TABLE OF CONTENTS In this Chapter, we reviewed the fundamental physical concepts relevant to lasers, including stimulated emission, resonant cavity, waveguide, propagation of an electromagnetic wave in a waveguide and the laser beam divergence, and waveguide design. We introduced the notion of absorption, spontaneous and stimulated emission, the Einstein coefficients, resonant cavity, population inversion and threshold. The example of the ruby laser was used to illustrate these concepts.
The discussion was then focused on semiconductor lasers, which are becoming dominant for numerous modern applications. The concepts of gain, threshold current density, transparency current density, linewidth, external differential quantum efficiency, mirror loss and internal loss were introduced. The different types of semiconductor lasers were then described, including homojunction, single and double heterojunction, and separate confinement and quantum well lasers. The fabrication and packaging technology of semiconductor lasers were then briefly described. Finally, a few specific examples of lasers were presented, including quantum cascade, type II, vertical cavity surface emitting lasers, low-dimensional lasers, and Raman lasers.
