REO has introduced a new line of superpolished laser mirrors, offering substantially lower loss than previously available, suitable for the most demanding applications. Specifically, microroughness on these mirrors is below 0.5Å, allowing them to achieve a scattering loss of under 5ppm and a finesse of 200,000 when incorporated into optical cavities. In contrast, most commercially available superpolished mirrors only reach 100ppm of loss and a finesse in the 30,000 range. Ion beam sputtered coatings (IBS) are employed to take full advantage of these ultra-smooth surfaces and deliver reflectivities of over 99.998 per cent at any wavelength in the 450nm to 2µm range.
REO superpolished mirrors can be produced on a number of different substrate materials, including BK7, fused silica, Zerodur, ULE, sapphire and silicon. They are supplied with diameters in 0.25-inch to 4.0-inch (6mm to 101mm) range, with a flatness of λ/20 (at 633nm), 10-5 surface quality over an 80 per cent clear aperture, with zero defects (0-0) achievable over controlled sub-apertures. Furthermore, it is possible to use standard, solvent based cleaning methods and still maintain these exceptional loss specifications. Mirrors with plano, concave and convex surface shapes are all available. REO utilises a suite of advanced metrology instrumentation to maintain and verify these performance specifications, including phase shifting interference microscopy, cavity ringdown measurements and photothermal common path interferometers.
These superpolished mirrors are useful in any laser or laser-based system which demands extremely high reflectivity or very low loss. Typical applications are as cavity mirrors in low gain gas and solid state lasers, such as HeNes and HeCds, and in systems which employ non-linear processes. Other important uses are in ring laser gyroscopes (RLG), instruments based on cavity ringdown spectroscopy and frequency reference standards.