Pulse stretching and shape control by compound feedback in a Q-switched ruby laser

Abstract

Feedback control is employed to stabilize the output of a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> -switched ruby laser. A computational model of the rate equations plus feedback terms is used to examine pulse shapes with changing feedback parameters. It is shown that a lengthened flat-top pulse cannot be obtained with negative feedback alone, a compound feedback arrangement is suggested to facilitate this. A practical laser system is constructed with an associated feedback loop, good agreement is found between theory and experiment. Pulses flat to within ±5 percent are obtained with durations up to 600 ns and are amplified with no apparent saturation. Output powers of 15 MW are achieved for hundreds of nanoseconds with a divergence of 7 mrad and a spectrum consisting of transform-limited lines separated by the axial mode spacing.