Regenerative Ruby Laser Amplifiers

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Abstract
An ideal laser amplifier was previously treated as a three-medium transmission system. It was predicted that for a given length, the gain would rise with negative attenuation (population inversion), reach a maximum, decrease rapidly at first, and then gradually approach zero asymptotically.The theory has been tested experimentally, using ruby at liquid-nitrogen temperatures. By controlling the relative times of firing of two rods, one acting as oscillator the other as amplifier, the transmitted power gain was studied. When both the oscillator and amplifier rubies were uncoated, they could be made to oscillate for about 100 µsec giving a well-defined pulse of quasi-cw operation. The gain of the amplifier increased when the input signal from the oscillator approached the time at which the amplifier went into oscillation. If the oscillator was delayed so that its signal occurred at increasing time after the amplifier oscillations had ceased the power gain decreased, even though the amplifier crystal was still being pumped. Finally, with still further delay of signal relative to the amplifier oscillation period, attentuation in transmission was observed.