O.W. Fähnle

Fluid jet polishing of optical surfaces

We present a new finishing process that is capable of locally shaping and polishing optical surfaces of complex shapes. A fluid jet system is used to guide a premixed slurry at pressures less than 6 bars to the optical surface. We used a slurry comprising water and 10% #800 SiC abrasives (21.8 mum) to reduce the surface roughness of a BK7 sample from 350 to 25 nm rms and to vary the shape of a polished sample BK7, maintaining its surface roughness of 1.6 nm rms, thereby proving both the shaping and polishing possibilities of the presented method.

Generation of on-axis and off-axis conic surfaces of revolution by applying a tubular tool

A new technique, fabrication of aspherical ultraprecise surfaces using a tube, is applied to the generation of conic surfaces of revolution, which also demonstrates that it is possible to generate different kinds of surfaces with the same tube. Surfaces are considered that are generated with the same tube with an elliptical edge but with different off-axis distances and different angles between the tube and the surface. Subsequently it is shown that the generated surface is always a radial section of a conic surface. In addition it is proven that the shape of the generated conic surface is independent of the off-axis distance. With each elliptical tube edge a range of different conic surfaces can be made depending on the angle between tube and surface. The more the tube edge resembles a circle, the larger will be the range of different surfaces. For each tube an angle between the tube and the surface exists at which it generates an on- or off-axis part of a semi-ellipsoid. Finally, an optimization technique is presented for the determination of the best combination of process-determining parameters for the generation of a certain conic surface.

Loose abrasive line-contact machining of aspherical optical surfaces of revolution.

A new fabrication technique for the generation of optical aspherical surfaces of revolution is presented. This fabrication technique combines the characteristics of conventional loose abrasive machining with features of high-precision machining tools. A prototype of the machine tool based on this fabrication technique is currently being developed. We describe the characteristics of this method. Fabrication of aspherical ultraprecise surfaces using a tube is a line-contact method for the generation of both on- and off-axis, convex and concave, aspherical surfaces of revolution. It employs a self-correcting process and enables the use of loose-abrasive ductile grinding [Appl. Opt. 30, 2761-2777 (1991)] and subsequent bowl-feed polishing [Appl. Opt. 26, 696-703 (1987); Opt. Eng. 31, 1086-1092 (1992); Appl. Opt. 33, 89-95 (1994)] for the generation of aspherical surfaces.

Quantitative roughness measurements with iTIRM

A new method, iTIRM, is used for quantitative surface roughness measurements of ground and polished surfaces and it is shown to be a useful tool for measuring total surface quality instead of individual roughness parameters.

Kinetic finishing applying a low pressure abrasive slurry jet system

In this paper, a new finishing process, Fluid Jet Polishing (FJP), is presented that is capable of locally shaping and polishing complicated optical surfaces in brittle materials (e.g. glass). Within FJP, a fluid jet system is used to guide a premixed slurry at pressures below 6 bar to the surface. An experiment is described in which a slurry comprising water and 10% #800 SiC abrasives (21.8pm) is used to reduce the surface roughness of a BK7 sample from 350 nm rms to 25 nm rms and to vary the shape of a polished BK7 sample maintaining its surface roughness of 1.6 nm rms.

FAUST and WAGNER: Producible shapes

The generation of off-axis parts of rotationally symmetric surfaces applying FAUST and WAGNER is analyzed showing that there are often two fabrication processes possible. The producible surface shapes are discussed showing the possibility of producing optical surfaces performing several functions in a single production step.

Determination of the Optimum Starting Surface for the Generation of Aspherical Surfaces of Revolution

We present a method to obtain the optimum surface shape for use as a starting point for the machining of aspherical surfaces of revolution. Applying this method, the volume that remains to be machined away can be set below an acceptable value. Subsequently, it is shown how this method can be applied for conic surfaces.