Patent ID: 8687178

Claim:
A process for testing a laser device adapted to emit pulsed focused laser radiation having a focal position which is adjustable both in and across a direction of propagation of the laser radiation, the laser device including a contact element that is transparent to the laser radiation and has an abutment surface for abutment of an object to be machined, the process comprising the following steps: applying onto the abutment surface a test object that is transparent to the laser radiation at least in a machining region, the test object comprising: an interlayer that can yield a plurality of discoloration zones in response to the laser radiation; and one or more reference markings marking a specified piercing region indicating where a particular discoloration zone corresponding to a particular depth appears only if the laser device is calibrated; beaming the laser radiation into the test object bearing against the abutment surface and moving the focal position in accordance with a predetermined test pattern to generate permanent machining structures in the test object, the test pattern comprising instructions to move the focal position to a sequence of z-depths including the particular z-depth, the focal position generating the machining structures comprising the discoloration zones ascending in a stair-like manner in the direction of propagation of the laser radiation towards an outer surface of the test object facing the abutment surface; and determining a z-calibration of the laser-device by: if the particular discoloration zone corresponding to the particular depth appears at the specified piercing region, determining that the laser-device is calibrated; and if otherwise, determining a correction for correcting the z-calibration from a gradient of the stair pattern.