The mechanical properties of silicon carbide make it a perfect material for the substrate in a galvo scanning mirror, but the optical properties of the surface are a major downside. Achieving high reflectance for energy conservation, similar to what can be achieved on fused silica substrates, requires an intelligent approach to control the surface’s roughness. As mentioned above, straightforward polishing would be a very long, inefficient, and expensive process, so Altechna decided to go with the process we do best – coating.

Smoothing out the surface

Altechna’s approach to this challenge comprises optimized sub-layer deposition and a polishing procedure before the application of a low-loss reflective coating. Naturally, the coating process cannot be tailored to purposefully fill the biggest cavities to smooth out the base for low-loss mirrors. However, with a sufficient deposited material layer, followed by an optimized polishing procedure, the surface of the component is no longer covered in holes that would induce irradiation losses in the actual mirror.

Low-loss UV mirror solution

After modifying the surface of the SiC substrate, it was time for Altechna to provide our best dielectric coating solution for a UV low-loss mirror. As can be seen in Figure 4, we have managed to reach over 99.5% reflectance at 355 nm at a 0° angle – equal within the margin of error to the reflectance of the same coating on a standard UVFS substrate. Another proof of the base modification’s advantage is the RMS roughness of the modified surface with dielectric HR coating. Because of the sub-layer, the roughness drops from 4.72 nm on unmodified SiC + HR to 0.8 nm on modified SiC + HR and that evidently correlates with lower losses and improved spectral performance.

BROCHURE: https://shorturl.at/alnOV