Why do diodes need lenses?

[Soren]

Diode lasers and gas lasers work on the same principles, so why do diodes need lenses and gas lasers do not? Is it because the cavity is so short?

 

[Cyparagon]

It's because the cavity is so thin.

We know that beam size is inversely proportional to divergence, so Imagine if you took a laser beam, and compressed the beam down to a few microns. The divergence would be pretty terrible. That's what a bare laser diode is.

As for the lens: the emitter is so small that you could consider it a point. You've probably seen this diagram:

Well, it works in reverse, too. Place the laser diode at the focal point of the lens, and bingo - proper laser beam.

 

[NoMercyFate]

Simple physics You've got diverging lines and you want them to form a beam with aprallel lines so thats what the lens does, else its not much of a laser

Grtz

 

[daawood123]

wait, about that reverse thing, does that mean if you screw a lens into a aixiz module in reverse, there will be a point where you will acheive fixed focus? i have tried so many time to get fixed focus with my LPC-826, but either the dot will be too large closer to the aperture or too big say 20ft away

 

[lasergal]

Diode lasers and gas lasers work on the same principles, so why do diodes need lenses and gas lasers do not? Is it because the cavity is so short?

For years I've wondered the same thing. Then I aked basically the same question here: http://laserpointerforums.com/f54/why-diode-lasers-different-73704.html

Well, that was asking about coherence lengths, but it still was pretty much the same question.