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Loaded gain of a flowing chemical oxygen-iodine laser is described by a rate equation. The upper laser levels are pumped by the oxygen. The laser also includes energy pooling and water deactivation. The pumping produces a hyperfine relaxation of iodine atomic sublevels and a velocity cross-relaxation of iodine atoms. Stimulation of the multimode field provides a solution to the rate equation model.

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 3-sigma, 1-delta, and 1-sigma states of oxygen, atomic and molecular iodine, water, and helium. Hyperfine relaxation effects on the gain and optical extraction from the 3 arrow to the right 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.