Aberration correction with a magnetic liquid active mirror

We investigate active magnetic liquid mirrors and their use for the correction of non-axisymmetrical aberrations (like third-order coma and astigmatism). We are mainly concerned with their application to the correction of the severe aberrations of a telescope observing at large angles from the optical axis of its primary mirror. We performed numerical simulations showing that it is possible to generate third- and fifth-order coma and astigmatism by applying electrical currents to simple networks of copper wires. These wire networks generate a magnetic field that can deform the surface of a magnetic liquid (ferrofluid) to a desired optical surface. We present the results from laboratory tests on a prototype mirror demonstrating third-order coma and astigmatism. We show that it is possible to correct non-axisymmetrical aberrations by using an active ferrofluidic mirror. This novel type of deformable mirror could be used to correct the aberrations present in many optical systems, particularly in zenith telescopes, like liquid mirror telescopes, rendering them far more versatile and powerful.