Kenom said:
Now this is where I'll have to put in my $.02. Since Green lasers utilize more than one optic they are capable of getting the divergence down quite a bit. With all of the reds we are playing with the lenses are pretty basic and are just focusing lenses, not colimating lenses. Now this is my understanding. I however do NOT really understand optics all that well so I am probably wrong!
Sorry Ken, I'm gunna have to kick you in the teeth here
(all in good fun of course!)
There is a theoretical perfect beam, a beam where your M^2 is 1.0. The larger your M^2, the further it is from perfect. For a green laser, M^2 of 1.0 would roughly correlate to 0.68mm*mRad - where mRad is your full-angle divergence, and mm is your spot diameter at the smallest point on the beam. Now, the proportions can be changed up. You could have a 0.68mm beam and 1.0mRad, a 0.68mRad and 1.0mm, 68mm and 0.01mRad, etc.
Now, the more coherent a source, the closer you get to an M^2 of 1. DPSS lasers are very good, usually spec'd to M^2 of <1.2, meaning <0.82mm*mRad for 532nm. Single-mode red diodes like Greg's aren't quite as good, but they're still pretty low. The reason why you always see me complaining about multi-mode diodes though? Their M^2 spec is usually in the <20 range. Basically, your beam specs will be a good 15x worse than that of a greenie - not too attractive at all.
With the AixiZ units, pulsars, etc. they all use the same lens. The lens has a somewhat long focus that distributes the mm/mRad proportion a bit differently than we're used to with a greenie. The initial diameter is often a good 3-5mm. However, as opposed to a multi-mode red which would have 3-5mRads to match, the reds have a low divergence - in the <0.5mRad range. Take a pulsar next to a CNI greenie and the CNIs beam will be MUCH smaller in the first few feet. Go out 100meters though, and the pulsar's diameter will be a small fraction of the CNI. So neither unit has really bad beam specs, but they're in different proportions.
Cavity optics can be crucial in getting good coherence, but no matter how many external optics you shove in a greenie they could only serve one function: decreasing coherence ever so slightly and actually making the beam worse. All the optics in a greenie do help is getting a good proportion of mm to mRad for us, but they don't actually improve the (minimum diameter)*mRad factor at all.
Damn physics is always getting in the way of our fun.
