Adaptive optical module for a microlithographic projection exposure apparatus

A module, comprising:

• an optical surface configured to interact with exposure radiation of a projection exposure apparatus;
• and
• a plurality of actuators configured to change a shape of the optical surface;
• a dielectric medium configured to deform when an electrical voltage is applied thereto;
• a plurality of separate control electrodes;
• a weakly conductive structure having an electrical conductivity of at least 0.1 mS/m;
• and
• an evaluation device,
• wherein:
• each actuator has a corresponding control electrode configured to generate an electric field in a layer of the dielectric medium;
• the control electrodes are connected to one another via the weakly conductive structure;
• and
• the evaluation device is configured so that, when measuring an impedance of one of the actuators, the evaluation device computationally extracts from the measurement result an effect, influencing the measurement result, of a current flow between the corresponding control electrode and at least one of the other control electrodes, the current flow being caused by the weakly conductive structure.

A method of ascertaining a respective deflection of a plurality of actuators of an adaptive optical module of a microlithographic projection exposure apparatus, the actuators configured to change a shape of an optical surface of the optical module, the adaptive optical module comprising a dielectric medium which is deformable by an electrical voltage, each actuator having a separate control electrode to generate a respective electric field in a layer of the dielectric medium, control electrodes being connected to one another by a weakly conductive structure having an electrical conductivity of at least 0.1 mS/m, the method comprising:

• measuring an impedance of an actuator;
• computationally extracting an effect of a current flow caused by the weakly conductive structure from the measurement result of the impedance measurement, wherein the current flow takes place between the control electrode of the actuator being measured and at least one further of the control electrodes;
• and
• calculating the respective deflection of the actuators from the respective measured impedance.