LASERS - just a bit about them
June 14, 2011
Just a couple ideas for those who are set on experimenting with lasers.
FIRST and most important: Lasers are dangerous. I am not espousing that you do anything with lasers, as you can be blinded BEFORE YOU CAN BLINK, if you use lasers stronger than the common "keychain" laser pointers.
SECOND: If you DO work with lasers the next IMPORTANT thing is to get yourself laser glasses or goggles. The OD rating is the optical density, which means how well these glasses will protect you from eye damage. OD of 2 means laser light is cut to 1/100th its prior level. If you use OD2 glasses with a 1 watt laser, 1/100th of a watt or 10 milliwatts still gets through and that is dangerous to the eyes. OD3 means laser light is cut to 1/1000th the original. For lasers in the watt range, OD3 is the least protection you should accept.
THIRD: Do NOT use common sunglasses or glasses or goggles that say they are for lasers, but do not show their OD rating at the frequency of your laser. Ask yourself this, "How much is my eyesight worth to me?"
FOURTH: Lastly, if you do screw up, don't say I didn't warn you how dangerous lasers are.
Now what I was thinking of posting here are a couple schematics to give you an idea how to build a laser pulser circuit. These can also be used for pulsing LEDs as well, especially the high current/high brightness LEDs. These circuits are only guides and need to be adjusted to work within the parameters of the LEDs or LASERs you are working with.
LED high-brightness pulser circuit
This transistor drew about 22.5 mA from the picaxe output, and sent 250 mA through the diode. This varies slightly with each individual transistor. NOTE that the picaxe outputs are not supposed to go over 20 mA each, and I was drawing a little more than that. Consequently, remember that you MUST let the circuits cool down after each pulse. I indicated not repeating the pulses more often than 1000 times per second (1 kHz.)
I tested this with the components shown and was getting ~250 mAmp pulses through the LED as indicated. Repeated at 1kHz. you should definately see brighter light from the LEDs. And, YES, this can shorten the life of your LEDs. I am only showing how it might be done, not advising you to do it. <g>
In the above circuit, I used 2N2222s in a darlington configuration. I have some actual darlingtons here, but did not use them because they did not respond quickly enough for proper pulse shaping. The 2N2222s are borderline and results can vary from transistor to transistor, (so I would advise using an oscilloscope when building your driver circuit). Higher frequency transistors should work better, but I chose 2N2222s because they are common. You might also use 3 or 4 series LEDs in the circuit to test it before trying it with a more expensive Laser diode. This latter circuit draws much less current from the picaxe chip than the earlier one.
Good Luck and **Be Careful**.
@ Tinhead - You mentioned your laser diode is in the 50 to 200 mW range. The laser diode I used here is a bit stronger, but I limited the current to be in the same ballpark. At 3.7 volts it passes 200 mA, with an average power out of 53 mW.
The minimum voltage is supposed to be 3.8 volts, but this one still lased at 3.7 volts. Take a look at the pictures and ask yourself if your laser will do the same. If not, you might try pulsing it.
Not exactly wood, this is only paper, but how quickly it starts to burn shows that it would go through wood as well, just slower.
...and you also mentioned plastic. Here I took an old junk CD (One of those we used to get in the mail free from AOL and other places.) And because dark colors will absorb heat quicker, I tried this on the shiny side of the CD -- being careful about where the laser beam would bounce to if it did reflect ! --. Each letter took between 5 and 10 seconds to burn in. As above this was 3.7 volts supply giving an average 53 mW PULSED output, not CW.