PERFORMANCE-MODEL FOR OPTICAL EXTRACTION FROM A Q-SWITCHED CHEMICAL OXYGEN IODINE LASER

A comprehensive time-dependent model for optical extraction from a Q-switched supersonic oxygen-iodine laser is described. Gas flow is treated by using an unsteady, premixed, quasi-one-dimensional model that accounts for gas motion and expansion as well as heat release in the cavity. The model uses a simplified, temperature-dependent, chemical kinetics package that consists of several reactions among the 3SIGMA, 1DELTA, and 1SIGMA states of oxygen, atomic and molecular iodine, water, and helium. Hyperfine relaxation effects on the gain and optical extraction from the 3 --> 4 line are treated by using a simple four-level laser model. An efficient algorithm for solving the coupled medium and optical extraction equations is described. This gain model, in conjunction with a geometric model of an unstable confocal resonator, is used to examine optical extraction from the medium as a function of pulse repetition rate, duty cycle, and optical mode width. It is shown that the output power may exhibit flow-induced relaxation oscillations, and the conditions under which these oscillations occur are discussed.