808nm - $600

Good question.
I was under the impression that you ALWAYS have some divergence >0 on a laser beam.
Or am I missing something here.
http://en.wikipedia.org/wiki/Collimated_light
In reality, there is no such thing as something being perfectly parallel.

There probably always is some divergence - I'm sure you're right about that.

However, I'm doubtful that this is dictated by laws of "physics" as opposed to simply our practical manufacturing abilities, and actual physical tolerance requirements.

Without calling Albert Einstein into this, I'm pretty sure there is no such thing as
100% perfectly parallel light (or parallel anything for that matter) anywhere in nature.
Even the light that reaches the Earth from distant stars is not perfectly parallel, even though
we can assume it is for all practical purpose.

If you want a hard physical explanation, I don't know it right away, would have to do some digging.
Where's cyparagon when you need him?

I guess you could make it a philosophical issue as well if you like.

I understand your point - but Cm 96 doesn't occur anywhere in the universe naturally. It's still an element on the periodic table that we can create with enough motivation

It probably is a largely philosophical question. I agree. Mostly because I can't envision anything in the physics of it that would deny perfectly parallel light. Complete vacuum, nothing to distort it, etc. Those may be conditions that don't occur naturally, but that's just a practical limitation, not a physics-based one. Or at least that would be the side of the coin I would put my money on, until someone like cyparagon comes and tells us why we're both wrong

Perfect parallel light requires an infinite large beam. A limited beam side means divergence because of the wave nature of light.
In the quantummechanical picture the photons have a uncertainty in their position, so a perfect parallel beam is probably not possible by the Heisenberg uncertainty principle. I haven't looked it up, but this would be my guess.

Also, any light that has a wavelength that is not infinetly small (impossible by the way), will not be perfectly parrallel as the very word wavelength implies the light is moving in waves not in straight lines.
So for an ir diode the light would complete a whole wave every 808nm; during this wave the light would cease being able to be perfectly parrellel as it is moving in waves.
Sory if my wording is not very clear, I need some sleep

sorry for this little OT, but these 808nm modules laser module seem like those from O-like but I've never seen a 4W one :thinking: