Optical pulses with pulse durations in the nanosecond regime are required for many applications, including laser material processing, distance measurements, and remote sensing. In most cases, they are generated with lasers, either by Q switching or by gain switching.
Q-switched lasers can deliver high pulse energies – for example, several millijoules from solid-state lasers with moderate sizes, and multiple joules from somewhat larger devices. Depending on design details, the emission may occur in a single longitudinal mode of the laser resonator, in this case leading to a very narrow linewidth.
Gain-switched lasers can also generate nanosecond pulses, but with much lower pulse energies. In the case of semiconductor lasers, the peak power is often limited to the order of 1 W. Gain-switched fiber-coupled semiconductor lasers are interesting seed sources for fiber amplifiers, and such MOPA devices are increasingly seen as a possible substitute for Q-switched lasers in many cases, at least for pulse energies not exceeding a few millijoules. One of the main advantages is the great flexibility of modifying both pulse repetition rate and pulse duration electronically, and keeping the pulse duration constant when the repetition rate is varied in large ranges. Also, such devices can be fabricated at lower cost.
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See also: lasers, pulse generation, Q switching, Q-switched lasers, gain switching, pulse duration, picosecond lasers, femtosecond lasers
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