Mr. Nicolae Radu Doloca Profile

Nicolae Radu Doloca

Doctoral Student at Technische Univ Braunschweig

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Publications (3)

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Proceedings Article | 3 October 2008 Paper

Random-phase-shift Fizeau interferometer

Nicolae Radu Doloca, Rainer Tutsch

Proceedings Volume 7155, 71550S (2008) https://doi.org/10.1117/12.814528

KEYWORDS: Phase shifts, Interferometers, Photodiodes, Wavefronts, CCD image sensors, Sensors, Interferometry, Phase interferometry, Cameras, CCD cameras

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In the context of this article we demonstrate a novel Fizeau interferometric system that copes with the presence of vibrations. Besides the conventional high spatial, but low temporal resolution detector system (the CCD camera) used in phase shifting interferometry, an additional high temporal, but low spatial resolution detector system was integrated, in order to measure the random phase shifts that are induced under the influence of the vibrations. The additional sensor consists of three photodiodes. The acquired analog signals enable the measurement of the occurring phase shifts at three non-collinear locations on the test surface. Under the assumption of the rigid body shifts and tilts of the test object, the resulting phase shifts at the three individual locations enable the determination of the random phase shifts over the entire image aperture. While the random oscillations of the test object are continuously measured, the CCD camera acquires several interferograms. In consequence, a phase shifting algorithm for random phase shifts was applied. In order to prove the validity of the new interferometer, a test surface of known topography was measured. The results of the measurements in presence of vibrations show very good concordance with the surface data given by the supplier. The analysis of the root mean square (RMS) over ten different measurements shows a measurement repeatability of about 0.004 waves (approximately 2.5 nm for 632.8 nm laser wavelength).

Proceedings Article | 11 August 2008 Paper

Phase-shift Fizeau interferometer in presence of vibration

Radu Doloca, Hagen Broistedt, Rainer Tutsch

Proceedings Volume 7064, 706403 (2008) https://doi.org/10.1117/12.794031

KEYWORDS: Phase shifts, Photodiodes, CCD image sensors, Sensors, Semiconductor lasers, Interferometry, Interferometers, Wavefronts, CCD cameras, Camera shutters

Read Abstract +

In the context of this article we demonstrate a novel Fizeau interferometric system that copes with the presence of vibrations. Besides the conventional high spatial, but low temporal resolution detector system (the CCD camera) used in phase shifting interferometry, an additional high temporal, but low spatial resolution detector system was integrated, in order to measure the random phase shifts that are induced under the influence of the vibrations. The additional sensor consists of three photodiodes. The acquired analog signals enable the measurement of the occurring phase shifts at three non-collinear locations on the test surface. The resulting phase shifts at the three individual locations enable the determination of the random phase shifts over the entire image aperture. To avoid the smear phenomenon at very short exposure time, a beam shutter was integrated. Another alternative is to integrate a pulsed laser diode, for this purpose the concept of a wavelength meter is proposed. While the random oscillations of the test object are continuously measured, the CCD camera acquires several interferograms. In consequence, a phase shifting algorithm for random phase shifts was applied. In order to proof the validity of the new interferometer, a test surface of known topography was measured. The results of the measurements in presence of vibrations show very good concordance with the surface data given by the supplier. The analysis of the root mean square (RMS) over ten different measurement show a measurement repeatability of about 0.004 waves (approximately 2.5 nm for 632.8 nm laser wavelength).

Proceedings Article | 14 August 2006 Paper

Vibration induced phase-shift interferometer

Radu Doloca, Rainer Tutsch

Proceedings Volume 6292, 62920Y (2006) https://doi.org/10.1117/12.680857

KEYWORDS: Phase shifts, Photodiodes, Semiconductor lasers, Signal detection, Sensors, Pulsed laser operation, Optical fibers, Optical filters, Fringe analysis, CCD cameras

Read Abstract +

This paper presents the concept and the experimental setup of an interferometric system that is designed to work without vibration isolation and uses the random mechanical vibrations as phase shifter. An additional high temporal resolution detector system consisting of three photodiodes is used for the determination of the phase shifts that occur at the recording of the interference images. Two orthogonally polarized laser beams of different wavelengths, a continuous He-Ne laser and a pulsed laser diode, are coupled and expanded to the test and reference plates. To resolve the ambiguity problem of the profile orientation, additional information is obtained from the signals of two adjacent optical fibers placed in the He-Ne interference field. The laser beams are also split and expanded to a plate with tilted surfaces. The fringes that occur at the reflection on the surfaces are used to analyze the wavelength stability of the laser diode, taking the He-Ne wavelength as reference. An adequate PSI algorithm for random phase shifts is proposed.

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