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Continuous wave?

nabzim

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I have noticed most laser pointers are being powered with 100% duty cycle (always on) power supplies ( at least most constant current laser drivers that I've seen so far in my research).

What is the reasoning for why lasers are not powered with PWM (at a high frequency so you don't see any flicker) the way that most LEDs are powered?
It seems like we would be getting longer run times out of high power diodes without much heat generated, much-extended battery life, and overall longer diode life.

What gives?!?!?
 



Anthony P

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Many are. It depends on which driver you use. The Black Buck 8M comes to mind, but they may be out of stock.
 

Cyparagon

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Unless there's some obvious piece of light physics I'm overlooking (and would be happy to hear about), PWM is for dimming. Most people have no interest in making the laser appear less bright. The goal is typically the contrary.
 

nabzim

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Unless there's some obvious piece of light physics I'm overlooking (and would be happy to hear about), PWM is for dimming. Most people have no interest in making the laser appear less bright. The goal is typically the contrary.
This is very true. It took me a minute to realize that shorter on-times means less photons emitted, which means less average power and less brightness.
But it still seems like it would be a nice utility to have adjustable laser power. It would be awesome to have a full-sized potentiometer with a knob sticking out of the host, so that you could adjust it without taking apart the laser... especially if one were to build an incredibly high-powered laser laser pointer. You could go from lighting things on fire, to just pointing at things, whenever you want. It would also make it easier to get away without having good heat-sinking, because you just turn the power up to burn stuff temporarily when you want to, and just use it at a lower power if you want to leave it on for a long time.

Now that I think about it, isn't this how most drivers work already? (the kind where people do the "pot mod") it's just that its surface-mounted to the PCB so you can't adjust it without taking it apart...
Aren't the adjustable drivers all already using PWM? (NOT the linear regulator kind like lm317, I'm talking about the buck or boost drivers)
Or do they filter and smooth the output?
 

Cyparagon

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Large lasers make rather poor pointers, even if you were to dial back the power. Not only are they inherently unwieldy, the laser spot is not small and well-defined. The efficiency also goes to sh:)t when you drop a high power diode to low power, since threshold current (which is the minimal current required to begin lasing) scales with laser power. PWM would help the efficiency issue by allowing the laser to operate in an efficient band at a very low duty cycle, but the other problems would remain.

Would a pogostick benefit from the installation of a cup-holder? Yes, I suppose you could argue there are some instances where that would be useful, but most would agree it isn't worth the time, effort, cost, weight, or complexity.
 
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icecruncher

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Large lasers make rather poor pointers, even if you were to dial back the power. Not only are they inherently unwieldy, the laser spot is not small and well-defined. The efficiency also goes to sh:)t when you drop a high power diode to low power, since threshold current (which is the minimal current required to begin lasing) scales with laser power. PWM would help the efficiency issue by allowing the laser to operate in an efficient band at a very low duty cycle, but the other problems would remain.

Would a pogostick benefit from the installation of a cup-holder? Yes, I suppose you could argue there are some instances where that would be useful, but most would agree it isn't worth the time, effort, cost, weight, or complexity.
All excellent points, but the one I think you missed was also the price.

You can build a very nice lower power laser pointer, in most colors, for much less than the cost of the high power AND without the added cost and additional issues with chopping the power back.

Its not usually worth the added convienence.
 




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