  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
continuous-wave Nd:YAG oscillator, and subsequent amplification, allowed the
generation of rectangular pulses with pulse lengths on the order of the Nd:YAG
fluorescence lifetime. Temporally flat-top pulses of 1064 nm light with 520 mJ
pulse 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 spatially flat-top
beam at 1064 nm used in the amplifier is converted to a Gaussian beam at 532 nm
with beam quality factor $M^2=1.41(14)$ during the second harmonic generation.
This system has potential as a pump source for Ti:sapphire, dye, or optical
parametric amplifiers to generate tunable high-power single-frequency radiation
for applications in precision measurements and laser slowing.
