Don't use a green laser in the cold!

Hi! Earlier, I have shown how a green laser pen stops working, when it is freezing cold. I saw no output, but it may still have been able to fry my eyes. I will test it for invisible output in this video. And what about those lasers, you are meant to put in your garden to decorate your house with? Will they be problematic at a freezing cold night? Let's find out! Laser beams are always an eye hazard. Especially the invisible ones in this video... Wear laser safety googles that protect your eyes against all emitted wavelengths. And... dont't lick the frost. Let us start off with a control test. How does the green laser pen perform when it is at room temperature? I will point the beam at a laser power meter and let a spectrometer look at the dot to see what wavelengths the laser emits. I really wanted to use this 50 milliwatter but it has an issue with the button or a loose electrical connection. When warm it only works with the button half pressed down. When freezing cold I can't get it to work at all. I will have to use this 5 milliwatter in stead. There we go. Immediately, I spot two safety issues. It is much stronger than the under 5 milliwatts on the label. And it emits invisible infrared light. The classic 808 nm and 1064 nm from green DPSS lasers. Granted, this is not emitting that much 808 nm. I don't think it is totally unfiltered in the infrared. It is just poorly filtered... The 50 milliwatter is emitting more infrared, but useless for the next test, where I will freeze the laser. With the 5 milliwatter cooled down let us confirm that it is not emitting any light - as shown in a previous video. Well, it is not emitting green as it is supposed to do. With my eyes, I don't see this odd violet light. Because it is invisible infrared light. Like the light from your remote control, which the camera clearly can see too. I can only see this light if I use an infrared detector card. Actually, with the spectrometer set up why don't we test the wavelength of remote control light? It is centered around 930 nm. As were all remotes I tested. Interesting. My camera will pick up weak 930 nm light. But not strong 980 nm light from this infrared laser. So we now know my camera will pick up the 808 nm from the pump diode inside the green laser But not the 1064 nm from the crystals. After warming up for a while the green laser gradually starts emitting more and more green light as the crystals inside start converting the infrared to green. The crystals are only efficient at the right temperature and when hit by the right infrared wavelength. Let's cool the laser again and get some numbers on how it performs cold. There we have it. 3 milliwatts of only infrared output. No green and no 1064 nm infrared. And not even 808 nm infrared like the warm laser. When cold it is emitting a shorter 800 nm infrared. I explain why the wavelength of diode lasers is temperature-dependent in another video. 3 milliwatts. Not really a lot, is it? I believe I have something more alarming... This garden decoration laser also features a green DPSS laser. In Denmark, these are typically used around Christmas to decorate houses on the outside with red and green laser dots. Meaning the laser could be standing outside on a freezing cold night... The manufacturers seem to be somewhat aware of the issue. Inside the heatsink - - otherwise meant for keeping the green laser cool in hot weather - - they put a resistive heating element. With this, the green laser can be warmed up to perform well even at a frost-clear night. But did they remember to add an inexpensive infrared filter? To keep the green laser from emitting infrared laser light as it heats up? Here's a quick test on the spectrometer. The red laser is taped over and the warm, green laser shows very little infrared leakage. This looks like the spectrum from a well-filtered DPSS laser. Good. What happens when it is cold? All right, the cold laser is now turned on. What will we see? Argh, no! Do you see that? Let me remove the grid lines to make it more visible. And turn off the studio light. *Sigh* This is basically a strong, infrared laser when turned on in the cold. 800 nanometers like the cold pen - just much stronger. I have measured it to be around 40 mW of infrared in a Patreon video. After a few minutes, the heating element - and the room temperature - - has heated the laser enough for it to start lasering in the green. However, the 808 nm leakage is still there. Why was it not showing in the test of the warm laser? Then the obvious hit me: Diffraction. There's a double-axis diffraction grating in front of the laser to split the single beam into hundreds. The longer the wavelength, the more the beam is spread. But there are several orders, and since the 1064 and 532 nm are harmonics, their orders will overlap, while the 808 nm is somewhere between. So in this measurement the probe is in a spot where the two harmonics overlap, while the 808 nm is going past the probe. Since there are hundreds of beams and some diffusion in the glass aperture - - there are places, where all three wavelengths can be detected. Especially when condensation on the aperture diffuses the beams even more... With a filter that blocks visible light and lets infrared pass the infrared 808 nm radiation is also visible to the camera. The conclusion is clear. Never ever look into a laser! Even when it appears to not be working at all - or only sending out weak, red light - - it could be sending out a lot of intense, invisible, infrared light. Thanks to my awesome patrons for helping out with the expensive but well worth it spectrometer. I wouldn't have it without your support. If you want to help me keep going with the videos too I have a link for my Patreon page in the description under the video. Thank you! Thanks for watching. I have links for more videos on the subject in the description Including tests of laser safety glasses failing to protect against infrared. And don't forget to subscribe for even more videos. Bue for now!

Channel: Brainiac75

Views: 2,128,268

Rating: 4.9063835 out of 5

Keywords: laser, laser pointer, laserpointer, green, infrared, 808, 1064, 532, nm, nanometers, wavelength, safety, glasses, goggles, test, experiment, science, fun, interesting, beautiful, educational, learning, garden, decoration, diffraction

Id: 9tOcUyakk0Q

Length: 9min 0sec (540 seconds)

Published: Sun Aug 30 2020

Reddit Comments

[u/Scumbag1234]

Just don't buy cheap lasers from China, they don't have proper infrared filters. Better green laser pointers will still stop working in the cold since phase matching doesn't work then but the infrared light will still be filtered out.

[u/Ansiremhunter]

Yeah, high powered lasers may seem cool... but they can be dangerous. I got a wickedlaser for Christmas once and it worries me with how powerful it is, I thought it would be awesome to own and do stuff with.

[u/ryangood12]

Ice is nice!

[u/Reinardd]

How does that work?

[u/dumpface69]

How do you remove the color all together? How do I make a blue laser less visible?