ABSTRACT
The design and technology of semiconductor lasers has come a long way since their advent in the early 1960s, and as a result, these lasers have revolutionized communications, spectroscopy, data, and material processing. Semiconductor lasers are now preferred over gas and solid-state lasers due to their wide tuning rage, high wall plug efficiency, compactness, low cost, and reliability. Unlike gas lasers there is a strong dependence of the local refractive index on the carrier density in semiconductor lasers, which affect mode discrimination and beam quality severely in a diode laser. For modern semiconductor laser designs, improved crystal quality meant reduced propagation losses and decreased thermal resistance as the lasers could now be made thinner, broader, and longer without compromising on the crystal quality. Modern semiconductor lasers use variants of the SCH design and the active regions are generally undoped. Recombination of injected carriers resulting in spontaneous emission is a major route to carrier loss in semiconductor lasers.
