Very interesting black light+CRT+red laser phenomenon.

[tung]

Hey guys...I'm new to the forum and I was thinking this "phenomena" I observed a few years ago using a 5mW 650nm pointer would be great as the subject of my first post,so here it goes.I was playing around with the pointer one night inside with all lights off except for a "tube style" black light.In the same room I had an old,non-working console TV ,the screen of which was glowing greenish yellow if I recall correctly.To my astonishment,wherever I shined the pointer on the screen would "unglow" the phosphors...weird huh? Anyone have a clue as to what was going on? How about possible applications for said effect? Anyways,HELLO LPF members! :thanks:

 

[Gryphon]

I remember something like this some time ago where i think a ir laser (or mabye it was the ir leds in a cameras night vision mode) was used to de-glow a gitd material. i think it was something along the lines of de-flourecsing or something like that because of the long wavelength

 

[aryntha]

Actually, this phenomenon is used to detect invisible lasers... I had to buy some ZnSe reagent compound to test for a beam on some of my IR lasers.

What you do is expose the ZnSe phospor to light, and then shine the laser at it - the beam (if present) will 'de-glow' the phospor, showing a dark spot among the light.

I'm not sure of the action behind it - i'm sure someone else could join in and educate us all, but yeah, it's certainly a known thing and used to detect invisible beams.

 

[flogged]

Good question. How long would the phosphor remain dark after shining the laser on it?

So.. UV light caused the chemicals on CRT plate to undergo luminescence. Often they absorb radiation at one frequency, then convert to another, usually lower frequency. It's possible a red laser will cause the CRT phosphor glow at IR frequencies.

Perhaps the phenomenon is 'secondary emission' (no, not stimulated emission.. haha)

I did find this:

The image would be retained until erased by flooding the scotophor with a high-intensity infrared light or by electro-thermal heating

from this - 'dark trace' CRT :
Direct-View Bistable Storage Tubes - Wikipedia, the free encyclopedia

 

[tung]

Well,what I saw was that the laser brought the phosphors back to ground state so the black light caused them to begin glowing again as soon as the red laser light subsided...hey,thanks alot for the input guys even though my vision of mass fortunes aquired from this "discovery" are now annihilated,haha!

 

[rev0]

This is awesome!!

I just tried it with my old Tek 2205 analog oscilloscope, charged it up with my PHR with no lens, and hit it with a 780nm 100mW CD-RW laser.

Here's a pic (sadly I don't have any video cams even close to sensitive enough to capture it):



When I shoot it with the IR laser, it actually gets brighter for a second, then dims out. I guess it's speeding up the photon emission of the phosphor, and the result is that it leaves a dim spot since most of the energy is gone.

 

[lazeerer]

I found this video pretty cool. Kind of weird as well. I dont have a CRT monitor but i tried it with a glow in the dark Star that i have and it works just like the video.

kUteUH7mz0A

 

[LaZeRz]

lol nice

 

[Benm]

It's a fairly wellknown phenomenon, and happens with many phosphorescent materials (glow in the dark stuff, crt tubes etc).

The exact explanation is not that easy as in involves some quantum mechanics: Material phosphoresce because the transition between a higer and lower energy state is 'forbidden'. Due to that, the transition time is very slow, resulting in the afterglow effect.

When you apply light at a longer wavelength, you can push molecules from the forbidden state to a slightly higher energy state, which allows them to revert to ground state readily because this higher energy state does not have a forbidden state change to ground. That state change may or may not result in the emission of light by itself.

The theoretical foundation may be a bit diffcult to grasp if you aren't into this material, but the observations are explained very well - there is no mystery, but the effect remains cool to obvserve

 

[mod101]

Interesting stuff, did you sometime study quantum mechanics or is this just some random knowledge you have stored away.