2. Laser beam properties

2.1 Directivity

The cavity is narrow and elongated, and only photons propagating exactly along the cavity axis benefit from amplification greater than losses: the laser beam is therefore totally directional. In fact, its divergence is very often close to the limit imposed by diffraction.

A laser beam can :

• propagate over long distances while remaining collimated;

• be focused at a point whose dimensions are limited by diffraction.