Hedser H. van Brug

Nanometer deep shaping with fluid jet polishing

We describe the theoretical dependence of various important parameters of the fluid jet polishing process on the material removal rate: the processing time, abrasive concentration, abrasive diameter, particle velocity, and the effect of scanning. Some recent experiments are described that prove that it is possible to remove very small amounts of material, less than 1 nm/min, using either short processing times or an appropriate slurry. The removal spot in the stationary case is compared to that in the translational case both theoretically and experimentally. From both a theoretical and an experimental point of view it is shown that the removal is in the ductile regime.

Zernike polynomials as a basis for wave-front fitting in lateral shearing interferometry.

A new method for handling Zernike polynomials is presented. Owing to itsnefficiency, this method enables the use of Zernike polynomials as a basis fornwave-front fitting in shearography systems. An excerpt of anC++ class is presented to show how thenpolynomials are calculated and represented in computernmemory.

Phase-step calibration for phase-stepped interferometry.

A novel method to set the proper phase steps, as used in phase-stepped interferometry, is presented. It is indicated how and when this method can be used. With only two images one can deduce the relative phase step between them by calculating the correlation between the two images. The error of the proposed method is shown to be smaller than 0.1%.

Polarization phase stepping with a Savart element

The imaging properties of a real-time shearing interferometer are presented. The use of Savart elements, both as a beam displacer and an analyzer in a polarization phase-stepping scheme, is demonstrated in a real-time, two-camera, four-bucket shearing interferometer. A simple calculation scheme for ray propagation through uniaxial, birefringent elements is presented, and the effects on the image formation through 6-cm-long Savart elements is discussed.

Temporal phase unwrapping and its application in shearography systems.

Temporal phase unwrapping is applied to a two-camera polarization phase-stepped system. A simple algorithm for the phase-change calculation is given, together with simulations, to indicate its validity and strength. This method can be applied directly for detection of phase changes as a function of time. It is proposed to use this method in a shearography setup. The phase distribution in the shearogram can then be obtained, without the standard 2π ambiguities, by application of the required total shear in a number of smaller steps, provided that each step is small enough to be free from these 2π phase steps.

Nanometer accurate shaping with fluid jet polishing

This article describes the Fluid Jet Polishing process. An overview of the theoretical dependence of various important parameters is given. We discuss some results obtained with FJP, including typical material removal rates and roughness values. Some recent experiments are described that show that it is also possible to obtain removal rates as small as one nanometer per minute for glass surfaces. Specific surface profiles are created, both with and without the use of surface protecting masks.

Fluid jet polishing: removal process analysis

This paper reports on a new finishing process, Fluid Jet Polishing (FJP), that resembles the kinetic process employed in ASJ systems in that it is guiding a pre-mixed slurry to the surface, but within FJP low pressures are applied. Since FJP employs a fluid for machining, no tool wear occurs and the tool is cooling and removing debris in process. Using slurry that contained water with grinding abrasives, the FJP finishing process has been demonstrated. On flat glass samples, the surface roughness of a previously ground surface has been reduced from 475 nm rms to 5 nm rms and a prepolished surface has been shaped without increasing its roughness of 1.6 nm rms. Experiments are described showing that the final surface roughness depends on slurry characteristics and that the material removal spot can be adjusted by varying process parameters, e.g. the angle of the incident ray.

Novel approaches to generate aspherical optical surfaces

This paper gives a methodological analysis of abrasive Optical Fabrication Techniques that apply an abrasive contact between tool and workpiece for the generation of refractive and reflective (a) spherical optical surfaces. Optical Fabrication Techniques comprise the following two functioning elements: the used Material Removal Process (MRP, e.g. fresh feed polishing) and the applied Shaping Method (SM, e.g. based on surface evolution calculations). Important MRPs and SMs are reviewed. Subsequently, state-of-the-art optical fabrication techniques will be discussed representing existing combinations of MRPs and SMs. Finally, it will be shown, that new optical fabrication techniques can be developed either by inventing new MRPs or SMs, or by creating new combinations of existing MRPs and SMs.

On the effective wavelength in two-wavelength interferometry

A discussion on the effective wavelength in two-wavelength interferometry is given. A definition, different from the commonly adopted one, is presented and its validity is discussed. By adopting this new effective wavelength the range over which lengths can be measured using interferometric techniques can be vastly increased, without introducing phase unwrapping ambiguities within this increased range. A graph is presented from which a method is derived, enabling an efficient use of this new effective wavelength.

Speckles and their effects in spectrometers due to on-board diffusers

Earth observation satellites are commonly equipped with an on-board diffuser. Their use will be pointed out and the errors associated with their use will be explained. The origin of the errors, the speckles formed by scattering on the diffusers, will be dealt with in detail and solutions to minimize these errors will be presented. The use of diffusers, and the types of diffusers will be discussed in combination with their ability to minimise the contrast of the spectral features.