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We describe a diode-pumped Yb:YAG laser that produces 1080 W of power cw with 27.5% optical optical efficiency and 532 W Q-switched with M(2)=2.2 and 17% optical-optical efficiency. The laser uses two composite Yb:YAG rods separated by a 90 degrees quartz rotator for bifocusing compensation. A microlensed diode array end pumps each rod, using a hollow lens duct for pump delivery. By changing resonator parameters we can adjust the fundamental mode size and the output beam quality. Using a flattened Gaussian intensity profile to calculate the mode-fill efficiency and clipping losses, we compare experimental data with modeled output power versus beam quality.

A new switching mechanism in a two-terminal semiconductor heterolayer structure is proposed which capitalizes on nonlinear electron temperature effects in adjacent heterolayers. The estimated switching speed of an optimized heterostructure hot electron diode should be extremely fast, perhaps as fast as 200 fs. Data are presented on prototype devices which show the expected negative differential resistance and indicate that the basic physical model is correct.