Editorial Feature

Laser Mode Locking - Theory and Applications

Mode locking is a technique used to obtain ultrashort pulses from lasers. Lasers that are mode locked are capable of producing pulses with pulse widths in the order of sub-pico seconds, or even femtoseconds.

In mode locking, a fixed phase relationship is introduced between the longitudinal modes of the laser's resonant cavity. A laser at this state is said to be phase or mode locked.

Theory of Mode Locking

Laser light is composed of a set of frequencies; the standing waves that form a set of discrete frequencies are called longitudinal modes of a laser cavity. In a simple laser, each of these longitudinal modes will oscillate independently.

When each mode is made to oscillate at a fixed phase between each other, the laser is said to be mode locked. There are three methods of mode locking. These are, namely, active, passive, and hybrid.

Active Mode Locking

In this method, a standing wave acousto-optic modulator is placed in the laser cavity. When this modulator is driven by an electric signal, it causes amplitude modulation of the cavity, thereby causing mode locking of the laser.

Passive Mode Locking

For passive mode locking, no external signals are required; the light in the laser cavity is used to cause changes in the intra-cavity elements.

Hybrid Mode Locking

In some semiconductor lasers, a combination of the above two techniques is used for mode locking. This is called hybrid mode locking.


Some of the applications of mode locking of lasers are given below:

  • Harmonics generation
  • Medical – eye surgery
  • Optical data storage
  • Nuclear fusion

Tell Us What You Think

Do you have a review, update or anything you would like to add to this article?

Leave your feedback
Your comment type

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.