Electron beam scanlaser

Abstract

This paper reports en experimental studies of the Electron Beam Scanlaser, a scanning laser device in which the transverse position of focused laser light is controlled by means of a conventionally deflected electron beam. In the Scanlaser, the method of scanning is based on a transversely degenerate laser cavity in which the Q is spoiled for all transverse modes but one. The resonator we are using is the Flat Field Conjugate (FFC) Resonator, which is capable of supporting as many as 107nearly degenerate transverse modes, and mode selection is accomplished by means of a modified electro-optic display tube, in which an electron beam induces a localized birefringence in an electro-optic crystal. Using a 25 \times 25 \times 3 mm z-cut KDP (or deuterate.d KDP) crystal and a low resolution 10 SP-type electron gun with conventional magnetic deflection, we have observed a field of 120 × 120 fully resolved spots. The active medium is a pulsed mercury hollow cathode discharge, emitting at 6150 A; the laser power in a one-microsecond pulse is 15mw, 20db greater than the electron beam power. By operating the laser very close to threshold, it is possible to reduce the spot size of the light output with respect to the spot size of the electron beam: Similarly, at threshold, the duration of the lasing process is shorter than the time constant of the KDP, which is of the order of 30msec. In this manner, we have obtained spots as small as thirty microns in diameter, and decay times of a few millisec. Since the first operation of this device, attempts have been made to optimize both the hollow cathode discharge tube and the electro-optic mode selector, and these will be described. High speed motion pictures of the operation of the device have given considerable information on the dynamics of the charge build-up and decay, and of its influence on the laser operation.