Master oscillator power amplifier (MOPA) apparatus includes two seed-pulse sources coupled to a single fiber amplifier including one or more stages of amplification. One of the seed-pulse sources is a single-mode source generating pulses having a duration selectively variable between about 0.1 ns and 10 ns. The other seed-pulse source is a multi-mode source generating pulses having a duration selectively variable between about 1 ns and 10 μs. Selectively operating one or the other of the seed-pulse sources provides that the apparatus can deliver pulses selectively variable in a range between about 0.1 ns and 10 μs.