Graded reflectivity mirrors

REO has introduced a new series of graded reflectivity mirrors, enabling precise spatial shaping of both the intensity and phase characteristics of laser beams. In graded reflectivity mirrors, the reflectivity and/or phase effects of the coating vary radially across the surface of the optic. REO can produce these mirrors with virtually any arbitrary variation, including non-rotationally symmetric patterns, as well as with complex designs in which the reflectivity increases and decreases repeatedly across the component.

The most common application for graded reflectivity mirrors is as cavity optics in unstable resonator lasers. In this case, the use of a second order Gaussian or super-Gaussian (Gaussiann) reflectivity profile allows maximum power extraction from the resonator, as well as a smooth far field output beam profile. A Gaussian profile mirror can also be used to achieve laser output with a uniform irradiance distribution, which is often required in illumination, materials processing and surgical applications. The ability to shape the phase of a laser’s emergent wavefront can aid in achieving better focusing characteristics, and can also improve coupling efficiency into optical fibres.

REO offers the graded reflectivity mirrors on a wide range of substrate materials, including fused silica, various optical glasses, ZnSe, ZnS and Si, for operation over the 266nm to 5µm spectral range. The mirrors are available with diameters from 0.25-inches (6mm) to 5-inches (127mm). Reflectivity pattern variations can be achieved down to a scale of approximately 1mm. The use of ion beam sputtering (IBS) coating technology makes these optics suitable for intracavity laser use, and provides a combination of high damage threshold, spectral stability, environmental stability and mechanical durability that makes them compatible with use in demanding environments.