Magnetorheological finishing (MRF®) is a deterministic polishing process. Typically, an MRF polishing cycle is used to improve the figure of an optical surface (e.g. reduce the irregularity of a spherical surface to λ/20 PV). The hitmap for this process is based off of a surface (reflection) measurement. However, because MRF polishing is a subaperture process, it is not limited to producing perfectly flat or perfectly spherical surfaces. Indeed, the polishing process can converge to any desired surface shape. This is a particularly useful, enabling feature that can be used to perform transmitted wavefront corrections.
One method to produce a perfect transmitted wavefront is to polish perfect surfaces throughout the system, which assumes perfect material homogeneity. In some instances, this can also be accomplished by measuring the transmitted wavefront of an imperfect system, and correcting it by polishing a compensating surface shape into a single surface. By correcting transmitted wavefront data, rather than a surface measurement, this can be a fairly straightforward process. This process can correct for material inhomogeneities, improve system tolerances, and correct prism angles.
This paper will begin by giving an overview of transmitted wavefront tests. It will explain how this data can be used to perform a correction by an MRF polishing cycle. Finally, we present some results from corrections of optical systems such as laser rods and prisms.