High average-power gallium arsenide illuminators

Average optical output powers in the 5-watt range from GaAs arrays emitting peak powers of 500 watts at 10 kHz have been built for ground illumination and ranging. The thermal optical design for accomplishing this performance at 77°K is shown. The arrays described are
3\frac{1}{2}
inches in diameter and weigh 2 pounds. Overall efficiencies approaching 30 percent at 101°K and 40 percent at 77°K have been achieved. Without adjustment other than lens focus, overall tolerances of 0.1° in alignment have been shown by the use of straight, rectangular light pipes. Output beams of
2\deg \times 6\deg
have been obtained with beam uniformities of less than 10 percent.