Lasers: principles, applications and energy measurements : Laser principles

Laser principles
Lasers: principles, applications and energy measurements

Authors : Costel SUBRAN, Jean SAGAUT, Sophie LAPOINTE

Review date: March 9, 2026 | Lire en français

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1. Laser principles

The laser is an optical oscillator, and every laser therefore consists of the three basic elements of an oscillator:

an amplifying medium supplied with energy by an external source ;
a positive feedback, allowing the amplified energy to be reinjected into the amplifying medium;
and a coupling of the energy generated in the amplifying medium to the outside.

Absorption

An ordinary material, even a transparent one, always absorbs light to a greater or lesser extent. The atoms or molecules making up the material absorb the incident photons, and thus find themselves in higher-energy states (figure

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Laser principles