Science Shows Green Lasers Might Be More Than You Bargained For

This may come as a shock, but some of those hot screaming deals on China-sourced gadgets and goodies are not all they appear. After you plunk down your pittance and wait a few weeks for the package to arrive, you just might find that you didn’t get exactly what you thought you ordered. Or worse, you may get a product with unwanted bugs features, like some green lasers that also emit strongly in the infrared wavelengths.

Sure, getting a free death ray in addition to your green laser sounds like a bargain, but as [Brainiac75] points out, it actually represents a dangerous situation. He knows whereof he speaks, having done a thorough exploration of a wide range of cheap (and not so cheap) lasers in the video below. He explains that the paradox of an ostensibly monochromatic source emitting two distinct wavelengths comes from the IR laser at the heart of the diode-pumped solid state (DPSS) laser inside the pointer. The process is only about 48% efficient, meaning that IR leaks out along with the green light. The better quality DPSS laser pointers include a quality IR filter to remove it; cheaper ones often fail to include this essential safety feature. What wavelengths you’re working with are critical to protecting your eyes; indeed, the first viewer comment in the video is from someone who seared his retina with a cheap green laser while wearing goggles only meant to block the higher frequency light.

It’s a sobering lesson, but an apt one given the ubiquity of green lasers these days. Be safe out there; educate yourself on how lasers work and take a look at our guide to laser safety.

53 thoughts on “Science Shows Green Lasers Might Be More Than You Bargained For

    1. I’m sure the content is top notch (not a laser person myself). But what a blast from the past that site is, including the language of the remarks on top of the page. Really takes you back to the 90s.

        1. That web site has very poor readability, since it has no styling applied to it. The lines are unreasonably long, and it’s well-known that long lines make for more difficult reading (harder to move your eye to the start of the right line).

          Old and minimal don’t always mean better.

          1. I agree, the line wrapping seems off, something dragging the window narrower isn’t going to solve. I turned the page styling off but that didn’t change anything. Not my default font and type size aren’t the problem because the browser isn’t bring up the horizontal scroll bar I’m not going to bother and summit the URL to the sites that rate accessibility.

      1. Well, it is based on a usenet-newsgroup FAQ and describes itself as a “fluff-free zone”, I am not surprised.
        (not that being based on a usenet-newsgroup FAQ makes it old-school, look at IMDB)
        Seems like good information, so thanks to Shrad for the link.

      2. That’s why it tastes so good :)
        ASCII schematics and drawings have something special
        Besides that, it doesn’t only talk about lasers but covers high voltage, amplifiers, supplies, physics, chemistry, vacuum, mechanics, fluids, integration, general lab experience, and is a collection of knowledge from a vast number of sources… it has been feeding my curiosity since the mid-20’s and I still visit it regularly
        Had some contacts with Sam by email and he is as sympathetic as his website
        I think it deserves a featured here as when I think about it, this is an ultimate hacker’s guide (also covers general repair as the site name hints)

          1. I’ve been wanting to do a general / laser-show laser safety thing for ages. But Josh’s piece on laser cutters is pretty good, so I back-burnered it.

            We could try to do a feature on Sam’s Laser FAQ, but I can’t really think of the angle, except for “here’s an amazing laser resource you should know about”. And I’ve already said that. :)

            Any ideas?

    2. Sam’s is definitely one of the best resources out there! But if you haven’t seen it linked on HaD, that’s your problem, not mine. :)

      For instance, I name-drop in this article: https://hackaday.com/2016/04/18/sciencing-dvd-rw-laser-diodes/, saying “If you want to know everything about lasers in general … you can’t beat (Sam’s)”

      The other place I would go, especially for light-show type stuff, but also for the fact that it’s frequented by professionals in that particular industry who know about safety from an occupational-hazard standpoint, is https://www.photonlexicon.com/forums/

      1. You’re right, it appears in the comments, I was meaning an article in general but was thinking out of my head…
        I’m on photonlexicon too actually even if I’m not an active member anymore… hacked some lasers myself several years ago and I still have some things to do in the field… drawers, you know…

  1. There’s an issue of Scientific American from some time in the 1980’s with a couple of great articles on DIY LASER projects. One is a how-to on building a Mercury Vapor LASER from scratch. Brush up your glass blowing skills and you’ll also need a decent vacuum pump. The other is on things you can put together for a LASER light show, without spending a ton of money, except on the LASER of course. Among the things are mounting a pair of small speakers with hinged mirrors, mounted to make an X-Y beam deflector, and how to make your own diffraction grating by putting many parallel lines of black tape onto white paper, taking a photograph then doing reductions so the final negative has fine enough lines and gaps so a LASER beam will cover several. If one had the photo equipment, at the time that could be cheaper than buying linear polarizers or diffraction gratings.

    Got a couple pairs of polarized sunglasses? Shine a LASER pointer through one at a surface where the spot is visible. If you get more than one dot from both pairs of sunglasses, they’ll work for the next bit. Stack two of the lenses and shine the LASER through. Rotate one lens. Ohhhh, ahhhhh. If you get a single dot through the lens, it won’t work. Circular polarized lenses don’t do this, so nicking a pair of RealD 3D movie glasses is pointless for LASER fun.

    1. “…from the “Scientific American” article by C. L. Stong for June 1974, pages 122-127. The pictures are really all you need, but if you want the text, well, you’ll have to ask your librarian! Not shown in the pictures are the microscope slides cemented over the holes in the end plates. Moving the spark gap to the rear outside corner of the assembly and replacing the rear slide with a first surface mirror increases the power output.”

      http://www.montagar.com/~patj/n2lmnu.htm

      Home-Built Nitrogen (N2) Laser

      http://donklipstein.com/lasercn2.htm

      1. I remember that and someone built one in a chem lab. It is really slick and a simple design. Pulses are short with high power and in the UV if I recall. Use quartz windows.

      2. The one I recall was a tube with angled Brewster windows at the ends. It had a pocket in the mid bottom for the mercury and a couple of extensions on top with electrodes. IIRC there was something about using dry ice to freeze the mercury before pumping the air out. I assume that was so the pump wouldn’t pull mercury vapor out. Once a vacuum was pulled, let the mercury thaw and some would vaporize to fill the tube.

        I do have an old Gast rotary vane vacuum pump. :) Vacuum pumps and vacuum cleaners, the only things that are good when they suck.

  2. I love the video for the way he really gets the demonstration right: showing that the remaining light is actually IR by interposing an IR filter is rock solid. The one thing that’s lacking is an estimate of the leaked IR power. Is it a little or a lot? (It’s surely more than none!)

    But you shouldn’t get getting these beams in your eyes anyway, green or IR. This means paying attention to beam termination or better still, containing the laser in a box. Goggles are designed for preventing the worst in the case of accidental exposure, but shouldn’t be a first line of defense.

    If you want to take all the fun out of playing with lasers, have a read on the FDA’s website: https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=1040.10 and search for “beam attenuator” to discover that any laser above Class I (>1 mW) needs a shutter and that any in Class III (5 mW to 500 mW) need a key, mechanical interlocks, and a means of preventing any possible human eye exposure — i.e. the whole safety thing, not a handheld flashlight-like device.

    My personal rule of thumb is that stuff gets serious above like 50 mW, and I don’t play with anything above 200 mW (where a stray reflection can blind in a jiffy) when I’m tired or lubricated. And that’s for visible lasers. IR and UV creep me out even at low power.

    Don’t look into beam with remaining eye.

    1. I got a 400mW laser for engraving. I didn’t trust the goggles so I built a box with an interlock and monitor the job via webcam inside the box. I thought I was being cautious but this makes me think it’s more like just being sensible.

      1. Cheap webcams are the laserist’s best friend! Not only can they see a little bit better in the IR than we can, they’re also very easily replaced if you shoot one. The ease/price of just putting an opaque box around your laser and tossing a webcam inside makes extreme laser safety extremely accessible.

        Read Josh Vasquez’s “laser safety for laser cutters” piece linked at the bottom of the article. He covers most of the bases, including interlocks. It sounds like you’re doing it right. :)

    2. IR lasers are indeed creepy. I was once testing a 1 kW YAG laser: I’d just set the head on an optical table and was test firing it at about 2 pulse/s at a cinderblock with the full 20 mm diameter aperture (no focussing optics). I hadn’t bolting the head down yet and managed to hook my sleeve on the head and pivoted it about 20 degrees before I hit the kill switch. Every spot on the wall the beam fired at the paint was blown off down to bare concrete, 5 of them in all.

      I promptly bolted the head down and made sure all the interlocks were in place and tested before any more test firing.

        1. I honestly have no idea what’s going on there. Anyone? Burns rust but not your fingers?

          The explanation for the rust removal that I found includes “absorbed by rust, reflected by metal” which doesn’t make me very comfortable. 1000 W IR laser pointed at specular reflective surface?

          If anyone knows in reasonable detail how these things work, let loose, or post a link.

    3. From what i remember playing around with DPSS green lasers, Your typical 5mw green output laser has a 200mw IR laser behind the crystal that does the frequency conversion. I have no clue how much of that power is remaining after the conversion and leaks though crappy or non-existent filters. Pretty much assume that no IR/DPSS laser should be shown directly at someone’s eye.

    1. No, they don’t, because they don’t need it, they do not use DPSS technology like the green ones. They have diode lasers directly emitting the used wavelength, near IR (780nm) for CD and red (650nm) for DVD.

  3. Powerful lasers are awesome and scary at the same time. I did some industrial automation jobs where we used high powered lasers for metal cutting and also laser cladding. These were lasers in the 1kW to 2kW range. Granted they cost over $1 million, but it wasn’t my money!

    The 2kW unit we used was actually an array of diode lasers fed through a fiber optic cable to the head. It was also infrared, which added to the creep factor because all you saw was sparks! These systems were mounted on industrial robots and the whole system was enclosed in light tight booths with wavelength filtered window panes and cameras inside to monitor progress. The doors were electrically locked during operation, the laser had to be shut down and the room air exhausted for a period of time before the doors would unlock.

    We did a destructive test with a sample of the booth wall material 2 feet in front of the laser. The 2kW laser burned a 3/4 inch hole through the wall panel sandwich (18 ga steel, 1/2 drywall, 2 in foam, 1/2 drywall, and 18 ga steel) in 1 minute 20 seconds. At closer range, it would have burned a smaller hole more quickly, but the robot’s safety systems prevented it from getting any closer to the booth walls.

  4. DO NOT LOOK INTO THE FIBER OPTIC CABLE WITH YOUR REMAINING GOOD EYE.

    Use all the same precautions when you working with fiber optic communications equipment. Some of the long range SFP modules can have quite powerful IR laser emitters. If you are using single mode fiber optic cable to go more than a couple of kilometers then the source is probably IR.

      1. I’m pretty sure toslink spdif is using IR as well, probably near-ir in the 860nm ish region. The red you are seeing out a toslink connection is probably the same red glow you see on the IR flood LEDs used for security cameras

  5. “…the first viewer comment in the video is from someone who seared his retina with a cheap green laser while wearing goggles only meant to block the higher frequency light.”

    Why do people STILL feel the need to stare into a light source which is close to the brightness of the sun?

  6. Yeah, the world would be better without the cheap green DPSS, simply due to morons using cheap high power version to blind people and dont care about the risks or do it deliberatly. The cheap are terrible lasers too; unstable lightoutput, sensitive to temperature and shock and manufacturing variations.

    But accually Infrared lasers dont have to be more dangerous, they can be less too. The only real dangerous part is that you cant see where the beam/spot is and the blink reflex will not protect the eye. But the eye dont focus IR as well as green, and the skin is more transparent to IR, so if a IR beam hits skin and other tissue it will spread out more, green on the other hand is absorbed. Put a weak red laser against you thumb and the light will make the thumb glow red, do the same with a green and it will be absorbed, IR is more penetrating than red. They eye is also less sensitive to IR damage, partly due to tissue absorbation and partly to IR will not be focused as hard. Above 1400nm the eyes lens is completely opaque to IR. But a 980nm laser will be able to have double the power of a 660nm and be the same “damage” to tissue.

    But if the laser is strong and focused enough it WILL burn, no matter what wavelenght it is, you just have a slightly higher margin of error for lowpower lasers. And above 10mW you really should be carefull and use eye protection and be real careful of reflection in surfaces. My laserengraver with a blue 3W diode laser have a hood with an orange filter window, and laser protection glasses hanging outside.

      1. Thing is, a beam that passes through the lens gets focused to a very small spot on the retina — that’s what the lens is there for, after all. A beam that’s absorbed by the lens never gets focused, so the burn hazard is more-or-less comparable to the same beam hitting skin or whatever.

  7. I wonder if this also applies to these “15W” engraving lasers from aliexpress (445-450nm). I am thinking about using one on my CNC. I wonder if there’s also few watts of IR emited along with the blue light. That would make using blue blocking glasses quite dangerous.

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