Quote Originally Posted by GSTR View Post
Defining "output" as "what happens when you point it at a piece of wood"
HAHA! Love this analogy. But do remember that not all lasers are designed with maximum power output as their goal. Many designs actually eschew ultimate peak power in favor of other performance factors like long coherence length, lower divergence, greater pumping efficiency, and so on.

1. In a fiber laser, what effect does the length of the "gain cable" have on the output?
In general, more fiber = more gain medium = higher potential power output. I say "potential", because there could be other limiting factors (insufficient pumping energy, thermal problems, etc). Also, fiber lasers in particular are quite unique and specialized. For example, some are designed for very high power, while others are better classed as "optical repeaters" that start lasing at near unity gain and only go up a little bit from there.

2. In an Nd:YAG laser, what effect does the length and diameter of the rod have on the output?
Again, in general, more gain medium = more power. But there are trade-offs. Increase the diameter of the rod and you increase thermal issues, because heat in the middle of the rod has a harder time getting out. Increase the length of the rod and you'll almost always get better divergence, but at the price of making it more difficult to align the cavity. (This assumes external mirrors, obviously.)

3. Assuming a "PlayStation 3-compatible TOSLINK of average materials quality" fiber optic cable, and assuming you put the beam emitted by http://www.wickedlasers.com/arctic directly into the core of said cable, what would be the output?
I don't know the exact specs of the fiber used for TOSLINK cables, but based on their price I'd guess it's the cheapest multimode fiber they can find. I do know that they are designed for use with red and infrared sources (the WL Arctic output is blue at 445 nm) and they are also limited to relatively short lengths (50m?). So you are definitely going to have optical losses due to the quality of the cable (or lack thereof) and you may also experience losses because of the shorter wavelength light you're trying to couple into the fiber. You would still have some visible output at the other end, and it might still be powerful enough to burn some things, but you won't have anything resembling a "beam" at the other end. (Though you may be able to clean it up with some output optics.)

In contrast, that same WL Arctic when properly coupled into single-mode fiber could probably be transmitted several hundred meters and still come out the far end with 75% of the original power, which will absolutely still burn lots of things. If memory serves, standard single-mode fiber used in commercial remote-head laser projectors loses only 2 or 3 dB per *kilometer* of fiber. (3dB would equal a 50% power drop.) To that you need to add coupling losses of course, but it's still clear that runs of a few hundred meters are not a big problem for good quality single-mode fiber.

DZ has a projector that he can run off a 300 mw Reliant Kr/Ar laser. (The Reliant is a table-top single-phase whitelight ion unit with a big honkin' fan on top to keep the tube cool.) More importantly, he has a fiber launch for this setup that he can attach fairly quickly. We've demonstrated this at a few of the Florida meets over the years, and it's always cool to see the loops of fiber (probably 50-75 ft worth) coiled up on the table and glowing ever so slightly when he lights it up. And yet the image on the wall (projector output) looks just as good with the beam running through the fiber as it does when he removes the fiber launch and sends the raw beam straight into the projector. (Wish I could find some video of this, but I'm stumped... Maybe someone else has a clip of this stashed on their hard drive somewhere?)

Adam