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optical optical decoupler

Decouple the human eye from light
  [vote for,

When working with powerful lasers, the threat of instantly blinding oneself, or permanently damaging ones vision is a constant source of hesitation and distraction. Goggles are available for various wavelength ranges, but no goggles cover all ranges, and it is unclear what their maximum wattage rating is even at the rated wavelength.

Inexplicably, the only ways to make sure you don't do this is to view your work using a camera and monitor, which leads to a loss of precision, and stereo.

What is needed is a simple, lightweight way to take your eye out of the line of fire using no electronics.

The eyes are blocked by blinders suspended two inches from the face. Dished mirrors rest against the cheeks, receiving light and sending it to the backs of the blinders. Finally, lenses close to the eye flip the image and assist the eye in focusing on the rather near blinder backs.

The user only ever sees a projection of anything, but more importantly, dangerous light is always traveling away from the eye.

fishboner, Dec 24 2013


       When laser light is dangerous it is because of its intensity, not because it is monochromatic or coherent. The "screen" in front of the eye, upon which you reflect stuff, needs to be adjustable in terms of how much light it absorbs/reflects. If it reflects enough to allow mostly-ordinary seeing of things, then it would also reflect a dangerous amount of intense laser light.   

       Therefore this Idea appears to be fundamentally unworkable if no electronics is involved, measuring and rapidly adjusting for light-intensity (or doing the standard camera/monitor thing).   

       Perhaps a simpler solution would be to install many very bright lights all through the work area, such that the NORMAL light-intensity is as dangerous as the lasers you would be working with --and then just put on a welder's mask. It nicely reduces the intensity of light that reaches the eyes, and with the whole workplace lit-up thoroughly, you will see ordinary stuff just fine.
Vernon, Dec 24 2013

       I wasn't aware viewing a beam's projection upon a matte surface was just as harmful as the beam entering your eye.
fishboner, Dec 24 2013

       a pair of cameras and mini screens on a pair of goggles would be easy enough. That would work. This idea wouldn't.   

       The other problem, is that there are many lasers that you can't see... so your normal aversion to bright light won't work. The screen-goggles will work here too.   

       The best defense is to know what you're doing, and pull the appropriate $10 goggles out of the bag.
bs0u0155, Dec 25 2013

       Yes, reflections make a laser safer, but it's not an absolute thing. If the visor is reflecting sufficient light to enable you to see the general background, it will reflect sufficient laser light to damage the eye.   

       And the appropriate goggles tend to be more like $50-150 bucks, I use them a lot at work for a really intense LED light source (less focused but brighter than most lasers) but still, you're right. Since you can buy them with selective light filtration, you can still see everything else well enough and just block the beam.
MechE, Dec 25 2013

       //The best defense is to know what you're doing, and pull the appropriate $10 goggles out of the bag.//   

       Is there no maximum rating on those goggles? You can just take a direct hit from a laser of any power, as long as the wavelength is covered?
fishboner, Dec 26 2013

       Yes, welding-mask filters come in different grades of protection. You will need to use the grade that is appropriate to the laser intensity that you are working with.
Vernon, Dec 26 2013

       It depends on the glasses, the ones I play around with are OD7+ (optical density, it's a log scale, so .0000001 transmittance, and they apparently can't test past OD7, so it might be even better) in the wavelengths of interest. That's about the highest you're going to find. So unless you're playing with a 50kW laser, they'll protect your eyes from a direct hit.   

       And if you do manage to stand in the way of a 50kW laser, eye damage is not going to be your largest concern.   

       Reflection, on the other hand, drops the beam strength about one order of magnitude for most black surfaces (90% absorption), possibly two (99% absorption) for certain extreme black optical coatings.
MechE, Dec 26 2013

       //.0000001 transmittance, and they apparently can't test past OD7, so it might be even better//   

       That must be wrong (I mean that they can't test past OD7). Several methods spring to mind:   

       (1) Normal photographic emulsion will register an image in a thousandth of a second or less from daylight via a lens. I imagine a powerful laser beam would register an image in microseconds. So, timed exposures on the order of a few seconds to a few hours via the filter would give you measurable ODs up to maybe 10 or 11.   

       (2) A photomultiplier counts single photons with decent efficiency, and has a noise of maybe 100 photons per second. A watt of laser power is something like 10^18 photons per second; the PMT would be good down to 10^3 photons per second of less, giving a measurable OD up to 15.   

       (3) If the filter is homogeneous, measure the OD of half the thickness; then you know that the OD of the full thickness will be twice that.   

       (4) etc etc.
MaxwellBuchanan, Dec 26 2013

       If you are working in an application with a specific laser, specific goggles are sufficient, unless the laser is malfunctioning, in which case, your narrow range goggles would simply give you a false sense of security. The worst part about them is, by definition, you cannot see the beam you are working with.   

       Now if you are, say, aligning separate heat synced crystals to an IR pump, goggles really become an expensive and tedious way to still come up short, safety-wise, especially when you consider experience makes most users less safe, not more.   

       A full-range means of protection against all specular reflection would be a safer bet.   

       //Yes, reflections make a laser safer, but it's not an absolute thing. If the visor is reflecting sufficient light to enable you to see the general background, it will reflect sufficient laser light to damage the eye.//   

       If what you're saying is that in the event of a spectral reflection, a tiny fraction of the damaging light still enters the eye, I would agree, and I would call that a feature. This is probably why matte coatings are common in labs. Not that it would be hard to sense and trigger the screen to flip up. The user would still be safe because the beam would be hitting his cheek reflectors, not his eyes.
fishboner, Dec 26 2013

       Don't ask me, optics isn't actually my specialty. It may just be that they can't measure selective wavelengths past OD7. All I know is that I have had multiple optical filter vendors tell me that no one can measure past OD7, and this corresponds with the fact that the glasses I was looking at were rated OD7+ in the target band, rather than say 7.5 or 8.   

       (Oh, and three doesn't work, since most filters are surface coatings).
MechE, Dec 26 2013

       No, I'm saying that no matter what you do, you are going to have a damagingly bright spot an inch in front of your eye. If you can see the background, the diffuse reflection itself will be dangerous.   

       Lasers, except pumped lasers, do not malfunction out of spectrum, and if your'e using pumped lasers you should be using glasses that protect against the pumping wavelength as well as the target.   

       Also, the proper glasses for any given use are the ones that leave the beam visible but safe. Which is why they are available in a range of blocking powers.
MechE, Dec 26 2013

       //except pumped lasers//   

       All lasers are pumped. And there are more wavelengths to guard against than pumping and destination wavelength.   

       //The diffuse reflection itself will be dangerous.//   

       In the context of an otherwise un-diffused momentary specular reflection into the naked eye, I think this idea is rather novel. Regardless, a simple threshold sensor and a quick actuator to flip-up the projection surface would solve this.   


       If the matte reflector were swapped for a mirror, this is exactly what would happen. The cheek reflectors send the light to the screens at a 45 degree angle, so the light would end up on your forehead.   

       This brings to mind what might be an important distinction. When you look at a laser dot on a matte surface, there are still angles at which the light appears more intense than others.   

       My idea is really a lot like a shoebox sun viewer, but meant only for seeing the sun for a duration roughly equivalent to that of the blink reflex. The rest of the time it's a camera obsura in stereo.
fishboner, Dec 27 2013

       I'm sorry, I used the wrong term, I meant frequency doubled lasers.   

       All other frequencies that might be emitted are non- collimated and much less intense.   

       And a perfect diffuse reflective surface would return light in a perfect hemisphere, with no angles of reflection being greater than another. However, since there is no such thing as a perfect diffuse surface, you will see better and worse angles.   

       And a sun viewer is a camera obscura. The trick is that it lets in only a very small fraction of the incoming light, and spreads it sufficiently that it's safe for the human eye. That's possible because the sun is an exceptionally bright source. It can be possible with a laser, as long as the beam is diffused well back from the point of impact. However, it is not possible to do it with a high intensity laser at the same time as with the room background, the contrast levels just don't allow it.
MechE, Dec 27 2013


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