Optical resonator for a laser beam, having the following characteristics: • the optical resonator comprises at least 4 mirrors (M1-M6), • the mirrors (M1-M6) form a ring resonator, • Each beam path (L1-L6) connects two consecutive mirrors (M1-M6) to each other, • the mirrors (M1-M6) are arranged in at least two different planes, • to generate image rotation during operation, which is a rotation of the cross-sectional beam image of the laser beam, such • that the mirrors (M1-M6) are spatially arranged, • that the image rotation angle per resonator revolution is such, • that at least five resonator revolutions are necessary, until the original beam image orientation is substantially restored, where a substantially restored beam image orientation means the original beam image orientation ±4°, if up to 100 revolutions are required to repeat the image, respectively the original beam image orientation ±1°, if more than 100 revolutions are required to repeat the image. Wherein, • that the optical resonator comprises exactly six mirrors (M1-M6) and six beam paths (L1-L6), such that, • a first beam path connects a first mirror with a second mirror, a second beam path connects the second mirrors with a third mirror, a third beam path connects the third mirror with a fourth mirror, a fourth beam path connects the fourth mirror with a fifth mirror, a fifth beam path connects a fifth mirror with a sixth mirror and the sixth beam path connects the sixth mirror with the first mirror, • the first beam path is arranged parallel to the fourth beam path and both parallel beam paths (L1, L4) form a basic plane, • the third mirror and the sixth mirror, i.e. the two mirrors which are not arranged at the ends of the first beam path and the fourth beam path, are each arranged outside the basic plane. • the optical resonator comprises at least 4 mirrors (M1-M6), • the mirrors (M1-M6) form a ring resonator, • Each beam path (L1-L6) connects two consecutive mirrors (M1-M6) to each other, • the mirrors (M1-M6) are arranged in at least two different planes, • to generate image rotation during operation, which is a rotation of the cross-sectional beam image of the laser beam, such • to generate image rotation during operation, which is a rotation of the cross-sectional beam image of the laser beam, such • that the mirrors (M1-M6) are spatially arranged, • that the image rotation angle per resonator revolution is such, • that at least five resonator revolutions are necessary, until the original beam image orientation is substantially restored, where a substantially restored beam image orientation means the original beam image orientation ±4°, if up to 100 revolutions are required to repeat the image, respectively the original beam image orientation ±1°, if more than 100 revolutions are required to repeat the image. • that the optical resonator comprises exactly six mirrors (M1-M6) and six beam paths (L1-L6), such that, • a first beam path connects a first mirror with a second mirror, a second beam path connects the second mirrors with a third mirror, a third beam path connects the third mirror with a fourth mirror, a fourth beam path connects the fourth mirror with a fifth mirror, a fifth beam path connects a fifth mirror with a sixth mirror and the sixth beam path connects the sixth mirror with the first mirror, • the first beam path is arranged parallel to the fourth beam path and both parallel beam paths (L1, L4) form a basic plane, • the third mirror and the sixth mirror, i.e. the two mirrors which are not arranged at the ends of the first beam path and the fourth beam path, are each arranged outside the basic plane.