Optical apparatus, method for setting a target deformation, and lithography system

An optical apparatus, comprising:

• a mirror, comprising:
• a substrate element;
• an optical surface supported by the substrate element;
• and
• a strain gauge device;
• an actuator configured to deform the optical surface;
• and
• a closed-loop control device,
• wherein:
• the strain gauge device comprises:
• i) a path length device configured to generate a measurement spectrum of a measurement radiation;
• and ii) a waveguide configured to guide the measurement radiation to the path length device;
• the path length device comprises a grating device configured to measure the measurement radiation and/or a resonator device configured to measure the measurement radiation;
• the strain gauge device is configured to determine an actual strain in a measurement region of the mirror based on an actual deformation of the optical surface;
• the path length device is at least partly arranged in the substrate element;
• the waveguide is at least partially arranged in the substrate element;
• the closed-loop control device comprises a closed loop configured to set a target strain of the measurement region via the actuator taking into account the actual strain of the measurement region determined by the strain gauge device;
• the closed-loop control device is configured to correct a temperature-induced deviation of the actual deformation of the optical surface from a target deformation of the optical surface and/or a strain-induced deviation of the actual deformation of the optical surface from the target deformation of the optical surface;
• and
• the substrate element comprises SiO2—TiO2 glass.