Beam Dump Makes Sure Your Laser Path Is Safely Terminated

Between hot things, sharp things, and spinny things, there’s more than enough danger in the average hacker’s shop to maim and mutilate anyone who fails to respect their power. But somehow lasers don’t seem to earn the same healthy fear, which is strange considering permanent blindness can await those who make a mistake lasting mere fractions of a second.

To avoid that painful fate, high-power laser fan [Brainiac75] undertook building a beam dump, which is a safe place to aim a laser beam in an experimental setup. His version has but a few simple parts: a section of extruded aluminum tubing, a couple of plastic end caps, and a conical metal plumb bob. The plumb bob gets mounted to one of the end caps so that its tip points directly at a hole drilled in the center of the other end cap. The inside and the outside of the tube and the plumb bob are painted with high-temperature matte black paint before everything is buttoned up.

In use, laser light entering the hole in the beam dump is reflected off the surface of the plumb bob and absorbed by the aluminum walls. [Brainiac75] tested this with lasers of various powers and wavelengths, and the beam dump did a great job of safely catching the beam. His experiments are now much cleaner with all that scattered laser light contained, and the work area is much safer. Goggles still required, of course.

Hats off to [Brainiac75] for an instructive video and a build that’s cheap and easy enough that nobody using lasers has any excuse for not having a beam dump. Such a thing would be a great addition to the safety tips in [Joshua Vasquez]’s guide to designing a safe laser cutter.

37 thoughts on “Beam Dump Makes Sure Your Laser Path Is Safely Terminated

  1. Lasers earn complete terror from me, as in, I will not even consider messing with the high power ones without the full level of precaution.

    I really have no answer or explanation for why people don’t take them seriously. It doesn’t make any sense.

    1. Because they don’t hum ominously and don’t vibrate with constrained power? They are like “oh look, shiny fun beam!”. It takes much thinking before someone realises that even third reflection has enough power to burn out your eyes.

      1. In a physics lecture, the lecturer brought along a CO2 laser to show off. He had it pointed along the front desk facing the side wall for safety. He failed to notice an open text book at the end of the desk that was just in the beam and started smouldering :)

    2. I feel the same regarding microwaves and all the range of effects on what isn’t always a non-linear medium or considered as or is a non-linear medium and the effects. Like heterodyne, pulse train and carrier modulation with demodulation on the target concerns.

      A new concept was reminded by someone asking me a question I hadn’t researched in years regarding use of Nd-YAG lasers versus Holmium-YAG or Thulium lasers. Well reading into the latest lithotripsy methods… I found an excellent analogy of a CW laser is like a drill. A pulse train modulated laser is like a hammer drill. Significantly more effective.

      That’s not getting into other more refined methods of the source effects on materials and minimalist energy requirements for the photons effect or is are some effects due to even more exotic not well known phonon interactions and effects with the photons?

        1. I learned “pulse train” like a generic term for the range of pulse modulation methods of the range of waveforms. Since one can think pulsing typically like PWM or PPM or exotic like more biological roles say like electrophysiology.

    3. This! Complete terror.

      At some old workplace, somewhere very far away in some building edge they had a huge balancing machine for stuff
      larger than 45 t/100000 lbs. For balancing massiv rotors and axial fans and such.

      /me was scared the hell out of it due to its flimsy construction and totally brain dead operating personal (that was the major reason…). /me always kept a distance from it while making assumptions about how fast the load might climb the wall, follow the ceiling, fall down and repeat that path.

      Some things are really scaring.

      1. You don’t need mahoosive machines to create danger.

        I still remember seeing the shrapnel marks in the wall of the server room at Edinburgh University, that were caused by a 12″ hard disk letting go. All around the wall of a 20 foot room, at about waist height.

  2. Interesting solution. I think some lasers might need you to bolt a couple of old Pentium II heatsinks, one either side if you’re gonna have it on long though.

    Not discussed is the laser inadvertently reflecting off things in unintended directions, a simple trick to avoid this is to chalk the end of the beam with some pool cue chalk to stop it from skipping off target.. ;-)

  3. We have 200w rf excited co2 lasers at work. Those things scare the sh#t out of me. Hard finding commercial beam dumps rated to that power level.
    Might have to try this with water cooled cpu block tacked to the outside

      1. The beam is expanded before it hits the galvos then focuses down through the theta lens before hitting whatever we’re marking. Currently we just run the system into a big black steel box with nothing remotely close to the focal plane of the laser. Lets us torture test the new beam lines for accelerated wear to give us an idea of what’s likely to die during extended deployments. Whole thing is just a bit unwieldy is all. Not the end of the world given the chillers and other supporting systems.

    1. An acrylic brick ought to soak up the beam… once. For enough time to hit the E-stop. For something that needs to take the beam continuously instead of an emergency, you’ll definitely need liquid cooling.

    2. Few loops of that copper pipe you use to connect up icemakers with, painted black, one end in a reservoir of potable water, the other end over a cone of ground coffee with your mug under it.

  4. About 20 years ago I worked in a laser lab where we used Ar+-lasers of about 10W (and similar Nd-lasers) and we had several types of homemade beam dumps:

    – graphite blocks (cubes with edges of about 5cm) with a hole of about 1cm in diameter about 2cm into the material. Worked quite well and was not critical when during alignment the beam was moved out of the area of the hole.

    – copper tubing. We took a 90° piece of standard water tubing (about 1″ diameter) mounted to some Al block. The advantage was the rather large hole to hit during alignment. Copper also absorbs at the green wavelengths of the lasers but most of the beam is reflected down onto the Al block. And the curvature of the tube helped also diverging the beam. We didn’t even care to paint them black. So there was some nice green glow from its opening. Since our optical tables had a magnetic surfaces we used switchable magnetic mounts to mount them. No way of accidentally moving them. But can be moved much quicker than something screwed to the table. And since they are really cheap and easy to make you can always have some spare ones.

    – and for low-power reflections we had black anodized Al sheets of about 5cm x 20cm with a small bend (about 160°) along the length (slightly V-shaped) which were friction mounted with three pins to a base with a little magnet. I had dozens of them on my table.

    In my opinion (except for permanent installations and really high power applications like the 200W above) beam dumps should not be over-engineered. Better to have several mediocre ones spare on the shelf than lacking a single perfect one. The opening should not be too small, either, because when making adjustments the beam easily walks a couple of mm.

    P.S. And there is a “golden” rule when working with lasers: no wrist-watches and no rings on your fingers!

    P.P.S. It does not make sense to buy adjustable apertures for a beam dump as considered at the end of the video. I’ve seen too many of them with holes burned into the blades (from less powerful beams even).

  5. Was thinking now there is the Musou black that is the blackest black paint.

    Seems the lining in the container tube can be improved to baffle more of the reflected diffused radiation.

    Wondering if an outer cone would be better like a smaller section of the plumb bob or longer slimmer cone so basically have half cone sections or adjacent equal slopes on the side walls and then the center cone. Seems would be most effective. Like an anechoic chamber basically is what I envision.

    Then something maybe like a one way mirror neutral density filter design or something maybe might improve?

    Collimate the beam to be larger and not so small a duty cycle point effect issue. Like what, why keep the beam so small?

    I’m not an expert in the world of optics, though just invested in a optical workbench to start off the interferometry projects. Like above noted risks and concerns in the comments along with other dangerous planned projects capabilities if not certain what doing well planned like a QC technician pessimist as it gets approving to pass or be released… I am in no hurry.

    Then it’s like… I still want Kanbans dangling above me when I look at the button or something like the procedure in my hand or on the control screen and actually reading to remind me what I can f-up if not already designed monkey f-up proof. I don’t plan to perform any high energy projects soon however… though this is good to know. My ICP or Arc methods will place the sample and then cover. Laser Ablation… I’ll be paranoid and probably do the same.

  6. On a strong laser, how long to melt or warp that plastic end cap, while you align the beam through the hole?

    Seriously… in my youth, I’d do stupid things like use a couple polarizing camera filters to look DOWN the beam and into a Helium Neon laser tube. This eliminated (attenuated most) of the red, leaving an interesting blue glow visible from the plasma arc inside the tube. Hmm… can you see that mirror at the other end? But your mother warned you not to look at the sun or arc-welding with your naked eye, no!

    Be careful and stay safe!

  7. I apologize for askimg here, but can anyone recommend real safety glasses to wear when working with a co2 k40 laser? I have searched online and seen huge price differences and now am very unsure what to trust. Is there a trusted brand among those in the know? Thanks for any recommendations.

    1. For a CO2 laser, just use a decent set of polycarbonate safety glasses. They do not need special tinting as polycarbonate won’t pass 10.6 um. I’ve been hit in the face with a diffuse reflection from a 2 kW CO2 laser at about 2 meters while wearing polycarbonate glasses – not an experience I’d care to repeat, but no eye damage.

      1. Just make sure they are actually polycarbonate (I’ve yet to find any that aren’t) and look for some with really good side protection. A stray beam making its way onto the backside of the lens can still bounce around and into your ‘balls. Doesn’t transmit 10.6 but certainly reflects it.

  8. when i heard the beam dump was for safety, i imagined it was part of a closed loop control system.

    the beam dump would need a sensor in it (which could be tricky) and if the sensor isn’t flooded with enough light then it turns off the power supply. the power supply could be rigged to auto-reset at some rate so that you could use the brief flashes of laser light to aim the thing and you know you got it right when the laser stays on.

    now that’s safety. :)

  9. Don’t worry; if the laser itself doesn’t get you the wiring on that massive transformer will work a treat.

    Treat lasers with the respect they deserve for the deadly light *and* the usual high voltage everybody.

    1. Any self respecting mad scientist has Igors to look into lasers for them. And with their ability to self repair, using organs of questionable origin, no problem – infinite eyes.

  10. So in the movie Real Genius they should have had a beam dump instead of shooting it across town ?

    I thought a beam dump was a floor and a cat….but then that make sense of where hairless siamese cats come from…..😆

  11. When I worked for NCR one of my jobs was to adjust the beam pattern on the first laser scanners in grocery stores. They weren’t LED scanners like today’s scanners but had an actual laser tube. The only way to adjust the internal mirrors that split and directed the beams was to put a piece of onion skin paper on the top glass and stare into it to get the pattern aligned. No one at the company was worried about eye damage. I do remember that cashiers at the time thought the scanners could make them sterile or cause skin cancer.

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