5C5 - An internally scanned laser

A method for producing a scanned beam of light from a laser has been devised and tested in our laboratories, and appears to be applicable to a high deflection rate scanner. Scanning is accomplished through the use of a pulsed optical delay line located within a special, enlarged laser cavity. Narrow shear pulses, traveling through the delay line, convert some of the incident, plane polarized laser light to the orthogonal polarization by means of the photoelastic effect. The converted light is diffracted and is removed from the cavity by spatial filtering at a cavity focus. The light removed in this manner is imaged onto a screen. Since the delay line is inside the cavity, light passing around the shear pulse is recirculated and not wasted. Since quartz has a shear wave propagation velocity of 3840 m/s, a delay line resonant at 30 Mc/s can propagate pulses about 0.13 mm wide. A beam 100 mm in diameter would have 770 spot locations. The system has been operated with a delay line resonant at 10 Mc/s in a 1.5 cm collimated laser beam. A resolution of 15 spot positions was obtained with a beam power of 4 mW. For TV projection applications, scanning in the orthogonal direction and modulation would be accomplished with external devices.