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Modes of Laser Operation

Author: the photonics expert Dr. Rüdiger Paschotta

Definition: a mode of operation such as continuous-wave operation, Q-switched or mode-locked operation

Category: article belongs to category laser devices and laser physics laser devices and laser physics

DOI: 10.61835/ny9 Cite the article: BibTex plain text HTML Link to this page LinkedIn

Lasers can be used in distinct modes of operation, the most important of which are:

Continuous-wave operation (cw operation): the laser is continuously pumped and emits light continuously, either on a single resonator mode (→ single-frequency operation) or on multiple modes (see also: single-mode operation).
Quasi-continuous-wave operation (quasi-cw operation): the pump source is switched on only for short time intervals to prevent excessive heating.
Gain-switched operation: gain switching means that the pump source is turned out only for very short time intervals (below the upper-state lifetime) in order to obtain short light pulses.
Q-switched operation: the intracavity losses are modulated, so that the laser emits energetic pulses. Pumping may be continuous or pulsed.
Mode-locked operation: initiated and stabilized by an optical modulator or a saturable absorber, one or several ultrashort pulses are circulating in the laser resonator, so that a regular train of pulses is generated. Mode-locked lasers are usually continuously pumped, but mode locking with quasi-continuous pumps is also possible.
Q-switched mode-locked operation: simultaneous mode locking and Q switching occurs.

In more exotic cases, lasers exhibit chaotic oscillations or fluctuations, or exhibit only amplified spontaneous emission.

Note that with modes in this article we do not mean modes of laser resonators, but simply different regimes which can be distinguished in laser operation.

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