The present invention relates to an unstable laser resonator with output coupler having radially variable reflectivity.
The main problem with laser resonators is that they generate a high-intensity beam with minimum divergence. Present resonators for high-intensity laser beams belong to the unstable resonator category.
A known unstable laser resonator requires the employment of a totally reflecting concave mirror at one end of the resonating cavity and a small totally reflecting convex mirror at the other end. Such a resonator is characterized at the smaller mirror by a stepped reflectivity curve which causes emission of a laser beam to be null in the centre and maximum on the periphery distributed according to a circular ring with extension equal to the difference in the dimensions of the two mirrors. The output beam is thus perturbed by the diffraction effects which occur at the side edge of the smaller mirror.