Optical Amplification of the Apparent Rate of Rotation of a Reflector in Q-switching a Laser Resonator

Abstract

GIANT pulses of output radiation are produced by a laser when the quality factor (or Q) of the resonant reflecting structure of the laser cavity is suddenly increased after establishing a strongly inverted population distribution in the laser material¹. The change in Q may be produced by rotating one reflector of the resonant cavity rapidly about an axis perpendicular to the emission direction, phasing the pumping of the laser medium so that the mirror comes into the position giving maximum Q just after maximum inversion has been attained (Fig. 1 A). The optimum rate of switching depends on the transit time of light in the resonant cavity of the laser, and high rotational speeds are required. A limit to the maximum rotational speed is often set by the practical difficulty of driving the mirror, and this limit may be well within the ultimate limit at which mechanical distortion and risk of failure in the mirror under the rotational forces is incurred. The maximum peak power output which may be extracted from the laser as a single pulse will be restricted : (1)i if the switching is too slow; (2) if the peak power density on the reflector may damage it; (3) if an accidental resonant structure exists, independent of the rotating reflector (and possibly with a lower Q), which may drain off some or all of the available energy before the rotating mirror comes into position.