Effect of temperature on DPSS Laser (image heavy)

It was cold out today so I brought a cheapie green over to my girlfriends place to show her something we were talking about.
DPSS: Diode Pumped Solid State lasers use an infrared diode to pump a crystal that "halves" the wavelength of the light from 1064nm to 532nm and doubles the frequency.
This setup is very precise and if anything changes, it loses efficiency.
My camera picks up Infrared as kind of purple but the dot (to my eyes) is invisible.
Yet another reminder of how dangerous DPSS lasers can be if you are only using goggles effectively blocking 532nm light.

Only infrared, no visible dot

Same as before, was a little confusing until I realised the camera could see something that I couldn't


Finally a bit of green dot peeking through

From here it really picked up.


Remember, this is only a "5mW" laser pen, yeah, it may be overspec but it shows just how much infrared light is let through even if there is no green.
Even if your high powered green laser shows no light:
IT IS STILL DANGEROUS!
Hope you enjoy

-Auto

Do you have a LPM by any chance? Also, Where are you reading the temp from and how are you controlling it?

I was reading the temp from the black part of the host ~3/4" from where it meets the silver end.
I don't have a LPM.
I let the laser warm up slowly (so outside temp matched inside temp) by
1. Outside for 10 minutes
2. Between the screen door and the inside door (closed) - 10 min
3. Same as before but inside door was left open 1" - 10 min
4. Inside the house but against the inside door - 10 min
5. Inside, laying on the counter - 10 min
6. Inside, laying beside the computer.
I took all measurements within ~15 seconds of removing the laser from the tested temperature area.

*edit* The original idea was to take the pics on a white background but they were all overexposed at the end so I had to start over.

its actually the green reacting with the red in the carpen. go hit an orange street safety cone or some red felts do this as well. . it isn't only 405 and 445 that flourese.

michael

No, there was NO dot when I looked at it.
The carpet is brown, when I shone it at the white cupboard in the first test, there was the same "violet" dot on the camera but no dot visible to the eye.
The only reason the camera can "see" the dot is that it can pick up infrared. Any "night shot" camera does it better than this one.

ah, thats a better explanation. it is the ir from your laser. because of the colder temp the green didn't come out. but this is usually at way lower temps than what your thermometer is showing. very interesting....

but just for fun you should still go light up some red felt or orange safety cones.

michael.

Actually I literally just tried it on a "Tide" box that is sitting beside the washer, 405nm fluoresces quite well on it and yup, it goes a brilliant orange with 532nm too

Funny how I noticed the same thing today.
Now that it's cold, some cheap greenies of mine start off (almost) IR only, and then
the green light first appears after a couple of seconds, and then it gets brighter
as the whole thing slowly warms up.
In the summer they came on full power almost instantly.

The one that I used to demonstrate this just went nuts today.
The beam WAS visible in a lit room.
Now, it surpasses the 1.6W 445 in terms of beam brightness.
It is easily burning light colored paper (yellow post its) but probably won't last very long now.
80mW+ burner for ~$5.25?
Yes please!

Interesting. have you tried with more powerful pens (like 10 and 15mW?) they have smaller/none heat delay.

I'd be worried about condensation if they are worth very much.
Apparently the crystal in them is hydrophilic (water absorbing) so it could cloud and screw up your good laser.
I was actually doing this to see if I could use a DPSS laser in an outdoor, unmanned signaling application.....Nope, guess I'll have to stick with either a 445 or a 405.

AUTO XX said:

Remember, this is only a "5mW" laser pen, yeah, it may be overspec but it shows just how much infrared light is let through even if there is no green.

Click to expand...

To be honest, i think it doesnt show -how much- IR light there is at all. Sure, we can see that there is -some- IR coming out of the laser, but how sensitive to IR is the camera? How much power is actually in that purplish spot? 1 mW, 10, or even 100 mW?

If you have a thermal LPM it would be easy enough to actually measure it, since that dot looks small enough to fall onto a sensor.

AUTO XX said:

I'd be worried about condensation if they are worth very much.
Apparently the crystal in them is hydrophilic (water absorbing) so it could cloud and screw up your good laser.

Click to expand...

That's true for 473nm DPSS, because LBO is hydroscopic, and it doesn't really cloud or anything, the crystal just absorbs moisture until it crumbles into powder, and it takes a fair amount of time, but it happens. I've got 532nm crystal sets I've exposed to air for long amounts of time and they still work fine. And usually the coatings protect the important bits of the crystal.

Edit: Or so I was told/read, in case I'm wrong.

Benm said:

If you have a thermal LPM it would be easy enough to actually measure it, since that dot looks small enough to fall onto a sensor.

Click to expand...

Good point, I can use the same thermal sensor as is in the previous pics with a piece of black paper in front of it right?
Saw that on a "lpm for <$50" thread here somewhere...
I'll do that tonight when I get back (and the laser is cold again)

You should be able to use any thermal sensor really. The light leaking out is probably 808 nm that is well absorbed by virtually all black coatings and paints. But even if it is 1064 nm, you get some indication of power, even if the albedo of your sensor is not specified that far into the infrared. You could get a mis-estimation by a factor of 2 or so, but nothing like the factor of 1000 or so for 'hey, i can see that on my camera!'.

The setup I used was the same little blue thermal sensor as in the pics, 1 piece of toilet paper saturated with black sharpie (only a dot, not the whole thing) left to dry and hung in front of the sensor.
With a bigger thermal sensor (the bigger one is backlit and has a red laser indicator) I quickly checked the starting temp of the
Laser: 53.2*F
The laser was ~3" away from the tissue +/- 1/8"
Tissue temp was pretty stable around 68.5*F (ambient) before I tested
after almost 2 minutes on, the temp of the laser came up to ~60.5-60.8*F
after 20 seconds and a little less than 2 minutes the temp on the tissue sensor stayed around 82-83*F
No green dot throughout.
That has to be around 40-45mW of infrared isn't it?
I'll have to look it up but I was surprised there was such a change in temperature.
I'll be a little more cautious with this pointer ( not that I wasn't before)


*edit http://laserpointerforums.com/f42/simple-laser-power-meter-using-ir-thermometer-26341.html

**Edit#2 My red laser pointer (DX 200mW) is only about 165mw and then I burned a hole in my tissue when I fiddled with the focus a bit
Sometimes its better not knowing ^_^