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Why are lasers inefficient? Is it because of the heat lost during lasing? Why couldn't there be thermocouples or turbines in parts of the cooling circuits to extract something out of that heat?

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Use of heat from almost all electronics and devices conflicts with the need to keep it cool. The higher temperature the more energy you can get from the waste heat, but almost all devices perform worse at high temperatures too. In terms of why lasers couldn't do closer to 100% conversion of energy into photons, I'd like to know that as well. So would Lockheed Martin I imagine :-P –  AlanSE Jul 29 '11 at 21:47
    
Maybe this should be re-titled 'Are lasers inefficient?' or 'How efficient are lasers?' Given the answers below... –  Nic Aug 3 '11 at 17:30
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up vote 9 down vote accepted

Not all lasers are inefficient. Infrared diodes are quite efficient. This paper shows 64% electrical to optical conversion efficiency: http://www.jdsu.com/ProductLiterature/paper_hipower_910_980_laser_diodes.pdf

An argon gas laser on the other hand is quite inefficient.

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In fact this makes red laser diodes the #1 most efficient way we know of to turn electricity into visible light energy! More efficient than fluorescent, more efficient than LEDs, etc. If only green and blue lasers were as efficient as red, then lasers would be the best energy-efficient way to light your home! (Of course you would need diffusers!) –  Steve B Jul 30 '11 at 1:38
    
@Steve - green lasers are the most efficient light source in terms of lumens/watt, albeit mostly because of the definition of a lumen! –  Martin Beckett Jul 30 '11 at 2:38
    
This is surprising. Your answer would have significant implications on the relativistic rocket problem. Provided that the fuel to electrical energy conversion wasn't bad, it could make sense to power a super long distance spaceship by such infrared diodes en.wikipedia.org/wiki/Relativistic_rocket –  AlanSE Jul 30 '11 at 2:56
    
@Martin Beckett -- What kind(s) of green lasers have high wallplug efficiency? –  Steve B Aug 3 '11 at 3:43
    
@Steve B - wallplug efficiency? Probably none, certainly not frequency doubled YAG / diode! The way a lumen is defined a green light gives you a lot of lumens/watt, which is a bit of marketing spin for green laser pointers –  Martin Beckett Aug 3 '11 at 4:20
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