ANALYSIS OF THE TEMPORAL AND SPATIAL CHARACTERISTICS OF THE OUTPUT FROM SHORT-INVERSION-TIME SELF-TERMINATING LASERS WITH VARIOUS RESONATORS

The diffraction theory of resonator modes fails to predict the output characteristics from short-inversion-time self-terminating lasers, because of insufficient time available for mode establishment. A geometrical approach based on repeated imaging of an initial spontaneous emission source in successive round trips by resonator optics is used to predict the output characteristics of such lasers. The effective size and the location of the image of the initial source, as seen from the output plane, determines the output divergence. Because of the widely different focal lengths of the two mirrors used in an unstable resonator, an asymmetry in the characteristics of the outputs from the two ends is expected. These predictions were tested in copper vapor lasers with a variety of stable, unstable, self-filtering unstable (SFUR), and diffraction-filtered (DFR) resonators. Output divergence close to the diffraction limit is obtained with SFURs and DFRs. The outputs from opposite ends of an unstable resonator show a difference in divergence of as large as a factor of three. It is shown that the proposed approach successfully explains the output characteristics.