Date: Fri, 17 Dec 2010 10:01:46

Author: David Maiullo

Subject: Re: Violet laser pointers and stimulated emission

Post:

Hi All,

According to a gentleman I work with, Dr. Mark Croft, this is his
explanation:

> sounds like stimulsted emission to me
> see
> http://phet.colorado.edu/en/simulation/lasers
> for a simulation
>
> the violet/UV excites (pumps electrons into) a higher energy level
> which decays quiclly to a lower level - the lower level has a much
> longer lifetime and decays with a longer half life emitting green
>
> green light can tickle-stimulate the lower level to depopulate all at
> once hence the green flash and dark line (along which the level is
> depopulated.
>
> the green laser and the second energy level are presumably not
> perfectly tuned to the same energy but the level broadening of both
> must allow a stimulated decay path
> regards mark
>
> precisely what white paper shows this effect - would like to duplicate
>
So, Zeke, what paper (color/type) were you using?

Too cool, these lasers are fun (yet dangerous).

Cheers,
Dave

> I bought a 10 mW violet (405 nm) laser pointer from Amazon. The laser pointer
> does an excellent job exciting a green glow in the dark piece of paper.
>
>
> I also bought a 30 mW green laser pointer. It doesn't make the paper fluoresce.
>
> Actually it does in a weird way.
>
> If the paper is already glowing from the violet laser pointer or an ultraviolet
> lamp, running the green laser dot from the pointer slowly across the paper makes
> the paper glow brighter briefly then go out, leaving a a dark line behind.
>
>
> I figure that this is caused by simulated emission. Thoughts?
>
> Marc "Zeke" Kossover
>


On 12/17/2010 2:19 AM, William Beaty wrote:
>
>
>
> ideas:
> - 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 mirrors.
>
> 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.
>
>
>
> (((((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))))))
> William J. Beaty SCIENCE HOBBYIST website
> billb at amasci com http://amasci.com
> EE/programmer/sci-exhibits amateur science, hobby projects, sci fair
> Seattle, WA 206-762-3818 unusual phenomena, tesla coils, weird sci


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