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Green laser surgery

I’ve obtained a Green laser module from DealExtreme (sku.26887) that was kinda broken on arrival, so it had to disintegrate for the sake of curiousity.
One plus of this module: It has a constant current driver. See the read back schematic here: laser driver schematic. The wires of the driver PCB were really weakly soldered, they came off after a turning the module around a few times. The quality of these modules are questionable, but what does one expect, at a price of roughly 8 USD.

Driver PCB
Driver PCB

Since the optics were rather misplaced, I had a look at the frequency doubler crystal. It seemed slightly broken as well, so I knocked it off. Note that one should never run the diode at full power without protection glass, even invisible light can harm the eyes. Nevertheless, you can see a very weak red glow when you run it at low power. Also, you can use a standard webcam with a lens without IR filter to estimate the light intensity coming out of the diode.

The potentiometer is used to set the maximum diode current. Don’t overdrive, the diode can die instantly. It has no built-in photodiode for feedback stabilization, but  the regulator circuit seems quite robust to voltage swings. Do not exceed 5V through,  the transistor will heat up. Since I don’t have the specs of the diode, I don’t know how long it will last under continuous load.

Laser diode
Laser diode

There’s more experimenting to come, like modification of the driver circuitry in order to modulate the laser with a low frequency. Still awaiting the next batch of lasers..

For further reference, I recommend the well known LaserFAQ at:

http://www.repairfaq.org/sam/laserfaq.htm