Mr. Alexander Haberl Profile

Alexander Haberl

at Technische Hochschule Deggendorf

SPIE Involvement:

Conference Chair | Editor | Author

Proceedings Article | 18 August 2018 Paper

Model based error separation of power spectral density artefacts in wavefront measurement

Alexander Haberl, Antonia Harsch, Gerald Fütterer, Johannes Liebl, Christof Pruß, Rolf Rascher, Wolfgang Osten

Proceedings Volume 10749, 107490T (2018) https://doi.org/10.1117/12.2321106

KEYWORDS: Interferometers, Wavefronts, Calibration, Phase transfer function, Mirrors, Objectives, Phase measurement, Fizeau interferometers, Sensors, Modulation transfer functions

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Proceedings Article | 7 August 2018 Paper

Contribution of the phase transfer function of extended measurement cavities to mid spatial frequencies and the overall error budget

G. Fütterer, J. Liebl, A. Haberl

Proceedings Volume 10829, 108290L (2018) https://doi.org/10.1117/12.2318711

KEYWORDS: Spatial frequencies, Phase transfer function, Sensors, Mirrors, Modulation transfer functions, Fizeau interferometers, Interferometers, Phase measurement, Point spread functions, Stars

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A challenge of coaxial - measurement cavity based - interferometer is to realize an interference contrast in the vicinity of one and to realize a complete elimination of the parasitic reflections. Another challenge, which also exists in non-coaxial setups, is the phase transfer function of extended measurement cavities. Ideally, the surface under test (SUT) and the reference surface (REF) are both exactly imaged onto the detector plane. In practice, SUT and REF have to be placed within the depth of field (DOF), which refers to the object space. The term depth of focus refers to the image space. To avoid confusion, the depth of field might be referred to as DOOF (depth of object field) and the depth of focus might be referred to as DOIF (depth of image field).

However, in many measurement situations, the REF is not placed within the DOOF, which is the small z-range, which is imaged onto the detector plane. Furthermore, the phase transfer function (PTF) of the REF and the image distortion of the REF are both dependent on the focal plane used to image the SUT onto the detector plane. Effects as phase deformation, image distortion and image blurring have to be taken into account when using extended measurement cavities. This can be done by using a look up table (LUT), which contains simulated and/or calibrated data. Thus, the related system error can be subtracted. A remaining challenge is an unknown object under test (OUT), which is measured by using a double path arrangement. The measured wave front depends on the two surfaces of the OUT and the position of the return mirror. For simplicity, a homogeneous substrate and a perfect return mirror might be presumed. The simulation of waves propagating within extended measurement cavities, as well as measurement results, will be discussed. In addition, the influence on the power spectral density (PSD) will be described. This is important for high end correction techniques as e.g. magneto rheological figuring (MRF) and ion beam figuring (IBF).

Proceedings Article | 7 August 2018 Paper

Tilted wave interferometry for testing large surfaces

Antonia Harsch, Christof Pruss, Alexander Haberl, Wolfgang Osten

Proceedings Volume 10829, 1082908 (2018) https://doi.org/10.1117/12.2318573

KEYWORDS: Interferometers, Aspheric lenses, Optical spheres, Wavefronts, Interferometry, Computer generated holography, Spherical lenses, Time metrology, Beam splitters, Microlens array

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Proceedings Article | 7 August 2018 Paper

ABC-polishing

Alexander Haberl, Johannes Liebl, Rolf Rascher

Proceedings Volume 10829, 1082906 (2018) https://doi.org/10.1117/12.2318549

KEYWORDS: Polishing, Zernike polynomials, Tolerancing, Magnetorheological finishing, Databases, Spherical lenses, Surface finishing, Ion beams, Ion beam finishing, Manufacturing

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In the past, steadily increasing demands on the imaging properties of optics have led more and more precise spherical apertures. For a long time, these optical components have been produced in a satisfying quality using classic polishing methods such as pitch polishing. The advance of computer-controlled subaperture (SA) polishing techniques improved the accuracy of spheres. However, this new machine technology also made it possible to produce new lens geometries, such as aspheres.

In contrast to classic polishing methods, the high determinism of SA polishing allows a very specific correction of the surface defect. The methods of magneto-rheological finishing (MRF) [1], [2] and ion beam figuring (IBF) [3], [4] stand out in particular because of the achievable shape accuracy. However, this leads to the fact that a principle of manufacturing "As exact as possible, as precise as necessary" [5] is often ignored. The optical surfaces often produced with unnecessary precision, result at least in increased processing times.

The increasing interconnection of the production machines and the linking with databases already enables a consistent database to be established. It is possible to store measurements, process characteristics or tolerances for the individual production steps in a structured way. The difficulty, however, lies in the reasonable evaluation of the measurement data.

This is where this publication comes in. The smart evaluation of the measurement data with the widespread Zernike polynomials should result in a classification, depending on the required manufacturing tolerance. In combination with the so-called ABC analysis, all surface defects can be categorized. In this way, an analytic breakdown of a - initially confusing - overall problem is made. With the aid of cost functions [6] an evaluation and consequently a deduction of actions is made possible. Thus, for example, the isolated processing of rotationally symmetrical errors in spiral mode, setup times and machining times can be reduced while avoiding mid spatial frequency errors (MSFE) at the same time.

Proceedings Article | 15 June 2017 Paper

Polishing tool and the resulting TIF for three variable machine parameters as input for the removal simulation

Robert Schneider, Alexander Haberl, Rolf Rascher

Proceedings Volume 10326, 1032602 (2017) https://doi.org/10.1117/12.2267415

KEYWORDS: Optics manufacturing, Polishing, Analytical research, Glasses, Photovoltaics, Silver, Foam, Optical components, Ion beams, Ion beam finishing, Interferometers

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The trend in the optic industry shows, that it is increasingly important to be able to manufacture complex lens geometries on a high level of precision. From a certain limit on the required shape accuracy of optical workpieces, the processing is changed from the two-dimensional to point-shaped processing. It is very important that the process is as stable as possible during the in point-shaped processing. To ensure stability, usually only one process parameter is varied during processing. It is common that this parameter is the feed rate, which corresponds to the dwell time.

In the research project ArenA-FOi (Application-oriented analysis of resource-saving and energy-efficient design of industrial facilities for the optical industry), a touching procedure is used in the point-attack, and in this case a close look is made as to whether a change of several process parameters is meaningful during a processing. The ADAPT tool in size R20 from Satisloh AG is used, which is also available for purchase. The behavior of the tool is tested under constant conditions in the MCP 250 CNC by OptoTech GmbH. A series of experiments should enable the TIF (tool influence function) to be determined using three variable parameters. Furthermore, the maximum error frequency that can be processed is calculated as an example for one parameter set and serves as an outlook for further investigations. The test results serve as the basic for the later removal simulation, which must be able to deal with a variable TIF. This topic has already been successfully implemented in another research project of the Institute for Precision Manufacturing and High-Frequency Technology (IPH) and thus this algorithm can be used.

The next step is the useful implementation of the collected knowledge. The TIF must be selected on the basis of the measured data. It is important to know the error frequencies to select the optimal TIF. Thus, it is possible to compare the simulated results with real measurement data and to carry out a revision. From this point onwards, it is possible to evaluate the potential of this approach, and in the ideal case it will be further researched and later found in the production.

Proceedings Article | 15 June 2017 Paper

Yet one more dwell time algorithm

Alexander Haberl, Rolf Rascher

Proceedings Volume 10326, 1032606 (2017) https://doi.org/10.1117/12.2270540

KEYWORDS: Polishing, Ion beam finishing, Manufacturing, Mirrors, Surface finishing, Beam shaping, Ion beams, Electromagnetic coupling, Convolution, Deconvolution, Image processing, Algorithm development

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The current demand of even more powerful and efficient microprocessors, for e.g. deep learning, has led to an ongoing trend of reducing the feature size of the integrated circuits. These processors are patterned with EUV-lithography which enables 7 nm chips [1]. To produce mirrors which satisfy the needed requirements is a challenging task.

Not only increasing requirements on the imaging properties, but also new lens shapes, such as aspheres or lenses with free-form surfaces, require innovative production processes. However, these lenses need new deterministic sub-aperture polishing methods that have been established in the past few years. These polishing methods are characterized, by an empirically determined TIF and local stock removal.

Such a deterministic polishing method is ion-beam-figuring (IBF). The beam profile of an ion beam is adjusted to a nearly ideal Gaussian shape by various parameters. With the known removal function, a dwell time profile can be generated for each measured error profile. Such a profile is always generated pixel-accurately to the predetermined error profile, with the aim always of minimizing the existing surface structures up to the cut-off frequency of the tool used [2].

The processing success of a correction-polishing run depends decisively on the accuracy of the previously computed dwell-time profile. So the used algorithm to calculate the dwell time has to accurately reflect the reality. But furthermore the machine operator should have no influence on the dwell-time calculation. Conclusively there mustn’t be any parameters which have an influence on the calculation result. And lastly it should take a minimum of machining time to get a minimum of remaining error structures. Unfortunately current dwell time algorithm calculations are divergent, user-dependent, tending to create high processing times and need several parameters to bet set.

This paper describes an, realistic, convergent and user independent dwell time algorithm. The typical processing times are reduced to about 80 % up to 50 % compared to conventional algorithms (Lucy-Richardson, Van-Cittert …) as used in established machines. To verify its effectiveness a plane surface was machined on an IBF.

Proceedings Article | 27 August 2015 Paper

Surface errors in the course of machining precision optics

H. Biskup, A. Haberl, R. Rascher

Proceedings Volume 9575, 95750O (2015) https://doi.org/10.1117/12.2189991

KEYWORDS: Surface finishing, Spatial frequencies, Polishing, Linear filtering, Error analysis, Ion beam finishing, Precision optics, Optics manufacturing, Manufacturing, Interferometry

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