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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: Solution to the Shearing Problem
Author(s): C. Elster;I. Weingärtner
Journal: Applied Optics
Year: 1999
Volume: 38
Issue: 23
Pages: 5024
Optical Society of America
DOI: 10.1364/AO.38.005024
ISSN: 0003-6935
Web URL: http://www.osapublishing.org/viewmedia.cfm?uri=ao-38-23-5024&seq=0&html=true
Keywords: Interferometry,Optical inspection,Phase measurement
Tags: 8.42,Form
Abstract: Lateral shearing interferometry is a promising reference-free measurement technique for optical wave-front reconstruction. The wave front under study is coherently superposed by a laterally sheared copy of itself, and from the interferogram difference measurements of the wave front are obtained. From these difference measurements the wave front is then reconstructed. Recently, several new and efficient algorithms for evaluating lateral shearing interferograms have been suggested. So far, however, all evaluation methods are somewhat restricted, e.g., assume a priori knowledge of the wave front under study, or assume small shears, and so on. Here a new, to our knowledge, approach for the evaluation of lateral shearing interferograms is presented, which is based on an extension of the difference measurements. This so-called natural extension allows for reconstruction of that part of the underlying wave front whose information is contained in the given difference measurements. The method is not restricted to small shears and allows for high lateral resolution to be achieved. Since the method uses discrete Fourier analysis, the reconstructions can be efficiently calculated. Furthermore, it is shown that, by application of the method to the analysis of two shearing interferograms with suitably chosen shears, exact reconstruction of the underlying wave front at all evaluation points is obtained up to an arbitrary constant. The influence of noise on the results obtained by this reconstruction procedure is investigated in detail, and its stability is shown. Finally, applications to simulated measurements are presented. The results demonstrate high-quality reconstructions for single shearing interferograms and exact reconstructions for two shearing interferograms.

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