a high-mW red laser as well.
- Or a high-power IR LED held close, or IR source focused w/lens.
- Or use a few-watts IR laser pointer (I think you can remove the IR-block
filter & crystal from a green laser pointer. Not eye-safe though!)
- To increase the contrast, try "charging" the green phosphor under UV,
then put it in your freezer.

I found that if green phosphor paper has adhesive-back, and then is glued
down to a solid surface such as a wall, the solid acts too much as a heat
sink, so the "handprint effect" barely works. With phosphor painted on
objects, ...same problem. It will be far more sensitive to any temp
variations if the green phosphor paper is stretched across supports like a
drum membrane. Possible project: paint an old slide projector portable
screen with ZnS paint. (Visions of green-glowing words appearing like
magic, written by a 1-watt IR laser pointer from across the room.)

I wondered if chilled green phosphor paper could act as a thermal infrared
"film" to make visible images. Perhaps paint the back of the membrane
black. Project a thermal image on the rear while observing the front. I
don't have a germanium lens or telescope mirror, so I couldn't try forming
real images from shapes made from red hot wires etc. Now that I say this,
I realize that I should have tried IR shadows. Opaque white polyethelene
is supposed be very transparent, giving a shadow like a glass plate.
Polyethelene fresnel lenses supposedly work in this application. Maybe a
lathe-turned polyethelene sphere-lens would do. After all, the thermal
wavelength is huge: 1/50 of a mm. Surface roughness should behave as high
polish, as long as the roughness was down below 0.001". I note this same
effect with thermal night vision: a sheet of brushed stainless steel
behaves like a polished mirror. Both sides of aluminum foil seem to be

I wondered if microwave oven standing waves could be seen in the
temperature changes causing the green glow pattern. LN2 could keep the
rest dark, but the "cooked" parts should light up brightly. But my own
oven had a bright light bulb, and I didn't want to disassemble it to
disable the bulb.

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William J. Beaty SCIENCE HOBBYIST website
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