Video: Don't use a green laser in the cold! - Page 1
Forum section: electronics / general

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: August 30, 2020, 06:25:10 pm
content: Quote

author: bson
author_rank: Unknown
timestamp: September 03, 2020, 10:32:58 pm
content: 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.

author: Daixiwen
author_rank: Frequent Contributor
timestamp: September 04, 2020, 08:09:29 am
content: 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?

author: Kleinstein
author_rank: Super Contributor
timestamp: September 04, 2020, 10:49:54 am
content: 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.

author: dmills
author_rank: Super Contributor
timestamp: September 04, 2020, 10:08:44 pm
content: 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.

author: ebastler
author_rank: Super Contributor
timestamp: September 05, 2020, 09:12:40 am
content: 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.

author: Cerebus
author_rank: Super Contributor
timestamp: September 05, 2020, 02:30:51 pm
content: Quote from: ebastler on September 05, 2020, 09:12:40 amYou clearly haven't watched the video or you wouldn't be saying that.

author: ebastler
author_rank: Super Contributor
timestamp: September 05, 2020, 03:34:37 pm
content: Quote from: Cerebus on September 05, 2020, 02:30:51 pmI fast-forwarded through it. What did I miss?

author: Cerebus
author_rank: Super Contributor
timestamp: September 05, 2020, 03:41:02 pm
content: 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.

author: ebastler
author_rank: Super Contributor
timestamp: September 05, 2020, 03:59:40 pm
content: 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...

author: Stuart Coyle
author_rank: Contributor
timestamp: September 07, 2020, 10:01:03 pm
content: Why is this a problem. It never gets that cold anyway. Hi from Queensland, Australia.

author: eeviking
author_rank: Regular Contributor
timestamp: September 11, 2020, 12:47:07 pm
content: Quote from: Stuart Coyle on September 07, 2020, 10:01:03 pmYep global warming will soon have fixed that. We barely get any snow in the winter anymore.

author: ebastler
author_rank: Super Contributor
timestamp: September 17, 2020, 07:09:13 pm
content: Ha ha. That video is a painfully lame joke. Made it through the first two minutes and regret every second of it.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: September 17, 2020, 09:19:29 pm
content: Quote from: ebastler on September 17, 2020, 07:09:13 pm"Bloody Hell!"

author: Ultrapurple
author_rank: Super Contributor
timestamp: October 06, 2020, 09:41:26 am
content: 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

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: October 06, 2020, 10:11:34 am
content: Just use the X-ray glasses you used as kid.

author: anovickis
author_rank: Contributor
timestamp: February 26, 2021, 09:17:40 pm
content: Just use the ole duct tape and strap a brick on your head

author: LaserSteve
author_rank: Super Contributor
timestamp: March 05, 2021, 11:37:01 pm
content: 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

author: Someone
author_rank: Super Contributor
timestamp: March 06, 2021, 09:06:08 pm
content: Quote from: Stuart Coyle on September 07, 2020, 10:01:03 pmThe 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.

author: schmitt trigger
author_rank: Super Contributor
timestamp: March 07, 2021, 02:22:14 am
content: I watched the video. Twice.Just to listen to the guy say: “Bloody Hell”.

author: Ben321
author_rank: Frequent Contributor
timestamp: April 25, 2021, 12:28:09 am
content: Quote from: Ed.Kloonk on August 30, 2020, 06:25:10 pmA 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.

author: Cyberdragon
author_rank: Super Contributor
timestamp: April 25, 2021, 12:37:37 am
content: 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.

author: Ben321
author_rank: Frequent Contributor
timestamp: April 25, 2021, 12:40:44 am
content: Quote from: Cyberdragon on April 25, 2021, 12:37:37 amThey 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?

author: Cyberdragon
author_rank: Super Contributor
timestamp: April 25, 2021, 12:45:34 am
content: Quote from: Ben321 on April 25, 2021, 12:40:44 amYes, the average human is dumb and knows nothing of laser safety.

author: Ultrapurple
author_rank: Super Contributor
timestamp: April 27, 2021, 11:01:35 am
content: Other than noting the fact that I took this photo (ie it's notme), I make no comment.

author: ebastler
author_rank: Super Contributor
timestamp: April 27, 2021, 03:02:13 pm
content: That is a big box and a big warning sign for a class 2 red laser.(I sure hope it's only class 2, otherwise the warning sign would be misleading those whom it aims to warn...)