Resonator mirror for an optical resonator of a laser apparatus, and laser apparatus

A laser device, comprising:

• an optically-active medium having a plurality of frequency bands;
• first and second resonator mirrors, the resonator mirrors arranged around the optically-active medium to form an unstable optical resonator, the unstable optical resonator having an optical axis;
• wherein the second resonator mirror includes a structured area, the structured area occupying less than 30% of the second resonator mirror, the structured area located on the optical axis, the structured area having at least one reflective surface that is offset against a reflective surface of the second resonator mirror outside the structured area, the offset being along the optical axis and equal to half or multiples-of-half of a selected wavelength in a desired frequency band;
• wherein the structured area introduces reflection losses for frequency bands to be suppressed, the desired frequency band thereby having higher net amplification than the suppressed frequency bands during operation of the laser device;
• and
• wherein the first resonator mirror and the structured area form a stable optical resonator near the optical axis, the stable optical resonator seeding the unstable optical resonator during operation of the laser device.