Ferrofluid mirror

Ferrofluid mirror telescopes have been built to obtain astronomical data and used to take images of deep space; subjects for research include exoplanets. The main challenge astronomers and scientists face is image distortions due to wavefront errors caused by the atmosphere. The solution to this problem is to create mirrors with controllable surface shapes, known as deformable mirrors.^[6] Ferrofluid mirrors are used as deformable mirrors because when ferrofluids are exposed to a magnetic field, the liquid forms a shape to minimize the energy of the system which involves magnetic, gravitational, and surface tension forces of the liquid.^[2]

While ferrofluid mirrors are widely used in telescopes, ferrofluid mirrors might also be applied in the field of visual science. Human eyes suffer from many optical imperfections. Ophthalmologists look into the eyes to detect and diagnose diseases by examining the retina. Ferrofluid mirrors could be rapidly adjusted to compensate for the large distortions in diseased eyes during eye exams or treatments.^[7] They can generate surfaces having complex shapes, and thus can be used to determine the shape of the lens of the human eye, the crystalline lens. This may allow the measurement of high-order aberrations of the crystalline lens so that they can be corrected with appropriate medical procedures. The magnetically shaped reference surface would further be used to verify the correction made to the lens of the eye before, during or after the procedures.^[8]

Before ferrofluid mirrors were invented, solid deformable mirrors were used to correct atmospheric distortion and keep a steady focus. Deformable solid mirrors use flexible mirrors with complex actuators underneath to correct for atmospheric distortion and keep a steady focus.^[9] Shortcomings of traditional deformable solid mirrors include cost, fragility, and the need for continuous power. Images from these mirrors have an undesirable quilt pattern due to the discrete actuators beneath the mirror surface.^[6]

Mercury was used as the main material of early deformable liquid-mirror telescopes because of its high reflectivity and low melting temperature. However, as a magnetic liquid, it had problems. It is difficult to obtain a stable metallic based magnetic liquid, and the high density of mercury necessitates a larger deforming force and thus a strong magnetic field.^[5]

The limitations associated with the use of mercury for deformable liquid mirrors can be solved through the use of ferrofluids. Ferrofluid mirrors use cheaper materials, and are able to make more corrections due to its larger range of motion. Stable ferrofluids have wide ranges of physical properties thus can be produced to suit many practical application needs.^[9]