7 ms·

Why don't welding/cutting lasers add more divergence with built-in optics? Would it hurt performance? It seems like you could add 1 mrad and it would hardly mak

by tlb 2y ago

Why don't welding/cutting lasers add more divergence with built-in optics? Would it hurt performance? It seems like you could add 1 mrad and it would hardly make a difference at the usual working distance, but spread out to a meter over 1 km, so you can't zap people across town.

queuebert 2y ago
Whatever refracts the light will have to stand up to the beam for long periods of time. Maybe it's a materials science problem.
- eru 2y ago
  As long as it doesn't absorb the light, it's fine. Just like the electric cables for your water kettle typically don't get hot.
  - queuebert 2y ago
    Your kettle's power cable is sized to handle the relatively tiny current put into it, but even then it does warm up slightly. Try to run a million amps through it, and it will vaporize. This type of laser carries so much energy that even a tiny fraction of a percent absorption will add up quickly, hence the propensity for injury.
oh_my_goodness 2y ago
If it's a 1-micron wavelength laser with a 60 micron radius spot, the divergence can't be much less than about 5.7 mrad half angle. What makes eye safety tricky is just that 2.5 million milliwatts is a lot of power. Even when you spread it out some.
- cwillu 2y ago
  ‹twitches in metric prefix› 2.5 kilowatts. It's called 2.5 kilowatts. ‹calms down› 2.5 kilowatts is how much power a tea kettle in the UK draws. It's an insane amount of power to pump into a 60 micron point.
  - oh_my_goodness 2y ago
    2.5 billion microwatts.
    - TaylorAlexander 2y ago
      Sure but how many millijoules per day is that?
      - schoen 2y ago
        216 billion.
  - sebastiennight 2y ago
    This seemed like a wild claim (2500 watts for a tea kettle!? As much as a microwave oven in full blast?) so I looked it up. Wow.
    - maldie 2y ago
      Interesting what power do microwaves in US deliver. In EU the regular micros are about 900W range give or take 200W (that is 1500W from wall because microwaves are not efficient machines) but kettles have usually range 2200..3000. So it is obvious why everyone uses kettles. I myselft have 3kW one and it heats 0.35 litres to boiling in 51 seconds. To have similar microwave it would have to be 3000W micro that is 4500W from wall and have not seen that kind of monsters, also regular 1 phase EU socket delivers max 3600W so that limits it also.
      - cwillu 2y ago
        Standard wall outlet in the US is 15 amps, so a maximum of 1800 watts. 20 amp outlets (which can supply 2400 watts) are getting common, but I've seen very few home appliances that actually use the extra amperage (as determined by having a plug keyed for such an outlet).
      - yencabulator 2y ago
- amluto 2y ago
  On the other hand, 2.5kW of light is not outrageous. It’s not drastically higher than some of the larger theatrical lights. (Not that being in a spotlight is pleasant, but it does not permanently blind the actors.) A lot of this comes down to wavelength. Some wavelengths get focused by one’s eye and can concentrate their power in a small spot on the retina. Other wavelengths will be absorbed before they get to the retina and will therefore deposit their power over a larger area and in less sensitive tissue. It can also make a difference if the light is pulsed.
  - ponector 2y ago
    But isn't stage light labeled for consumed power, not emitted power?
    - jaystraw 2y ago
      that's what i was going to say. and while you can use barn doors and lenses to hone the throw (the size of the beam on stage) -- it's not collimated like a laser is. even with parabolic reflectors like par cans. we're talking magnifying glass and the energy at the focal point (minus what the air absorbs for a given wavelength etc)
  - zettabomb 2y ago
    Are you sure that's actually 2.5kW of optical power? Non-scientific lights aren't usually rated by optical power, but by electrical power.
  - deleted 2y ago
    [deleted]
- tlb 2y ago
  I'm not an expert here. But according to https://en.wikipedia.org/wiki/Diffraction-limited_system https://en.wikipedia.org/wiki/Diffraction-limited_system (see last paragraph of the intro) the diameter of a laser beam doesn't impose a diffraction limit on the optics it goes through. You still get the angular resolution you'd expect given the entire aperture of the lens even though the beam is only going through a small area of it.

by tlb 2y ago

queuebert 2y ago

Whatever refracts the light will have to stand up to the beam for long periods of time. Maybe it's a materials science problem.

eru 2y ago
As long as it doesn't absorb the light, it's fine. Just like the electric cables for your water kettle typically don't get hot.
- queuebert 2y ago
  Your kettle's power cable is sized to handle the relatively tiny current put into it, but even then it does warm up slightly. Try to run a million amps through it, and it will vaporize. This type of laser carries so much energy that even a tiny fraction of a percent absorption will add up quickly, hence the propensity for injury.

oh_my_goodness 2y ago

If it's a 1-micron wavelength laser with a 60 micron radius spot, the divergence can't be much less than about 5.7 mrad half angle. What makes eye safety tricky is just that 2.5 million milliwatts is a lot of power. Even when you spread it out some.

cwillu 2y ago
‹twitches in metric prefix› 2.5 kilowatts. It's called 2.5 kilowatts. ‹calms down› 2.5 kilowatts is how much power a tea kettle in the UK draws. It's an insane amount of power to pump into a 60 micron point.
- oh_my_goodness 2y ago
  2.5 billion microwatts.
  - TaylorAlexander 2y ago
    Sure but how many millijoules per day is that?
    - schoen 2y ago
      216 billion.
- sebastiennight 2y ago
  This seemed like a wild claim (2500 watts for a tea kettle!? As much as a microwave oven in full blast?) so I looked it up. Wow.
  - maldie 2y ago
    Interesting what power do microwaves in US deliver. In EU the regular micros are about 900W range give or take 200W (that is 1500W from wall because microwaves are not efficient machines) but kettles have usually range 2200..3000. So it is obvious why everyone uses kettles. I myselft have 3kW one and it heats 0.35 litres to boiling in 51 seconds. To have similar microwave it would have to be 3000W micro that is 4500W from wall and have not seen that kind of monsters, also regular 1 phase EU socket delivers max 3600W so that limits it also.
    - cwillu 2y ago
      Standard wall outlet in the US is 15 amps, so a maximum of 1800 watts. 20 amp outlets (which can supply 2400 watts) are getting common, but I've seen very few home appliances that actually use the extra amperage (as determined by having a plug keyed for such an outlet).
    - yencabulator 2y ago
amluto 2y ago
On the other hand, 2.5kW of light is not outrageous. It’s not drastically higher than some of the larger theatrical lights. (Not that being in a spotlight is pleasant, but it does not permanently blind the actors.) A lot of this comes down to wavelength. Some wavelengths get focused by one’s eye and can concentrate their power in a small spot on the retina. Other wavelengths will be absorbed before they get to the retina and will therefore deposit their power over a larger area and in less sensitive tissue. It can also make a difference if the light is pulsed.
- ponector 2y ago
  But isn't stage light labeled for consumed power, not emitted power?
  - jaystraw 2y ago
    that's what i was going to say. and while you can use barn doors and lenses to hone the throw (the size of the beam on stage) -- it's not collimated like a laser is. even with parabolic reflectors like par cans. we're talking magnifying glass and the energy at the focal point (minus what the air absorbs for a given wavelength etc)
- zettabomb 2y ago
  Are you sure that's actually 2.5kW of optical power? Non-scientific lights aren't usually rated by optical power, but by electrical power.
- deleted 2y ago
  [deleted]
tlb 2y ago
I'm not an expert here. But according to https://en.wikipedia.org/wiki/Diffraction-limited_system https://en.wikipedia.org/wiki/Diffraction-limited_system (see last paragraph of the intro) the diameter of a laser beam doesn't impose a diffraction limit on the optics it goes through. You still get the angular resolution you'd expect given the entire aperture of the lens even though the beam is only going through a small area of it.