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ESO’s ultra-fast wavefront sensor unveils the mysteries of deformable mirrors’ temporal behaviour

During the past years, ESO developed an ultra-fast Shack Hartman (SH) WaveFront Sensor (WFS) based on using a highspeed camera at framerates as high as 16 kHz. This WFS has been used to characterize the sub-ms spatio-temporal behaviour of Deformable Mirrors. This paper reports about the results obtained with micro voice coil actuated Deformable Mirrors. At sampling rates up to 16 kHz fast transients of the full surface can be measured allowing for detailed characterization and modelling of the mirrors’ spatio-temporal behaviour. When an optical phase step is applied to an actuator it triggers a wave travelling across the surface to the edges and then reflected. Using the fast WFS developed by ESO, it has been possible to visualize and characterize this transient phenomenon. Based on these experimental observations, different feed forward control techniques are designed and their efficiency to improve the actuators temporal behaviour and reduce the amplitude of the parasitic surface waves are compared.