Background
Water-soluble crystalline materials have become ubiquitous as critical optics in a wide variety of laser systems. These optics are commonly used for frequency conversion, polarization control, laser gain media and transparent windows in the infrared and ultraviolet regimes. However, due to the challenges presented by grinding and polishing water-soluble materials, limited commercial methods and consumables are available for producing optical quality surfaces from these materials. These methods generally include single-point diamond turning and nonaqueous, lap polishing with abrasive grains such as ceria or alumina. Although these methods are considered state-of-the-art, they pose significant drawbacks such as ripple structures on the optical surface, higher roughness than can be achieved with glass optics and residual adhesion of the abrasive particles. Residual abrasives that cannot be cleaned from the surface contribute to lower optical quality through scattering losses as well as reduced laser-induced damage thresholds of the optic when used in high-power laser applications.
Technology Overview
Researchers have invented a method to fabricate and use surface-modified abrasive powders for polishing water‐soluble optical crystals in a nonaqueous medium. The process uses commercially available metal oxide nanoparticles and modifies their surface to become strongly hydrophobic. There is no limitation to the choice of nonaqueous liquid nor to the percentage of abrasives in the formulation. The method of polishing can be planetary (whole optic) polishing using a lap or sub-aperture, where only a small area of the optic is polished at once by a method such as fluid jet polishing or magnetorheological finishing.
Benefits
Modification of abrasives by this method offers reduced adhesion of the particles to the optical crystals during the polishing process. This benefit improves post-polishing cleanability-and resulting optical quality-and improved laser-induced damage thresholds. Furthermore, surface-modified abrasives demonstrate improved dispersibility and improved stability of the particle size distribution in nonaqueous oils. These features facilitate the polishing process by reducing the sedimentation rate of the particles as well as reducing agglomeration which can result in surface scratches.
Applications
Optical polishing
Opportunity
The University of Rochester seeks to license this technology exclusively.