Semiconductor lasers

Illuminate a piece of white paper, in the dark. Lasers will show speckles. And lasers usually have very low beam divergence.

Most diode lasers can be driven like an LED, constant-current, or a voltage and a current-limiting resistor.

Yep.

The OP could have just opened up a cheapie laser pointer. That would have showed him that they can be driven with three 1.5V button cells, which have such low current capability that they can't overdrive the laser.

Slightly less cheap pointers use current-limiting circuitry and can be driven by two AA cells.

Another point- some mice use IR (as in it's hard to tell when they're lasing) lasers.

Mark L. Fergerson

Hmm, no notable speckles when compared with a known LED.. Guess I'll have to go out and actually buy a laser pointer after all.

Well, I got terribly lazy. :) It was Saturday afternoon, after all, and I was in no mood to get out of the house and go shopping - since I don't have a laser pointer around.

A barefoot diode laser has a lot of beam divergence, but it's generally quite asymmetric. The NA is often about 0.15 in the narrow direction (along the laser stripe) and 0.4-0.5 in the long direction (across the stripe).

That and speckle are the best simple tests. (Oh, and blowing up if you look at them crossways, of course.)

Cheers

Phil Hobbs

Buying a laser pointer is a good start, but it's more fun to replace the pointer laser pointer head with the laser from an old 16x or faster DVD burner: Then, you can do some real damage. It's not quite a death ray, but should scale nicely with additional diodes and better optics.

Consider buying some 650nm eye protection before you proceed:

Digi-Key has 400+ items in their list, just look for "laser". The cheapest was under $6 in single quantity, although that was IR. Looks like the cheapest visible one is about $12 at 650 nm, 5 mW. Probably eBay has them even cheaper.

Jon

Another way of getting cheap (infra-red) laser diodes is to buy used SFP optical fibre transceivers on eBay. These can often be bought for around $1 and have good quality drive circuits built in. If you want to modulate them, nost of the work is already done for you. The beam diverges by around 60 degrees in total but is axially symmetric as they use vertical cavity lasers. Most digital cameras can easily see the 850nm versions, but not the longer wavelenght ones.

John

why is a test for coherence unsuatable?

Wasn't aware it existed.

Also, excuse me for being away from Usenet for a few weeks. :)

Interesting.

Is it possible that ord>>

The Dollar store used to have them for, hey $1. I still have 4 or 5 in one of my drawers.

Mikek

DX usually has a bunch of laser pointers cheap. A couple of years ago I bought a really nice red/green pointer for about $5, delivered from China (match that, Amazon! ;-).

I bought some like these a while ago, ~$2 for 10pcs delivered to UK! Could not resist even though I had no use for them.

They can put a nice little spot on the wall and have glass lenses. Inside there was a naked laser diode chip mounted directly on the edge of a circuit board with some kind of wire bonding.