Video: Don't use a green laser in the cold!

[Ed.Kloonk]

 

Does a green laser pointer stop working when it is cold? Or does it turn into an invisible laser? That is nice to know for safety reasons if you are using a green laser pointer to point out stars on a frost-clear night.
And what about those decorations lasers for your garden? Are they safe at a freezing winter night? Time to find out in this video!

[bson]

I don't see anything on whether the IR light emitted is coherent or not, but I only watched to the end of the laser pointer demonstration.

[Daixiwen]

If I remember correctly at one point he uses an IR detector paper and the light seems to be focused on a small point, so I guess this means the light is coherent?

[Kleinstein]

For the danger to the eye it does not matter if the light is coherent. It is the highly focused intensity from a small source that makes is dangerous. Having the power meter at some distance mainly looks at one bright spot.

Those green lasers got better - some 10-20 years ago when it started with cheap green lasers from China, there were quite a few without the filter.

If the laser does not work right at cold temperature, why let it run at all. The electronics should have some temperature sensor to protect against over-temperature. So why not just turn it off below freezing , when it is not working properly.

[dmills]

No real surprise to anyone who understands how a frequency doubled YAG laser works.

In particular look at both the YAG absorption spectrum around 808nm, the temperature dependence of the wavelength of the pump diode, and the thermal phase matching of the dispersive harmonic generator crystal (Often the biggie).

Real frequency doubled lasers generally have thermal controls for both the pump and the SHG crystal (As well as the laser medium itself),  not least because the SHG is exposed to completely insane power density and tends to survive the abuse better if heated.

That laser pen will likely have a diode 'driver' that is really a crude as fuck current source, literally think two transistors and two resistors, and no thermal sensing at all.

[ebastler]

Why is this in the "dodgy technology" section? I would be very surprised if the laser is specified to operate at sub-zero temperatures. So it probably works as advertised/specified.


 

[Cerebus]

Why is this in the "dodgy technology" section? I would be very surprised if the laser is specified to operate at sub-zero temperatures. So it probably works as advertised/specified.

You clearly haven't watched the video or you wouldn't be saying that.

[ebastler]

Why is this in the "dodgy technology" section? I would be very surprised if the laser is specified to operate at sub-zero temperatures. So it probably works as advertised/specified.

You clearly haven't watched the video or you wouldn't be saying that.

I fast-forwarded through it. What did I miss?

[Cerebus]

The laser 'decoration' designed and sold to be used outdoors in a cold Nordic country that, while having a heater to make the YAGiness work in the cold, still emitted significant IR radiation while it was warming up. This is something that people point at their houses (i.e. uncontrolled outdoor use of a moderately powerful IR laser). I think that qualifies as dodgy.

[ebastler]

Ahh, OK; thank you! Spotted the "warning notice" at 5:04 now, which does indeed state that it can be used at temperatures down to -30°C. I concur with "dodgy" then...

[Stuart Coyle]

Why is this a problem. It never gets that cold anyway. Hi from Queensland, Australia.

[eeviking]

Why is this a problem. It never gets that cold anyway. Hi from Queensland, Australia.

Yep global warming will soon have fixed that. We barely get any snow in the winter anymore.

[Ed.Kloonk]

[ebastler]

Ha ha. That video is a painfully lame joke. Made it through the first two minutes and regret every second of it.

[Ed.Kloonk]

Ha ha. That video is a painfully lame joke. Made it through the first two minutes and regret every second of it.

 

"Bloody Hell!"

[Ultrapurple]

Early in the first video we are advised to wear safety glasses to protect against "all emitted wavelengths".

Hmmm, glasses that block VLF to gamma rays ... nope, can't find any on eBay   

[Ed.Kloonk]

Just use the X-ray glasses you used as kid.

[anovickis]

Just use the ole duct tape and strap a brick on your head

[LaserSteve]

The 808 nm pump diode drifts in wavelength 0.20 nm / Deg C, that is generally not the problem, in fact, depending on the diode, cooling it may shift the wavelength just enough to INCREASE the pump adsorption, depending where it is on the lasing medium's adsorption curve,    The KTP frequency doubling crystal is cut using X-ray diffraction for orientation and a cheap one has a roughly +/- 20 degree operating temperature region or the efficacy fades to zero.  The phase matching angle (critical for frequency doubling)  is  very temperature sensitive for type II phase matching.   So cooling it detunes the pump diode, but detunes the crystal far worse.   

In large lasers we cool the diode, and heat the doubling crystal to an optimal phase matching temperature.

BAD VIDEO.

Steve

[Someone]

Why is this a problem. It never gets that cold anyway. Hi from Queensland, Australia.

The detuning mentioned above works in both directions, running a cheap DPSS laser continuously (or in extremely hot conditions) will have a similar effect of shifting the wavelengths until there is no visible output.

[schmitt trigger]

I watched the video. Twice.
Just to listen to the guy say: “Bloody Hell”. 

[Ben321]

Does a green laser pointer stop working when it is cold? Or does it turn into an invisible laser? That is nice to know for safety reasons if you are using a green laser pointer to point out stars on a frost-clear night.
And what about those decorations lasers for your garden? Are they safe at a freezing winter night? Time to find out in this video!

A green laser pointer doesn't turn into an IR laser if it's properly made. For one, it will have an IR-blocking filter in the beam path that will absorb any IR light that leaves the frequency doubler crystal. For another, the frequency doubler crystal always absorbs a certain amount of IR light (about 5% absorption for 532nm DPSS lasers), regardless of its temperature. If it's too cold to convert the beam from IR to green, it will simply absorb the IR light with no output. Conservation of energy says this energy must go somewhere, so it's turned into heat. The energy converted to heat is the same amount of energy normally converted to green light, which is about 5% of the IR beam that hits the frequency doubler. This means that regardless of the temperature you are operating the laser in, that frequency doubler crystal will pass about 95% of IR light, and that IR light always gets absorbed by the IR absorbing glass at the output of the laser pointer.

The only thing that can be dangerous in a green laser pointer is if the manufacturer didn't put an IR absorbing glass block at the output of the pointer. And that danger is one that will exist in equal severity at ANY temperature.

[Cyberdragon]

The point of the video is that most cheap lasers don't have filters. The average consumer doesn't understand how green lasers work and would be at risk of looking at it when it stops making visible light.

[Ben321]

The point of the video is that most cheap lasers don't have filters. The average consumer doesn't understand how green lasers work and would be at risk of looking at it when it stops making visible light.

They might think it's broken so they would look in the end to see what's wrong with it. Is that what you're saying?

[Cyberdragon]

The point of the video is that most cheap lasers don't have filters. The average consumer doesn't understand how green lasers work and would be at risk of looking at it when it stops making visible light.

They might think it's broken so they would look in the end to see what's wrong with it. Is that what you're saying?

Yes, the average human is dumb and knows nothing of laser safety.