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Virtual experiments

Working group 8.42


In a virtual experiment a measurement process is modeled mathematically and simulated on a computer. The employed mathematical model of the physical experiment is sought to be as realistic as possible. Virtual experiments allow different scenarios to be easily explored. In this way, measurement processes can be designed and specified with the help of the computer. Virtual experiments can be used to estimate the accuracy that is reached by a real measurement device. Dominant sources of uncertainty can be identified and quantitatively explored by carrying out a sensitivity analysis of the virtual experiment. The results obtained can be used to optimize the considered measurement system. Virtual experiments can help in the development of procedures from data analysis for real experiments, for example to assess and compare different estimation procedures under realistic conditions, or to validate assumptions made about the distribution of measured data.

Simulation of a tilted-wave interferometer (left) and a virtual 3D-measurement of an optical surface (right) using SimOptDevice.


The research of PTB’s Working Group 8.42 focuses on virtual experiments for optical measurement devices and the development of procedures from data analysis for evaluating corresponding measurements. To this end, the simulation environment SimOptDevice has been developed as a software library, which is successfully employed in many applications regarding length-/form- and coordinate measurements, as well as photometry. SimOptDevice is regularly maintained and its functionality improved. It is currently applied to the tilted-wave interferometer, which is suitable for the optical form measurement of aspheres and freeforms. Methods of data analysis in conjunction with virtual experiments are developed and applied to solve the involved inverse problem and to calibrate the measurement process. Other research topics include the evaluation of uncertainties associated with real measurements utilizing the results of the corresponding virtual experiment, or the use of methods from deep learning in connection with virtual experiments. For example, virtual experiments can be used to create a database needed to train a neural network that is designed for analyzing experimental data.


Publication single view


Title: Concept, design and capability analysis of the new Deflectometric Flatness Reference at PTB
Author(s): M. Schulz, G. Ehret, M. Stavridis;C. Elster
Journal: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Year: 2010
Volume: 616
Issue: 2-3
Pages: 134--139
DOI: 10.1016/j.nima.2009.10.108
ISSN: 01689002
Web URL: http://www.sciencedirect.com/science/article/pii/S0168900209020592
Keywords: ESAD,Flatness measurement,Nanometrology,Simulation
Tags: 8.42,Deflectometry,Form,SimOpt
Abstract: At PTB, a new setup for the highly accurate topography measurement of nearly flat optical surfaces is now under construction. The so-called Deflectometric Flatness Reference (DFR) is designed to measure in the direct deflectometric mode by applying an autocollimator and a scanning pentaprism, and in the difference deflectometric mode corresponding to the Extended Shear Angle Difference (ESAD) principle invented by PTB. With the new DFR instrument, horizontally as well as vertically orientated specimens with dimensions of up to 1m and a mass of up to 120kg will be measurable. The design of the new instrument is supported by employing a comprehensive simulation environment developed for dimensional measuring machines. The mechanical and optical concept is illustrated together with the current design of the DFR setup. Results from the simulations are presented to derive requirements for tolerated mechanical stage deviations and alignment accuracies.

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