Laser Beam Steering.

An electronic beam scanner for CO2 lasers was designed and constructed. Specific requirements to be met were three degree scan range, 100 resolvable beam positions, 6000 Hz raster scan in one dimension, and a capability for 100 W of 10.6 micrometer output. The device employs acousto-optic Bragg diffraction using germanium with a longitudinal acoustic wave and laser beam polarization in the crystallographic 111 direction. Sawtooth FM over a 27 MHz band centered near 100 MHz is used to provide the scan mechanism. A single small Ba2NaNB5O15 transducer provides sufficient acoustic beam divergence to yield a 3 deg. scan capability with a 1.4 dB falloff in output beam power at the scan limits. Direct-contact water cooling of the Ge crystal is provided to prevent thermal runaway. Cylindrical, reflective, telescopic optics are used for beam conditioning and recollimation. Computer calculations provided impedance characteristics and frequency response curves for general transducer design. Transducer bonding was done ultrasonically using thin metal films of Ag, Au, and Ag-In. The AG-In gave best overall performance. An rf-to-acoustic conversion efficiency of 34 was achieved at band center 4.7 dB effective transduction loss. Radio frequency driver power required for 50 70 diffraction efficiency was 31 49 W.