pullbangdead said:
[quote author=Ashton link=1190257153/0#7 date=1190476430]
BUT, if you really don't care, I or someone else can just tell you.
LOL!!! Love the ending!
I'm already cramming my furry little skull full of mostly-useless computer and IT information, since that's my major, I'm not very advanced in physics yet, I tried to read the post somewhere about about how lasers work and I got a headache... I'm fairly sure my hypothesis is incorrect about lasers based on the fact that if you do the same trick with a computer CPU, it still shortens it's lifespan, even if it IS super-cooled because the circuitry just wears out faster being used more. Nothing non-biological lasts longer the more you use it. I assume you could run it at any power nearly but you would end up with a single pulse before it died.
Well, at the semiconductor/material level, to fully understand the inner workings, it's more complicated than what can be described here. The applied voltage, to put it simply, provides a bias/energy to raise the electrons to a higher energy level in the system. In a laser, this actually changes the energy bands of the materials (there are multiple layers with different materials in the diode, it's usually a double heterostructure, so there are 3 layers), allowing the electrons to move from one material to another. This voltage just supplies the energy needed to make this happen by lowering potential barriers, so extra voltage is of no good typically, so all extra voltage will do is break things. (Although, a lower temperature will also change these potential barriers in the material, so more or less voltage may be needed, but I'd have to actually stop and think about that for a minute). Once the electrons are in the active layer, there exists a "population inversion" in the active layer. This basically means that under these conditions, there is always a hole in the valence band for an electron in the conduction band to fall back into. The electrons will spontaneously fall, and emit a photon of light corresponding to the band gap (kind of like an LED). However, there will be a time before the electrons fall. This is where lasing comes in: photons previously emitted with the same energy/wavelength pass by, and Stimulate an electron to fall and emit a photon. This new photon will be coherent with the photon that stimulated its emission. Thus, the optics that make the photons bounce back and fourth before being emitted, resulting in amplification of the light (a laser without the optics is simply a light amplifier). A new electron will replace the fallen electron in the conduction band of the active layer, and the process repeats.
As far as current itself, more electrons in the active layer means more electrons to fall through the potential barrier, means more electrons stimulated by photons, which means more photons, so power increases VERY rapidly with current. But, from what I've read, the main mode of failure for an LD is the "COD" that others have mentioned elsewhere. This is a function of too much power damaging the optics and mirrors that are required for lasing to occur. So, unless cooling makes the optics less susceptible to damage, I don't think it will help at all. The light amplification and emission might become more efficient, but without the optics you can't get the stimulated emission that makes it all work.
I could go into greater detail, but that would require more semiconductor and device theory than you probably know. [/quote]
You hit it right on the nose!
Nice to see a fellow engineer on board...
Good to see you paid attention in your Semiconductors class
(I had to as well... my professor was, let just say, difficult :
)
--DDL
