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Pulsed Lasers

Pulsed lasers are lasers which emit light not in a continuous mode, but rather in the form of optical pulses (light flashes). The term is most commonly used for Q-switched lasers, which typically emit nanosecond pulses, but this article gives an overview of a wider range of pulse-generating lasers. Depending on the pulse duration, pulse energy, pulse repetition rate and wavelength required, very different methods for pulse generation and very different types of pulsed lasers are used. The article on pulse generation describes more in detail the technical methods, whereas this article discusses some types of pulsed lasers:

• Various types of actively or passively Q-switched lasers emit pulses in the nanosecond duration regime; particularly compact microchip lasers can also generate sub-nanosecond pulses. Most Q-switched lasers are solid-state bulk lasers, and some of them can achieve high pulse energies in the millijoule or even multi-joule region.
• Some solid-state bulk lasers are pumped with flash lamps but not Q-switched; in free-running mode, one obtains longer pulses and somewhat higher pulse energies.
• Excimer lasers are used for generating intense nanosecond pulses in the ultraviolet spectral region. They are pumped with rather short electric pulses.
• Ultrashort pulses with durations in the picosecond or femtosecond domain are usually generated with mode-locked lasers, which may be solid-state bulk lasers, fiber lasers or semiconductor lasers. Their pulse energies are generally quite small, and the pulse repetition rate is usually in the megahertz or gigahertz region. For higher pulse energies (roughly an order of magnitude more), one may use a cavity-dumped laser.
• Gain-switched semiconductor lasers are suitable for nanosecond or picosecond pulses with relatively low energy.
• Relatively long pulses can be generated e.g. with laser diodes in quasi-continuous-wave operation.

For boosting the average power (particularly of high repetition rate pulse trains with moderate pulse energies), high-power fiber amplifiers are often well suited. For ultrashort pulses with much increased pulse energies, one uses regenerative amplifiers and multipass amplifiers. A laser system combined with some kind of optical amplifier is often still called a laser as a whole.

See also: pulse generation, pulses, lasers, Q-switched lasers, mode-locked lasers, ultrafast lasers, gain switching
and other articles in the category light pulses

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