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NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenIPH Teisnach

Beitrag (Sammelband oder Tagungsband)

Gerald Fütterer

Optimization of the complex coherence function for diffraction-based wavefront transformations

Unconventional Optical Imaging

2018

ISBN: 9781510618800

DOI: 10.1117/12.2307245

Abstract anzeigen

Partial coherence is used in a plurality of applications, magnifying microscopic imaging, interferometric measurement, lithographic imaging, CGH based wave front shaping, interference lithography and space-bandwidth-limited wave front reconstruction, just to name a few. In some applications the primary light source is characterized by a limited coherence length and an extended angular spectrum of plane waves, which has to be narrowed, e.g. if an Excimer laser is used. Sometimes the angular spectrum of plane waves of the primary light source has to be increased in order to be practical. There are several possibilities in general, the primary light source can be used directly, the system has to be adapted or the coherence function Γ has to be tailored in order to provide the specific requirements. Almost all embodiments come with little changes of the light sources coherence properties only. For example, to use a spectral bandpass filter or to limit the size of the light source seem to be the standard solution for almost everything. However, more advanced tailoring of the complex valued coherence function Γ leads to an increased image quality, e.g. in interferometers, but is not limited to this, reduces background noise, decouples Fizeau cavities or it enables complete new illumination and imaging system designs, which provide unique features. This aspect will be discussed herein. Furthermore, the propagation of the complex coherence will be taken into account. This is done in order to provide defined conditions in defined planes of imaging devices. In other words, the usage of the Wiener-Khintchin theorem and the van Cittert-Zernike theorem is just a part of the system analysis and system optimization, which has to be done. Although generic approaches are used, discrete light source layouts are strongly related to the discrete optical devices, which make use of them. The specific tailoring of the complex coherence function, which is related to the space-bandwidth-limited reconstruction of wave front segments, which also can be referred to as space-bandwidth-limited CGH reconstruction, will be described in more detail. For this type of real time dynamic imaging two major problems - among several others - have to be solved. One problem is the huge computation power and the other one is the coherent retinal cross talk of adjacent image points, which are reconstructed in the image volume. The disclosed layouts of tailored secondary light sources are based on the Wiener-Khintchin theorem and the van Cittert-Zernike theorem. Both problems, which are mentioned above, can be solved. Tailored complex valued light sources reduce the required computation power by enabling reduced coherent overlay of sub-CGH areas. Furthermore, they reduce the coherent retinal cross talk of dynamic real time spacebandwidth- limited CGH reconstruction, which is used in advanced imaging applications, too. This results in an increased image quality of partial coherent wave field reconstruction based imaging.

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Beitrag (Sammelband oder Tagungsband)

Load controlled process window analysis of feed controlled CNC grinding

PROCEEDINGS VOLUME 10692 SPIE OPTICAL SYSTEMS DESIGN, 14-17 MAY 2018 Optical Fabrication, Testing, and Metrology VI, Frankfurt, Germany

2018

ISBN: 978-1-5106-1921-0

DOI: 10.1117/12.2315336

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Beitrag (Sammelband oder Tagungsband)

Ductile grinding of tungsten carbide applying standard CNC machines: a process analysis

Proceedings of SPIE 10692: SPIE Optical Systems Design/Optical Fabrication, Testing, and Metrology VI (14.-17.05.2018; Frankfurt/Main)

2018

DOI: 10.1117/12.2315338

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Beitrag (Sammelband oder Tagungsband)

Filled-Up-Microscopy (FUM): a non-destructive method for approximating the depth of sub-surface damage on ground surfaces

Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach])

2018

ISBN: 978-1-5106-2270-8

DOI: 10.1117/12.2318576

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Beitrag (Sammelband oder Tagungsband)

Ductile mode single point diamond turning (SPDT) of binderless tungsten carbide molds

Proceedings of SPIE Optical Engineering + Applications (19-23 August, 2018; Optical Manufacturing and Testing XII; San Diego, CA, USA), San Diego, United States, vol. 10742

2018

ISBN: 978-1-5106-2055-1

DOI: 10.1117/12.2323244

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Beitrag (Sammelband oder Tagungsband)

From turning to grinding: ductile machining with gPVA

Proceedings of SPIE Optical Engineering + Applications (19-23 August, 2018; Optical Manufacturing and Testing XII; San Diego, CA, USA), San Diego, United States, vol. 10742

2018

ISBN: 978-1-5106-2055-1

DOI: 10.1117/12.2323246

NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenIPH Teisnach

Beitrag (Sammelband oder Tagungsband)

Ductile grinding of tungsten carbide molds applying standard CNC machines

Proceedings of SPIE Optical Engineering + Applications (19-23 August, 2018; Optical Manufacturing and Testing XII; San Diego, CA, USA), San Diego, United States, vol. 10742

2018

ISBN: 978-1-5106-2055-1

DOI: 10.1117/12.2323245

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Beitrag (Sammelband oder Tagungsband)

Closed-loop next generation laser polishing

Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach])

2018

ISBN: 978-1-5106-2270-8

DOI: 10.1117/12.2318749

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Beitrag (Sammelband oder Tagungsband)

SPDT and standard CNC-grinding of tungsten carbide molds for precision glass molding: an experimental process analysis

Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach])

2018

ISBN: 978-1-5106-2270-8

DOI: 10.1117/12.2318710

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Beitrag (Sammelband oder Tagungsband)

gPVA: a system for the classification of grinding tools

Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach])

2018

ISBN: 978-1-5106-2270-8

DOI: 10.1117/12.2318695

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Vortrag

Christian Vogt

Standardized evaluation of grinding tools for brittle and ductile mode grinding

European Optical Society Biennial Meeting (EOSAM) 2018, Delft, Niederlande

2018

Abstract anzeigen

Grinding processes offer a variety of parameters that influence the quality and quantity of the optical elements to be produced. Systematic optimization can also uncover unused potential in "stable and efficient" processes. gPVA (grinding Process Validation Approach) is a system for describing grinding processes. It was first presented in 2017 as a tool for process optimization. gPVA is a method to evaluate different grinding tools in terms of maximum material removal. Therefore, a standardized testing procedure was developed, that can be carried out on standard CNC grinding machines (Fig 1). The data is used to identify parameter sets with valid points of operation with a linear proportion of feed speed and force. In order to evaluate the data independently of cutting speed and tool geometry, a so-called removal rate is calculated. This can essentially be understood as material removal rate.

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Vortrag

In situ laser monitoring of laser polishing

119. Jahrestagung der Deutschen Gesellschaft für angewandte Optik (DGaO), Technische Hochschule Aalen

2018

Abstract anzeigen

A novel fabrication parameter controlling method for laser polishing is presented, measuring within the footprint the smoothening process in real time. Recently, a new method for in situ measuring level of surface roughness has been developed [1] where a HeNe laser beam is being reflected from within the sample at the surface under test and the intensity of its reflected beam is being monitored.In this paper we report on an experimental study where this method has been applied to laser polishing. The internal local surface area under test is chosen to be located at the very spot where the laser polishing footprint is located from the outside of the sample melting its surface locally. Because fused silica is not transparent at the operating CO2 laser wavelength, the intensity of the reflected beam can be monitored enabling an in situ control of the laser polishing process. Consequently, the optimum dwell time can be determined, a footprint needs to stay at a certain point before moving further enabling a more stable and cost optimized polishing. [1] O.Fähnle,“In process monitoring of optics fabrication”, SPIEconference “PrecisionOptics Manufacturing”2017

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Zeitschriftenartikel

Interlaboratory comparison measurements of aspheres

Measurement Science and Technology, vol. 29, no. 5

2018

DOI: 10.1088/1361-6501/aaae96

Abstract anzeigen

The need for high-quality aspheres is rapidly growing, necessitating increased accuracy in their measurement. A reliable uncertainty assessment of asphere form measurement techniques is difficult due to their complexity. In order to explore the accuracy of current asphere form measurement techniques, an interlaboratory comparison was carried out in which four aspheres were measured by eight laboratories using tactile measurements, optical point measurements, and optical areal measurements. Altogether, 12 different devices were employed. The measurement results were analysed after subtracting the design topography and subsequently a best-fit sphere from the measurements. The surface reduced in this way was compared to a reference topography that was obtained by taking the pointwise median across the ensemble of reduced topographies on a $1000 \times 1000$ Cartesian grid. The deviations of the reduced topographies from the reference topography were analysed in terms of several characteristics including peak-to-valley and root-mean-square deviations. Root-mean-square deviations of the reduced topographies from the reference topographies were found to be on the order of some tens of nanometres up to 89 nm, with most of the deviations being smaller than 20 nm. Our results give an indication of the accuracy that can currently be expected in form measurements of aspheres.

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Beitrag (Sammelband oder Tagungsband)

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

Proceedings of SPIE 10749 (SPIE Optical Engineering + Applications Conference on Interferometry XIX [August 19-23, 2018; San Diego, CA, USA])

2018

DOI: 10.1117/12.2321106

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Beitrag (Sammelband oder Tagungsband)

Bare Die Connections via Aerosol Jet Technology for Millimeter Wave Applications

Proceedings of the 48th European Microwave Conference (EuMC)/European Microwave Week (EuMW) 2018 (September 24-28, 2018; Madrid, Spain)

2018

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Beitrag (Sammelband oder Tagungsband)

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

Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach])

2018

ISBN: 978-1-5106-2270-8

DOI: 10.1117/12.2318711

Abstract anzeigen

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).

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Beitrag (Sammelband oder Tagungsband)

DefGO

Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach])

2018

ISBN: 978-1-5106-2270-8

DOI: 10.1117/12.2318704

Abstract anzeigen

The manufacturing of optical lenses has various steps. Generally, the manufacturing can be split up into the following steps: the workpiece is pre-ground with a coarse tool; it is then fine-ground with a finer tool. As the final polishing is a demanding and time-consuming process that cannot manage large removal rations not can it equalise rough shape errors, the starting quality and surface quality needs to be as high as possible. According to the current state of technology, ground lenses must be measured with tactile measuring techniques in order to detect shape errors. This is timeconsuming and expensive, and only two dimensional profiles can be measured. DefGO’s project objective is to introduce deflectometry as a new, three dimensional lens measuring standard. A problem with the application of deflectometry is that the object to be measured has to reflect enough light, which is not the case for ground glass with rough surfaces. DefGO’s solution is to wet the lens with a fluid to create a closed reflecting surface.

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Beitrag (Sammelband oder Tagungsband)

On the metrology of the MSF errors

Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach])

2018

ISBN: 978-1-5106-2270-8

DOI: 10.1117/12.2318675

Abstract anzeigen

The aim of our research is to study middle spatial frequency errors (MSFE) on optical surfaces. We investigate the surfaces after all manufacturing processes to find out the main affecting factors and to choose the proper processing parameters to minimize the size of the errors. In this paper we describe some middle spatial frequency errors, which occur during grinding. As there are limited possibilities to measure ground surfaces, their analysis from the point of measurement is most difficult. Therefore, it is of utmost importance to optimally organize the measurement guaranteeing sufficient data for the reconstruction of the toolpath and avoidance of aliasing effects. In the paper discuss possible classifications and some difficulties during measuring of grinded surfaces.

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Beitrag (Sammelband oder Tagungsband)

Workpiece self-weight in precision optics manufacturing: compensation of workpiece deformations by a fluid bearing

Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach])

2018

ISBN: 978-1-5106-2270-8

DOI: 10.1117/12.2318577

Abstract anzeigen

The effects, the extent and the importance of workpiece deformations, particularly lenses, caused by the weight of the workpiece itself, were examined in a previous paper1 . The considered deformations are in the single-digit to two-digit nanometer range. The investigation was carried out by FEM calculations. The conclusion of the previous aper was that a full-surface support of a workpiece in the processing of one surface presumably produces the best results. Furthermore, it was found that if the second functional surface is not to be touched in the process, a full contact lens mounting on its circumference is advisable. An alternative method for fixing precision lenses is therefore desirable. This can be accomplished in two steps. As a first step, the lens must be gripped at its periphery so that none of the optically functional surfaces of the lens is compromised. However, the complete circumference has to be fixated gaplessly because a punctual fixation has the disadvantage of deforming the lens surface asymmetrically. As a second step, the freely hanging lens surface should be supported to minimize deformation. An approach had to be found that supports the surface like a solid bearing but at the same time does not touch it. Therefore, the usage of an incompressible fluid as a hydrostatic bearing for full-surface support is pursued. For this purpose, the bottom side of the lens has to be stored on water. The results of the FEM simulation showed that with a fluid bearing the resulting deformations can be drastically reduced in comparison to a freely hanging surface. Furthermore, under the right conditions, a resulting deformation comparable to a full surface solid support can be achieved. The content of this paper is a test series under laboratory conditions for a first validation of the theoretical results. Therefore, a prototype model to test a lens fixation with a fluid bearing was developed and manufactured. The resulting deformations were measured with an interferometer and the effects are discussed.

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Beitrag (Sammelband oder Tagungsband)

ABC-polishing

Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach])

2018

ISBN: 978-1-5106-2270-8

DOI: 10.1117/12.2318549

Abstract anzeigen

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.