ABSTRACT
Laser physics includes such basic phases as population inversion, energy levels, and stimulated emission. Lasers which use a solid-state media are generally operated in a pulsed mode. The most common solids used are ruby crystals and neodymiumdoped glass and neodymium-doped crystals such as Yttrium Aluminum Garnet (YAG). The pulse envelope from a long pulse or so-called "normal mode" solid-state laser will appear, when viewed photoelectrically, as a series of random "spikes". The laser "standing waves" are produced when an integral number of half-wavelengths exactly fit into the separation hetween the mirrors of the Fabry-Perot cavity. The concept of controlling Q-Switched laser outputs with a time-variable reflectivity (TVR) was first introduced by Vuylsteke in 1963, with his pulse-transmission-mode (PTM) Q-Switched laser. Mode locking is usually accomplished by inserting an ultrafast intensity dependent "switch", such as a bleachable dye, inside the resonant laser cavity. Laser research and development have been supported essentially by the military and by industry.
