How to Determine if You Have a Diode Laser Module
So you found a bag of cute little brass devices marked 'barcode lasers' at a garage sale. They have wires coming out of one end and a lens at the other. Are they bare laser diodes or do they have a built in driver circuit? Size alone is no real indication as the driver circuits can be quite tiny. •If there is any sort of model number, try to check that out first since as we have seen, laser diodes are not very forgiving of even minor abuse.
•If you really have a *bag* of the thingies, the surest way to know what is inside is to sacrifice one and reverse engineer it - unless, of course, they are totally potted in Epoxy or something even more impervious to 20th century technology. Perhaps your friendly dentist would be willing to X-ray one for you (with or without root canal). :)
Assuming that analyzing the circuit isn't possible or appealing and they are not clearly labeled (in which case you wouldn't be reading this anyhow), closely examine the wire leads: •If there are three solid gold plated wires and they connect directly to the bottom of what looks like a metal can transistor, you have a bare laser diode. This sort of diode laser module without driver circuitry is common in equipment like laser printers and barcode scanners. Some laser diodes only have two wires but not the kind you are likely to run across in a grab bag unless one broke off. :-) If you cannot tell where they go, also assume you have a bare laser diode. See the chapter: Laser Diode Power Supplies to determine their electrical characteristics and power requirements
•If there are only two wires, probably stranded and color coded red and black, there is almost certainly an internal driver circuit. Red will be positive. A typical power requirement is 3 to 12 VDC at 100 mA. Start low while monitoring output (using an IR detector if it may be an IR laser diode). Most diode laser modules operate at a fixed maximum output power which will be where the intensity stops increasing as you raise input voltage. You can probably assume the circuit will handle, say, 25 percent more input voltage beyond this point but there is no way to how much more without reverse engineering or testing the unit to destruction. The power curve will also probably be quite non-linear - starting out as an LED until the threshold current is reached and then increasing rapidly.
CAUTION: Some diode laser modules are current controlled using optical feedback but expect a regulated DC power supply input. With these, the output will continue to increase more or less linearly as the input is cranked up until the point at which the smoke comes out. :-(
•If there are three (or more) stranded color coded wires, the additional ones may be for on-off control, modulation, or a shield or ground. Have fun determining exactly what they do (but be prepared for frustration).
