  A compact frequency-doubled diode-pumped Nd:YAG master-oscillator
power-amplifier laser system with programmable microsecond pulse length has
been developed. Analog pulse shaping of the output from a single-frequency cw
Nd:YAG oscillator, and subsequent amplification, allowed the generation of
rectangular pulses with pulse lengths on the order of the Nd:YAG fluorescence
lifetime. Rectangular pulses of 1064 nm light with 520 mJ energy, 2.6 kW peak
power, and 200 $\mu$s duration, with linewidth below 10 kHz, were obtained at a
repetition rate of 2 Hz. Second harmonic generation in a LBO crystal yielded
pulses of 262 mJ and 1.3 kW peak power at 532 nm. The peak power can be
maintained within 2.9% over the duration of the laser pulse, and long-term
intensity stability of 1.1% was observed. The 532 nm beam is roughly Gaussian,
with $M^2=1.41$ during the second harmonic generation. This system has
potential as a pump source for titanium:sapphire, dye, or optical parametric
amplifiers to generate tunable high-power single-frequency radiation.
