Dr. Ralf D. Geckeler Profile

Dr. Ralf D. Geckeler

at Physikalisch-Technische Bundesanstalt

SPIE Involvement:

Author

Publications (29)

Proceedings Article | 3 October 2023 Presentation + Paper

Towards new generation long trace profiler LTP-2020: system design with different sensors in different operation modes

Valeriy Yashchuk, Kevan Anderson, Grant Cutler, Jeff Dickert, Damon English, Ralf Geckeler, Ian Lacey, Peter Takacs

Proceedings Volume 12695, 1269505 (2023) https://doi.org/10.1117/12.2677861

KEYWORDS: Sensors, Mirrors, Metrology, Diffraction gratings, Design and modelling, Autocollimators, X-ray optics, Mirror surfaces, X-rays, Optical surfaces

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Proceedings Article | 2 October 2019 Presentation + Paper

Transfer of autocollimator calibration for use with scanning gantry profilometers for accurate determination of surface slope and curvature of state-of-the-art x-ray mirrors

Ian Lacey, Kevan Anderson, Jeff Dickert, Ralf Geckeler, Andreas Just, Frank Siewert, Brian Smith, Valeriy Yashchuk

Proceedings Volume 11109, 1110905 (2019) https://doi.org/10.1117/12.2529519

KEYWORDS: Calibration, Mirrors, Autocollimators, Error analysis, X-ray optics, Precision calibration, X-rays, Profilometers, Metrology, Sensors

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Proceedings Article | 9 September 2019 Paper

A precise aperture centring device (ACenD) for autocollimator-based surface measuring profilers

Bernd Grubert, David Kreitschik, Olaf Schnabel, Frank Siewert, Ralf Geckeler, Matthias Schumann, Andreas Just, Michael Krause, Tanfer Yandayan, S. Asli Akgoz

Proceedings Volume 11109, 1110902 (2019) https://doi.org/10.1117/12.2531613

KEYWORDS: Calibration, Autocollimators, Distance measurement, Charge-coupled devices, Reticles, CCD cameras, Objectives, Metrology, Mirrors, Beam splitters

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Proceedings Article | 9 September 2019 Paper

High-accuracy autocollimator calibration by interferometric 2D angle generator

V. Heikkinen, V. Byman, M. Shpak, R. Geckeler, A. Just, M. Krause, M. Schumann, A. Lassila

Proceedings Volume 11109, 1110903 (2019) https://doi.org/10.1117/12.2531023

KEYWORDS: Autocollimators, Calibration, Interferometers, Reflectors, Interferometry, Mirrors, Sensors, Metrology

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Proceedings Article | 17 September 2018 Presentation + Paper

The ALS OSMS: Optical Surface Measuring System for high accuracy two-dimensional slope metrology with state-of-the-art x-ray mirrors

Ian Lacey, Kevan Anderson, Gary Centers, Ralf Geckeler, Gevork Gevorkyan, John Grossiord, Andreas Just, Theo Nicolot, Brian Smith, Valeriy Yashchuk

Proceedings Volume 10760, 1076002 (2018) https://doi.org/10.1117/12.2321347

KEYWORDS: Mirrors, Calibration, Metrology, X-ray optics, X-rays, Autocollimators, Gaussian filters, Sensors

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Proceedings Article | 7 September 2017 Presentation + Paper

A new ultra-high-accuracy angle generator: current status and future direction

Christian Guertin, Ralf Geckeler

Proceedings Volume 10385, 103850A (2017) https://doi.org/10.1117/12.2274143

KEYWORDS: Calibration, Metrology, Mirrors, Prototyping, Autocollimators, Optical encoders, Positioning equipment, Position sensors, Precision calibration

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Proceedings Article | 5 September 2014 Paper

Pushing the limits: latest developments in angle metrology for the inspection of ultra-precise synchrotron optics

Tanfer Yandayan, Ralf Geckeler, Frank Siewert

Proceedings Volume 9206, 92060F (2014) https://doi.org/10.1117/12.2060953

KEYWORDS: Autocollimators, Calibration, Metrology, Computer programming, Mirrors, Inspection, Synchrotrons, Head, Optical testing, Optics manufacturing

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Proceedings Article | 13 May 2013 Paper

Modelling PTB's spatial angle autocollimator calibrator

Oliver Kranz, Ralf Geckeler, Andreas Just, Michael Krause

Proceedings Volume 8789, 87890D (2013) https://doi.org/10.1117/12.2020279

KEYWORDS: Autocollimators, Calibration, Reflectors, Profilometers, Optical testing, Reflection, Modeling, Metrology, Mathematical modeling, Manufacturing

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SPIE Journal Paper | 1 July 2011

Optimal alignment of mirror-based pentaprisms for scanning deflectometric devices

Samuel Barber, Valeriy Yashchuk, Ralf Geckeler, Mikhail Gubarev, Jana Buchheim, Frank Siewert, Thomas Zeschke

OE, Vol. 50, Issue 07, 073602, (July 2011) https://doi.org/10.1117/12.10.1117/1.3598325

KEYWORDS: Mirrors, Autocollimators, Optical alignment, Alignment procedures, Error analysis, Ray tracing, Optical engineering, Light sources, Reliability, Computer simulations

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SPIE Journal Paper | 1 May 2011

Developmental long-trace profiler using optimally aligned mirror-based pentaprism

Samuel Barber, Gregory Morrison, Valeriy Yashchuk, Mikhail Gubarev, Ralf Geckeler, Jana Buchheim, Frank Siewert, Thomas Zeschke

OE, Vol. 50, Issue 05, 053601, (May 2011) https://doi.org/10.1117/12.10.1117/1.3572113

KEYWORDS: Mirrors, Autocollimators, Alignment procedures, Optical alignment, Kinematics, Optical engineering, Spherical lenses, Error analysis, Light sources, Calibration

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Proceedings Article | 2 September 2010 Paper

Developmental long trace profiler using optimally aligned mirror-based pentaprism

Samuel Barber, Gregory Morrison, Valeriy Yashchuk, Mikhail Gubarev, Ralf Geckeler, Jana Buchheim, Frank Siewert, Thomas Zeschke

Proceedings Volume 7801, 780103 (2010) https://doi.org/10.1117/12.859925

KEYWORDS: Mirrors, Autocollimators, Alignment procedures, Optical alignment, Ray tracing, Kinematics, Error analysis, Calibration, Spherical lenses, X-ray optics

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Proceedings Article | 12 January 2009 Paper

Interferometry at the PTB Nanometer Comparator: design, status and development

J. Flügge, Ch. Weichert, H. Hu, R. Köning, H. Bosse, A. Wiegmann, M. Schulz, C. Elster, R. Geckeler

Proceedings Volume 7133, 713346 (2009) https://doi.org/10.1117/12.821252

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Proceedings Article | 17 October 2008 Paper

Development of a 1.5D reference comparator for position and straightness metrology on photomasks

J. Flügge, R. Köning, Ch. Weichert, W. Häßler-Grohne, R. Geckeler, A. Wiegmann, M. Schulz, C. Elster, H. Bosse

Proceedings Volume 7122, 71222Y (2008) https://doi.org/10.1117/12.801251

KEYWORDS: Interferometers, Photomasks, Metrology, Mirrors, Computer programming, Calibration, Sensors, Microscopes, Beam splitters, Image registration

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Proceedings Article | 3 September 2008 Paper

Distance-dependent influences on angle metrology with autocollimators in deflectometry

Ralf Geckeler, Andreas Just

Proceedings Volume 7077, 70770B (2008) https://doi.org/10.1117/12.793742

KEYWORDS: Autocollimators, Calibration, Metrology, Reticles, Charge-coupled devices, Objectives, Optical components, Sensors, Spherical lenses, Mirrors

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Proceedings Article | 20 September 2007 Paper

Optimized use and calibration of autocollimators in deflectometry

Ralf Geckeler, Andreas Just

Proceedings Volume 6704, 670407 (2007) https://doi.org/10.1117/12.732384

KEYWORDS: Autocollimators, Calibration, Deflectometry, Metrology, Objectives, Mirrors, Head, Charge-coupled devices, Optical components, Standards development

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Proceedings Article | 20 September 2007 Paper

Proposal for a universal test mirror for characterization of slope measuring instruments

Valeriy Yashchuk, Wayne McKinney, Tony Warwick, Tino Noll, Frank Siewert, Thomas Zeschke, Ralf Geckeler

Proceedings Volume 6704, 67040A (2007) https://doi.org/10.1117/12.732719

KEYWORDS: Calibration, Mirrors, Nano opto mechanical systems, Autocollimators, Optical components, Light sources, Free electron lasers, Metrology, Precision calibration, X-ray optics

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Proceedings Article | 18 June 2007 Paper

Stability analysis for the TMS method: Influence of high spatial frequencies

Axel Wiegmann, Clemens Elster, Ralf Geckeler, Michael Schulz

Proceedings Volume 6616, 661618 (2007) https://doi.org/10.1117/12.726116

KEYWORDS: Sensors, Interferometers, Distortion, Spatial frequencies, Computer simulations, Optical scanning systems, Interferometry, Distance measurement, Autocollimators, Wavefronts

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The Traceable Multi Sensor (TMS) system is a scanning system for the measurement of the topography of large optical surfaces. The system uses a compact interferometer with an aperture of some millimetres to realize multiple distance sensors and an autocollimator for the angle measurement. In contrast to common stitching techniques, the systematic sensor errors are calculated in addition to the entire topography by the TMS algorithm. Additionally, piston and tilt at each position of the interferometer are determined by the algorithm. An essential requirement for the algorithm is the exact lateral positioning of the sensor at given locations. The goal of this paper is to investigate the influence of a class of error sources on the resulting topography estimation using computer simulations. The errors of this class result in inexact measurement positions of the distance sensors. Especially the lateral positioning errors of the scanning stage lead to increasing errors for short wavelengths. For topography wavelengths below 3mm with an amplitude of 100nm the resulting topography error increases to 3nm and more. For longer wavelengths the positioning errors are no longer the dominant error source and the root mean square error of the resulting topography is approximately 1 nm for positioning errors with a standard deviation of 5 &mgr;m. The pixel distance error and distortion of the interferometer strongly influence the topography measurement of specimens with large deviations from a plane. The simulations show that for a topography with a peak to valley of 50 &mgr;m the root mean square error of the reconstructed topography is below 10 nm. Furthermore, a possibility to compensate the lateral positioning error of the scanning stage is presented which makes the TMS method nearly independent of positioning errors of the scanning stage. As a consequence, it is possible to use systems of non equidistant distance sensors whose lateral distances are independent of the positioning interval.

Proceedings Article | 11 September 2006 Paper

ESAD shearing deflectometry: potentials for synchrotron beamline metrology

Ralf Geckeler

Proceedings Volume 6317, 63171H (2006) https://doi.org/10.1117/12.716301

KEYWORDS: Autocollimators, Deflectometry, Calibration, Measurement devices, Prisms, Metrology, Interferometry, Synchrotrons, Nano opto mechanical systems, Zerodur

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Proceedings Article | 14 August 2006 Paper

Error minimization in high-accuracy scanning deflectometry

Ralf Geckeler

Proceedings Volume 6293, 62930O (2006) https://doi.org/10.1117/12.679339

KEYWORDS: Prisms, Autocollimators, Interferometry, Mercury, Deflectometry, Mirrors, Calibration, Solids, Measurement devices, Interferometers

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Proceedings Article | 15 September 2005 Paper

Scanning form measurement for curved surfaces

Michael Schulz, Ralf Geckeler

Proceedings Volume 5921, 592106 (2005) https://doi.org/10.1117/12.614790

KEYWORDS: Sensors, Interferometers, Autocollimators, CCD image sensors, Calibration, Charge-coupled devices, Mirrors, Distance measurement, Spherical lenses, Image resolution

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Proceedings Article | 31 August 2005 Paper

Traceable multiple sensor system for absolute form measurement

Michael Schulz, Joachim Gerhardt, Ralf Geckeler, Clemens Elster

Proceedings Volume 5878, 58780A (2005) https://doi.org/10.1117/12.614726

KEYWORDS: Sensors, Autocollimators, Interferometers, Calibration, CCD image sensors, Distance measurement, Charge-coupled devices, Sensor calibration, Imaging systems, Spatial resolution

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Proceedings Article | 13 June 2005 Paper

High-accuracy profile form measurement by a scanning system consisting of an angle sensor and coupled distance sensors

Joachim Gerhardt, Ralf Geckeler, Michael Schulz, Clemens Elster

Proceedings Volume 5856, (2005) https://doi.org/10.1117/12.612492

KEYWORDS: Sensors, Distance measurement, Interferometers, Error analysis, Autocollimators, Calibration, Optical scanning systems, CCD image sensors, Optical testing, Mathematical modeling

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Proceedings Article | 10 September 2004 Paper

A new method and a novel facility for ultra precise 2D topography measurement of large optical surfaces

Matthias Wurm, Ralf Geckeler

Proceedings Volume 5457, (2004) https://doi.org/10.1117/12.545646

KEYWORDS: Autocollimators, Charge-coupled devices, Calibration, Sensors, Reticles, Optical testing, Algorithm development, Monochromatic aberrations, Deflectometry, Reconstruction algorithms

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Proceedings Article | 20 November 2003 Paper

High-accuracy form measurement of large optical surfaces

Michael Schulz, Ralf Geckeler, Jens Illemann

Proceedings Volume 5190, (2003) https://doi.org/10.1117/12.503700

KEYWORDS: Calibration, Sensors, Autocollimators, Interferometers, Prisms, Zerodur, Optical testing, Deflectometry, Spherical lenses, Time metrology

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Proceedings Article | 24 December 2002 Paper

Topography measurement of nanometer synchrotron optics

Jens Illemann, Ralf Geckeler, Ingolf Weingartner, Carsten Schlewitt, Bernd Grubert, Olaf Schnabel

Proceedings Volume 4782, (2002) https://doi.org/10.1117/12.450982

KEYWORDS: Calibration, Head, Autocollimators, Prisms, Zerodur, Mirrors, Optical testing, Synchrotrons, Synchrotron radiation, Optical components

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Proceedings Article | 11 November 2002 Paper

Sub-nm topography measurement by deflectometry: flatness standard and wafer nanotopography

Ralf Geckeler, Ingolf Weingaertner

Proceedings Volume 4779, (2002) https://doi.org/10.1117/12.451723

KEYWORDS: Autocollimators, Calibration, Deflectometry, Error analysis, Prisms, Zerodur, Semiconducting wafers, Reconstruction algorithms, Measurement devices, Algorithm development

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Proceedings Article | 11 November 2002 Paper

Novel concept for the ultraprecise and fast measurement of the nanotopography of large wafers

Ingolf Weingaertner, Matthias Wurm, Ralf Geckeler, Clemens Elster, Michael Schulz, Eugen Dumitrescu, Stefan Krey, Josef Heinisch

Proceedings Volume 4779, (2002) https://doi.org/10.1117/12.451713

KEYWORDS: Semiconducting wafers, Measurement devices, Spatial frequencies, Distance measurement, Interferometers, Reconstruction algorithms, Algorithm development, Sensors, Wafer-level optics, Deflectometry

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The measurement of the topography or the nanotopography of large wafers up to 450 mm in diameter with satisfactory lateral resolution and nanometer uncertainty is still an unsolved problem. The topography of wafers covers a relatively large measurement range as wafers have surfaces with a so-called "slightly unflat" topography which mostly exceeds the measurement capabilities of interferometers. For the ultraprecise and traceable measurement of the slope and topography of slightly unflat optical surfaces, a novel scanning deflectometry principle has been developed. An uncertainty of the topography in the nanometer range will be achieved, as this principle minimizes error influences and allows a highly precise calibration of the angle measuring device. The main goal is to use this principle for the ultraprecise measurement of the nanotopography of large wafers. The measurement principle is based on the analysis of differences of reflection angles obtained at surface points which are separated by large lateral shears. It does not rely on external reference surfaces of matched topography and in first and second order is independent of any stage errors and the whole-body motion of the specimen. The measurands are directly traced back to the base units of angle and length. The specific idea of wafer measurement is to combine rotational and linear scanning with the measurement of slope difference vectors and to arrive at an unambiguous solution for the topography and nanotopography. The equations with the slope difference vectors are solved to reconstruct the slope vectors, as newly developed mathematical algorithms allow the surface slope to be reconstructed from slope differences for two different shears. This is reached by applying natural extensions and shearing transfer functions by a mathematically exact method over the whole surface area. Further the differential equations for the slope vectors are solved to unambiguously reconstruct the topography. With this method it is possible to achieve nanometer uncertainty and at the same time a high lateral resolution, short measurement times and the possibility of mastering the large measurement range necessary for slightly unflat wafer surfaces.

Proceedings Article | 22 October 2001 Paper

Use and treaceable calibration of autocollimators for ultra-precise measurement of slope and topography

Ralf Geckeler, Ingolf Weingaertner, Andreas Just, Reinhard Probst

Proceedings Volume 4401, (2001) https://doi.org/10.1117/12.445620

KEYWORDS: Autocollimators, Calibration, Head, Mirrors, Error analysis, Charge-coupled devices, Algorithm development, Reconstruction algorithms, Temperature metrology, Reflection

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Recently, a novel scanning principle (ESAD - Extended Shear Angle Difference) has been presented for the ultra-precise determination of slope and topography of near-plane surfaces which is based on the measurement of differences of reflection angles with an autocollimator. It uses large lateral displacements (shears) of the order of mm to cm, and a newly developed algorithm allows the exact reconstruction of the slope from the angle differences with two different shears. The topography is then derived from the slope by an accurate integration procedure. Reproducibility of the reconstructed topography of the order of below 1 nm for scans over a near-flat surface has already been achieved. In contrast to interferometric techniques, this scanning method does not rely on an external reference surface of matched topography. The measurands are directly traced back to the base units of angle and length. Therefore, this technique is well suited for creating a very precise standard for straightness and flatness. A central element considerably influencing the overall uncertainty is the autocollimator itself, making a high-accuracy traceable calibration of the device necessary. Autocollimators are calibrated at the PTB by the use of a primary standard angle comparator which is traced back to the natural standard of the full angle of 2Pi rad. The traceable calibration is realized by an incremental circular scale, incorporated into a highly precise rotary table as a measuring system, consisting of a radial optical phase grating and several photoelectric reading heads, thus reaching an angular resolution of approximately 0.001 arcsec. With this comparator, calibration of an electronic autocollimator with 0.001 arcsec resolution and a measurement range of (150 arcsec with an uncertainty of 0.007 arcsec has currently been achieved. The autocollimator type to be used in the ESAD scanning facility was calibrated and investigated with respect to its resolution, reproducibility and accuracy in the range of 0.01 arcsec over a variety of measurement ranges. These experiences will be described. Methods to avoid or control error influences are discussed.

Proceedings Article | 22 October 2001 Paper

Tracing back radius of curvature and topography to the base unit of length with ultraprecision

Ingolf Weingaertner, Michael Schulz, Ralf Geckeler, Otto Jusko, Michael Neugebauer, Arnold Nicolaus, Gerhard Boensch

Proceedings Volume 4401, (2001) https://doi.org/10.1117/12.445618

KEYWORDS: Optical spheres, Calibration, Sensors, Aspheric lenses, Interferometers, Spherical lenses, Wavefronts, Sensor calibration, Mirrors, Manufacturing

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