Optical assembly for reducing a spectral bandwidth of an output beam of a laser

An optical assembly, comprising:

• a beam-expanding optical unit within a laser resonator, the beam-expanding optical unit configured to increase a beam cross section and reduce a divergence of a resonator-internal laser beam in an expansion cross-sectional dimension so that a resonator-internal expansion laser beam section arises;
• an optical grating in a retroreflective arrangement for the resonator-internal laser beam;
• a first beam-limiting stop in a beam path of the expansion laser beam section, the first beam-limiting stop configured to act in the expansion cross-sectional dimension;
• and
• a second beam-limiting stop in a beam path of the resonator-internal laser beam on a side of the beam-expanding optical unit facing away from the grating,
• wherein:
• a width of the second beam-limiting stop is such that the first beam-limiting stop is overexposed by the resonator-internal laser beam and such that a width of a used beam cross section on the grating is defined by the first beam-limiting stop;
• and
• an adjustment range of the beam-expanding optical unit and a width of an input aperture of the second beam-limiting stop are matched to one another so that the first beam-limiting stop is fully illuminated in a case of an expansion and the first beam-limiting stop is overexposed with an increasing expansion.