Continuous photo-controlled deformable mirror

We have developed photo-controlled deformable mirrors (PCDM) for spatial light modulation and wavefront control making use of three different photoconductor wafers: silicon (Si), zinc sulphide (ZnS) and cadmium sulfide (CdS). The devices are a membrane mirror based on a 1-inch monolithic non-pixelated photoconductive substrate with a transparent ITO electrode on one side coupled with a 5 mu m thick nitrocellulose membrane. The devices are driven applying DC or AC voltage and are characterized by measuring the generated wavefront using a Shack-Hartmann wavefront sensor. The fabrication and characterization of these deformable mirrors are reported. The cadmium sulfide based PCDM did not work properly because has been noticed a memory effect after the illumination that faded in hours. For the zinc sulphide based PCDM the maximum deformation achieved is approximately 4.7 mu m PtV (wavefront), with a deformation very stable, but considering that the ZnS photoconductor shows very low charge mobility and very high internal resistance it is suitable for making a PCDM working in DC with a memory effect that can be switched in a time frame of seconds and can carry the deformation for a long time compensating for long time wavefront drifts. For the silicon based PCDM, upon uniform illumination with a NIR LED, the deformation increases with the voltage applied, its frequency and the light intensity. The maximum deformation achieved is approximately 2 mu m PtV. The repeatability of the induced deformation is also evaluated together with its time stability, proving that the device is reliable in the working conditions. The response time is evaluated and it is in the range of 10 ms, this device is suitable for an efficient adaptable focusing element with an important focus control.