Silicon Carbide (SiC) mirrors hold many advantages over traditional optical materials and are increasingly common in optical systems. The wide range of optical applications necessitates different approaches to the manufacturing and finishing of SiC mirrors. Three key advancements have led to this differentiation: 1) manufacturing of CVD clad SiC mirrors in near cost and schedule parity with Zerodur, 2) super-polish of amorphous Silicon claddings, 3) low-roughness polishing results of bare reaction-bonded SiC aspheres. Three approaches which utilize these advancements will be discussed, each with its own strengths and weaknesses for specific applications. The relative schedules and performance of these approaches will also be compared, with Zerodur used as a reference.
We will discuss mid-spatial frequency (MSF) optical surface errors, and how they affect
optical performance of an optical system, including contrast, ensquared energy and pixel cross-talk. MSF
errors will be represented in terms of Power Spectral Density (PSD), and examples will be discussed
where PSD is well controlled and poorly controlled. We will show recent examples of PSDs of aspheric
mirrors, sometimes with very challenging aspheric departure or other attributes, as routinely finished
Tinsley, and suggest ways the designer can effectively specify an optic for smoothness.