modes of laser operation (original) (raw)

Author: the photonics expert (RP)

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

laser physics

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

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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 on only for very short time intervals (often below the upper-state lifetime) 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.

Frequently Asked Questions

What is continuous-wave (cw) laser operation?

In continuous-wave (cw) operation, a laser is continuously pumped and emits a continuous beam of light. This output can be on a single resonator mode (single-frequency operation) or on multiple modes.

What is a Q-switched laser?

A Q-switched laser is one where the losses within the laser cavity are actively modulated. This technique allows the laser to store energy and then release it in the form of short, high-energy light pulses.

What is a mode-locked laser?

What is the difference between gain switching and Q-switching?

Gain switching involves pulsing the pump source for short time intervals to generate light pulses. In contrast, Q-switching involves modulating the internal losses of the laser resonator, while the pump source may operate continuously.

What is quasi-continuous-wave operation?

Quasi-continuous-wave (quasi-cw) operation is a mode where the laser's pump source is switched on only for limited time intervals. This method is often used to manage thermal effects and prevent excessive heating in the gain medium.

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