Laser diodes are the most basic part of the laser. They determine the color, power, and divergence. Their power is measured in mw, which stands for milliwatts, they come in several common wavelengths, as well as a few exotic ones too.
There are 3 main shapes of diode:
and I forget the other one (VECSEL?)<--maybe lol i dont know i think it was flat
As well as 3 common sizes:
There are several manufacturers of laser diodes.
Some diodes are more efficient than others meaning that they put out more light relative to the input power.