In section 4.3 the Transverse optical modes of the laser were described.

In section 4.4 the shape of the laser beam inside the cavity was described.

Figure 8.1 describes the basic transverse mode for some common optical cavities.

For each optical cavity the shape of the beam profile is marked (in dash line), and the borders (at e^-2 of the intensity) of the volume occupied by this specific mode.

In a stable resonator, with circular mirrors, the beam waist or the beam size at the mirrors surface is determined by:

• The radius of curvature of the mirrors.
• The distance between the mirrors.
• The laser wavelength.