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I need to build supply for ~20 laser diodes (~150 mW each), and the question is why can't we just use a constant current power source for each of them?

A similar question for pulsed mode operation: if I would need, let's say, 50 ns pulses, is it correct that I just need to stabilize the current in these periods or is it again more complex?

Can it work this way: We start from, let's say, a 1.5 V supply, use a FET to connect diode to the supply for 50 ns and sense the peak current. Then we slowly increase the supply until we reach the required peak current. Will that work?

Any practical experience? Any comments on the last paragraph?

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    \$\begingroup\$ You'd have to provide more information on a specific laser diode as there are various types. Also "stabilizing" current in 50ns pulses isn't easy. \$\endgroup\$ – Mark Feb 13 '11 at 1:16
  • \$\begingroup\$ These are simple ones salvaged from DVD-RW's. \$\endgroup\$ – BarsMonster Feb 13 '11 at 2:08
  • \$\begingroup\$ You should be able to use a simple constant-current supply to power them. What issues have you been having? \$\endgroup\$ – Connor Wolf Feb 15 '11 at 10:34
  • \$\begingroup\$ I don't have issues yet, just want to understand what is the proper way of driving laser diodes close to their power limit without killing them. \$\endgroup\$ – BarsMonster Feb 15 '11 at 13:42
  • \$\begingroup\$ from my research for the laser cutter i would love to make, constant current or current monitoring is what you will need in the power supply. It depends on your application but both will work with laser diodes. \$\endgroup\$ – jsolarski Feb 15 '11 at 15:05
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Can it work this way: We start from, let's say, a 1.5 V supply, use a FET to connect diode to the supply for 50 ns and sense the peak current. Then we slowly increase the supply until we reach the required peak current. Will that work?

Yes it will work, but if it gets too much current you may burn it out, to little current and it will not lase. Max current is usually 10 to 15 percent above its min lase current.(depends on laser)

some good info here and an interesting chapter here and full table of contentsthey also have some driver references and schematics

I learned a lot from that site about how to drive some re-purposed red laser diodes that I had laying around.

I personally would start off with the lowest current possible, move it up till it lases and then calculate 10% above lasing current and make that your safe constant current, pulsed current can be higher.

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The problem with most laser diodes is that there is significant variation from both part to part variation, and also over temperature. This combines with a secondary issue, which doesn't apply to most other semiconductors, in that there is a possible failure mode through optical damage to the mirror surfaces if laser power is too high - this can cause damage way before any thermal damage to the semiconductor material itself.

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    \$\begingroup\$ +1. This is exactly why laser diodes for communications have integral photo-diodes so that the optical power can be controlled in a feedback loop. They also often have integral thermistors so that the temperature can be regulated with the addition of a Peltier cooler \$\endgroup\$ – MikeJ-UK Feb 16 '11 at 10:57

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