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Philipp Froening

Bio: Philipp Froening is an academic researcher from University of Stuttgart. The author has contributed to research in topics: Holography & Digital holography. The author has an hindex of 3, co-authored 5 publications receiving 27 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, a flat metal plate is made to randomly vibrate when excited by a shaker, and a digital holographic interferometry out-of-plane optical system is used to investigate the temporal development of the induced transient deformations.
Abstract: A rectangular flat metal plate is made to randomly vibrate when excited by a shaker. A digital holographic interferometry out-of- plane optical system is used to investigate the temporal development of the induced transient deformations. The system relies on two and four laser pulses emitted within a single envelope of the flashlamp contained in the oscillator cavity of a ruby laser, and also on three CCD cameras used to record two or four digital images resulting from the same number of holographic interferograms. Hologram data reconstruction is per- formed digitally and Fourier evaluated to obtain quantitative deformation data for each of the formed interferograms. The deformation data is bro- ken down into resonant mode components, sums of which are used to computer reconstruct the experimental deformation data. The error pro- duced when using a finite sum of resonant mode components is consid- ered. Experimental and computer reconstruction results for the transient vibration deformation of the plate are presented and compared. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)01712-2)

13 citations

Proceedings ArticleDOI
29 Sep 1998
TL;DR: A ruby laser producing up to four pulses has been used and the optical phase of each hologram is obtained from the complex amplitude and the deformation between two laserpulses is calculated from phase subtraction and phase unwrapping of these two holograms.
Abstract: Pulsed digital holography is very useful for vibration analysis. In order to increase the temporal resolution a ruby laser producing up to four pulses has been used. The separate digital holograms (one hologram for each pulse) of an object under test are recorded in few microseconds on three CCD sensors. The images of the recorded holographic interference patterns are captured digitally with a framegrabber inside a Personal Computer. The reconstruction of the holograms is performed digitally by means of computer. For the later quantitative evaluation of the reconstructed holograms, the Fourier method is used. The optical phase of each hologram is obtained from the complex amplitude and the deformation between two laserpulses is calculated from phase subtraction and phase unwrapping of these two holograms. Experimental results are presented.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

5 citations

Proceedings ArticleDOI
01 Jun 1998
TL;DR: In this article, a series of the first 45 modeforms of a rectangular plate are measured and computed, and two separate digital holograms of the whole plate are recorded on a CCD sensor at each resonant frequency.
Abstract: Digital holographic interferometry has established as a readily available technique for measurement of surface deformations. In the method images containing the deformation of a surface as continuous function of high precision and fine resolution are obtained by computer subtraction of different holograms. On the other hand, the high precision finite elements method can be used to compute the deformation fields of elastic continua, where the resolution is similar to the resolution obtained with digital holographic interferometry. Combining both techniques, an attractive concept for testing is obtained: instead of performing FEM analysis in an isolated effort, it can be handled in parallel to the tests and preferably by the same personnel. This gives the opportunity for true interactive work, what may considerably ease the problem of harmonizing test and analysis. In order to demonstrate these features, a series of the first 45 modeforms of a rectangular plate are measured and computed. The plate is harmonically excited by a loudspeaker. Two separate digital holograms of the whole plate are recorded on a CCD sensor at each resonant frequency. Measured and computed modeforms are presented under identical format.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

5 citations

Proceedings ArticleDOI
09 Sep 1999
TL;DR: In this article, an optoelectronic system based on digital holography is used to measure the three dimensional vector components and object shape of a vibrating object, which are then combined into a 3D resultant deformation.
Abstract: An optoelectronic system based on digital holography is used to measure the three dimensional vector components and object shape of a vibrating object. Pulses from a ruby laser, with a separation in the range from 1 to 1000 microseconds, are used to record holograms on CCD sensors, which are later digitally reconstructed. Three different illumination directions are used to get the deformation along three different sensitivity vectors, that are afterwards combined into a 3D resultant deformation. To measure the shape of the object the two- wavelength method is used. The wavelength change is produced by changing the distance between the plates of the laser output etalon, thus obtaining the shape by subtracting the phases of the wavefronts recorded at those wavelengths. The data sets for the shape and 3D-deformation are combined and graphically shown. Finally, by using a non linear crystal (BBO) it was possible to double the frequency of the radiation emitted by the ruby laser allowing to get two wavelengths (694 nm and 347 nm) simultaneously and thus to record digital holograms with different sensitivities.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

2 citations

Proceedings ArticleDOI
01 Jun 1998
TL;DR: In this article, a rectangular metal plate is randomly excited by a shaker or by the impact of a small rod, and an optical measuring system for the evaluation of transient deformations is used.
Abstract: A rectangular metal plate is randomly excited by a shaker or by the impact of a small rod. To investigate the temporal development of the induced deformation, an optical measuring system for the evaluation of transient deformations is used. A ruby laser, which is able to produce four laser pulses within a few laser pulses within a few microseconds and a setup of three CCD-cameras for recording the four pulses/interferograms were used. The images of the recorded holographic interference patterns are captured digitally with a framegrabber inside a PC. The reconstruction of the holograms is performed also digitally in the computer. For the later is obtained from the complex amplitude and the deformation between two laser pulses is calculated from phase subtraction and phase unwrapping of these two holograms. Each deformation image can be decomposed into the eigenmodes of the plate, which have to be known/measured before. By measurement of four holograms with a known pulses separation one is able to determine the deformation states between each adjacent pulse and at least the temporal development of the deformation and contributing magnitude coefficients of the eigenmodes.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

2 citations


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Journal Article
TL;DR: In this article, a fast Fourier transform method of topography and interferometry is proposed to discriminate between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour generation techniques.
Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

3,742 citations

Journal ArticleDOI
TL;DR: In this article, proper orthogonal decomposition (POD) was applied to the modal vibration analysis of a metal plate, which was subject to vibrations with an electrodynamical shaker in a range of frequencies from 100 to 5000 Hz.
Abstract: The proper orthogonal decomposition (POD), also known as Karhunen–Loeve expansion, is applied to the modal vibration analysis of a metal plate. The metal plate was subject to vibrations with an electrodynamical shaker in a range of frequencies from 100 to 5000 Hz. The data were obtained from the measurements with a laser vibrometer. The plate vibration measurements were used to calculate the eigenfunctions and the eigenvalues. It was found that a large fraction of the total energy of the vibrations is contained within the first four POD modes. The essential features of the vibrations are thus described by only the first four eigenfunctions.

364 citations

Journal ArticleDOI
TL;DR: In this paper, an in-line digital holographic sensor (DHS) for monitoring and characterizing marine particulates is presented. Butler et al. used a small 10mW diode laser to project a collimated beam through the water column and onto a lensless CCD array.
Abstract: We report an in-line digital holographic sensor (DHS) for monitoring and characterizing marine particulates. This system images individual particles over a deep depth of field (>25 cm) with a resolution of 5 {mu}m. The DHS projects a collimated beam through the water column and onto a lensless CCD array. Some light is diffracted by particulates and forms an object beam; the undeflected remainder constitutes the reference beam. The two beams combine at the CCD array and create an in-line hologram, which is then numerically reconstructed. The DHS eliminates many problems traditionally associated with holography. The CCD recording material considerably lowers the exposure time and eliminates most vibration problems. The laser power needs are low; the DHS uses a small 10-mW diode laser. Rapid numerical reconstruction eliminates photographic processing and optical reconstruction. We successfully operated the DHS underwater on a remotely operated vehicle; our test results include tracing a single particle from one hologram to the next, thus deriving a velocity vector for marine mass transport. We outline our digital holographic reconstruction procedure, and present our graphical user interface and user software tools. The DHS is particularly useful for providing in situ ground-truth measurements for environmental remote sensing. (c) 2000 Societymore » of Photo-Optical Instrumentation Engineers.« less

101 citations

Journal ArticleDOI
TL;DR: In this method, the Laplacian of a detected hologram is used instead of the hologram itself for numerical reconstruction by computing the discrete Fresnel integral to significantly improve the image quality and give better resolution and higher accuracy of the reconstructed image.
Abstract: A simple method to suppress the zero-order diffraction in the reconstructed image of digital holography is presented. In this method, the Laplacian of a detected hologram is used instead of the hologram itself for numerical reconstruction by computing the discrete Fresnel integral. This method can significantly improve the image quality and give better resolution and higher accuracy of the reconstructed image. The main advantages of this method are its simplicity in experimental requirements and convenience in data processing.

40 citations

Journal ArticleDOI
TL;DR: In this paper, a twin oscillator, injection-seeded, pulsed Nd:YAG laser is incorporated into a pulsed TV holography set-up.

21 citations