Process of formation of ultrashort pulses in a YAG:Nd laser

An investigation was made of the formation of a train of ultrashort pulses in an yttrium aluminum garnet laser. This process was found to depend strongly on the ratio of the radiation intensities in the active material and in a nonlinear absorber. A suitable selection of this ratio increased the efficiency of selection of the fluctuation pulses with the highest amplitude and this improved considerably the contrast, i.e., the ratio of the intensity of the principal pulses to the.intensity of the background. A criterion of the correct selection of the conditions was the presence of two definite thresholds, one of which corresponded to free oscillations and the other to the appearance of a train of ultrashort pulses. The ease of selection of the optimal conditions increased with the width of the free-oscillation region. The present investigation provided means for increasing the reproducibility of the output from one flash to another and for improving the contrast of the output radiation. The investigated laser could be used as a master oscillator in high-power neodymium-glass laser units intended for plasma heating.