Surface Microroughness of Optical Glasses

The Center for Optics Manufacturing (COM) at the University of Rochester has made significant advances in the fabrication of precision optical components using deterministic microgrinding with rigid, computer-controlled machining centers and high-speed tool spindles. In deterministic microgrinding, the infeed rate of the microgrinding tool across the optical workpiece is optimized and controlled. This leads to precise knowledge of the amount of removed material when microgrinding optical glasses. This method has been applied to manufacturing convex and concave spherical surfaces with radii 5 mm to ∞ (i.e., planar), and work diameters from 10 to 150 mm have successfully been formed.1–5 Aspherical surfaces have also been manufactured. After less than 5 min of deterministic microgrinding, the resulting specular surfaces have typical rms microroughness of less than 20 nm, 1 μm of subsurface damage, and a surface figure better than 1/2 wave peak to valley.6 Typical infeed rates are 6 to 10 μm/min with 2to 4-μm bound-abrasive diamond tools.