ABSTRACT
Laser resonator is a crucial component of lasers. It provides a feedback necessary for the continuous wave operation of a laser and controls optical beam quality and laser spectrum. This chapter briefly discusses basic equations and focuses on a description of modern computing methodologies allowing one to get detailed information about the modal properties of loaded resonators including compound systems. Laser resonator classification with an emphasis on specific resonators is developed in connection with the appearance of new configurations of the gain media. The chapter discusses nonlinear effects associated with nonuniform gain saturation and refractive index variations induced by laser intensity. The primary purpose of the laser resonator theory is to describe the so-called transverse (or spatial) optical modes in a bare resonator free of a gain medium. Many practical laser resonators consist essentially of two end mirrors with the gain medium in the middle.
