Output Characteristics of the Laser

Abstract

The characteristics of the laser are determined by the interaction between the light and the atoms in the resonator under the influence of pumping and relaxation. There are different theories of the laser in treating these factors. They are classified into the rate-equation theory, the semiclassical theory, and the quantum-mechanical theory. In the quantum-mechanical theory, both light and atoms are treated quantum-mechanically, while in the semiclassical theory the light field is treated as classical electromagnetic waves according to Maxwell’s equations, and the atoms are treated quantum-mechanically. The rate equations describe temporal changes of atomic populations and light energy or the number of photons, neglecting the phase of the light and the atomic polarization. Therefore, the rate equations cannot be applied to subjects such as the frequency of the laser or the characteristics of multimode oscillation.