Apparatus for treating materials by means of a laser beam

A device ( 1 ) for machining materials by means of a laser beam ( 2 ) comprises a lens arrangement ( 4 ) through which passes the light emitted by a laser source. Said lens arrangement ( 4 ) is tilted relative to the optical axis ( 5 ) and arranged eccentrically in order to change the cross-sectional area of the laser beam ( 2 ), particularly from an elliptical to a circular geometry, and at the same time to compensate an inclination angle of the laser beam passing through the lens arrangement in relation to the optical axis. This makes it possible to ensure the quality of the cut surface through essentially corresponding entry and exit cross-sectional areas of the laser beam ( 2 ) on the material, without the laser beam ( 2 ) having to be circularly polarized for this purpose. The costs for producing the device ( 1 ) can thereby be kept comparatively low.