Deformable mirrors based on magnetic liquids

The trend towards ever larger telescopes and more advanced adaptive optics systems such as multi-conjugate adaptive optics is driving the need for deformable mirrors with a large number of low cost actuators. Other applications require strokes larger than those readily available from conventional mirrors. Magnetically deformable liquid mirrors are a potential solution to both these problems. Depositing a thin silver colloid known as a metal liquid-like film (MELLF) on the ferrofluid surface solves the problem of low reflectivity of pure ferrofluids. This combination provides a liquid optical surface that can be precisely shaped in a magnetic field. We have demonstrated a reflective coating that is stable for more than 30 days with a reflectivity of 50% to in the near infrared. Additional experiments indicate that MELLF coatings can provide near infrared reflectivity values in excess of 80%. We also report on recent response time measurements of liquid deformable mirrors. We have demonstrated liquid mirror actuators with slew rates of 800 mums, corresponding to an actuator bandwidth of approximately 40 Hz and 80 Hz for strokes of 10 mum and 5 mum respectively.