i am more than skeptical about the whole idea.
1) two lasers, one 100mw cw, the other pulsed, 200mw peak, 50% duty. given that the frequency is higher than the given 30hz, say 100hz to be on the safe side, both lasers will appear exactly the same bright. your brain isnt even involved here, the light is integrated in each single receptorcell. the individual receptors on your retina are "driven" with 25hz, give or take. that means they only give one signal each 0,04s. the pigment in the cell, which is decomposed by the photons energy, "sums up" the total energy from a 0,04s period. therefore its simply not possible to see any difference between the pulsed and cw laser. if thats not enough for you, there is even more processing involved, directly behind the individual receptors, even before the eye-nerve, way before the brain.
2) you cant really push the laserdiode (much) higher in pulsed than in cw.
the limiting factors are degration and "catastrophical optical damage" (COD). degration is mainly because of heat (because then impurities and errors in the die do more damage). in a sled, the heatsinking is low and temperature is high. in a regular, naked diode, the thermal path is inefficient, with such tiny surfaces and thermal masses. if you would cool your die perfectly, in theory, it would not make any difference if you pulse or cw the die.
much effort is taken to make our hosts good heatsinks, have a look at the krytons for example. thats a mile away from what the diode has to survive in a sled. its far from the theoretical goal, but good enough, for me.
so in our application, COD is the limiting factor. much more in reds, less in 405nm diodes, its a bit more complicated with these. COD happens in extremely short durations. remembering from sam's laser faq, its at least(!!) down in the ns area. so if we pulse our diode with 100ns (which is ridiculously high, but much slower than the COD time), it would die at the same poweroutput as if it was driven in CW. simply, because when you turn it on in cw with 500mw output, it would be dead in less than 10ns. it doesnt matter that you planned to turn it off after 100ns, in this example.
3) the lasersource *must* be pulsed in an optical drive. simply because it wouldnt write anything useful in cw. sure, it would *burn* a nice ring into the disk.. ;-)
4) even if you design your pulsed laser in a way that the diode isnt outputting more than in CW (which means that average pulsed power isnt higher than cw power), you have more stress on the die. compare to igort's deathchamber for testing diodes. sure, its really low "pulsing", minutes of on-off, to maximise the thermal stress. but the idea is the same.
5) when your pulsed driver fails, it may put the whole pulse-peak current on the diode. instant death.
6) a pulsed laser will in many cases look the same bright, but be more dangerous on your eyes. probably no big enhanced risk when pulsing with such high rates though.
7) but, finally, a positive note: in some cases (depending on pulsewith and material) it may burn better. at least theoretically, i doubt it would even be measurable. imagine a really thin foil, which is burned through in a single high-power pulse. in lower power cw, the thermal radiation from the foil may be just good enough to keep the temperature under the damage-temperature.
so.. no, i wont get me a pulsed driver. there are interesting things to do with it, though. scanners are obvious, but you could as well build something similar into a pointer. a green and red laser in one host, both pulsed, do a yellow (still) dot. it would form a red-green striped line when waved over a wall.
so, as a question from serious curiosity: what will you do with a pulsed laser/pointer?
manuel
