Speckle interferometry with CO2 laser (10 micrometers) and microbolometer array has been developed and the final
outcome is a mobile interferometer. The long wavelength allows to measure large deformations and is well immune
against external perturbations, so as it can be used in field conditions. The technique is based on specklegram recording
on the microbolometer array. The background of the specklegram is constituted by the thermal image of the object.
Consequently the technique allows simultaneous observation of deformation and temperature difference when an object
undergoes a given stress. We show several applications in aerospace nondestructive testing.
The availability of high resolution CCD and CMOS sensors together with the increasing computer capacity have enabled the development of different interferometrical techniques (speckle interferometry, digital holography, digital sherography) which are well suited for real time measurements. Two or more interferograms are recorded on a digital sensor at different times and the deformation of the object occurring between the exposures is calculated from the phase change. Since the process to investigate can be very fast we cannot use the well-known temporal phase shift method for the determination of the phase but we use a spatial carrier method which allows to determine that phase from one single hologram. We will show that this method can be used as well for shearography. Applications of digital holographic techniques for the investigation of vibrations, defect detection in mechanical structure and time resolved measurement of deformation of microelectromechanical systems (MEMS) are presented together with some investigation of mechanical structures by using digital shearography with spatial carrier.
For the society it is of great interest to make cultural heritage accessible to the general public. The subsequent increase of museum loan services increases the risk of accelerated degeneration. Hence, in addition to the age related deterioration, transportation can be another source of damage. Despite modern packaging technologies, vibrations and environmental climate change can add up and damage the transported object. Besides obvious mechanical influencing quantities, a main concern is the detection of climate induced damages. Changes in the relative humidity cause inner strain, which may lead to defect formations and damages. White light fringe projection was applied to detect object changes due to variations of the relative humidity. First measurements
indicated a sensitivity down to a relative humidity change of 6 %. Recently, the Stuppach Madonna, a painting
by Matthias Grunewald (painted 1514 - 1516), was investigated with shearography after the return from an exhibition. The obtained shearograms revealed a variety of defects like bubbles, delaminations and tunnels caused by wood worms. Even the planking of the wooden panel and existing putty could be detected.
This paper describes the first steps of a project with the aim of investigating and implementing a method to detect and classify transport related damages on works of art.
We present the development of a speckle interferometer based on a CO 2 laser and using a thermal infrared camera based on an uncooled microbolometer array. It is intended to be used for monitoring deformations as well as detecting flaws in aeronautical composites, with a smaller sensitivity to displacement compared to an equivalent system using visible (VIS) lasers. Moreover the long wavelength allows working with such interferometers outside the laboratory. A mobile system has been developed on the basis of previous laboratory developments. Then it is validated in a variety of industrial nondestructive testing applications in field working conditions.
In this paper we present extension of electronic speckle pattern interferometry (ESPI) to the long wave infrared range
which makes use of CO2 lasers and digital recording on microbolometer based uncooled thermographic cameras. The
measurement range and accuracy of this technique is related to the wavelength of the laser. In visible light ESPI is often
not well suited for field applications or for large displacement measurement due to the short wavelength used, which
imposes high stability constraints. With wavelengths around 10 micrometers, corresponding to CO2 lasers, we have a
typical 20 factor of decrease of the stability requirements; meantime the range of measurement is increased by the same
factor. We will show some important steps for the development of the system and we will give some interesting results
obtained in industrial non-destructive testing applications.
Testing with a single holographic lens or grating in a collimated beam is normally not possible because of the inherent tilt caused in the wavefront. The tilt between the two beams in shearing creates a large number of linear fringes which overshadow the information about the wavefront. However, here, we show that we can use this tilt to make quantitative measurements which was otherwise not possible. In the novel method, we obtain shear in a relatively simple way, and at the same time we extract phase information using spatial Fourier transform technique. This technique is suitable for making quantitative measurement of wavefront and disturbances in turbulent conditions. Here, we demonstrated the real-time phase measurement capacity of the interferometer, a result of one such application is shown.
In this paper, we demonstrate how short coherence digital holography with a pulsed fiber laser frequency comb may be
used for multi-level optical sectioning. For the proof of the principle, a conic object having a size of few centimeters is
used. The object shape is obtained by digitally reconstructing and processing a sequence of holograms recorded during
stepwise shifting of a spherical mirror in the reference arm of the holographic set-up. First experimental results are
presented.
Optical techniques are well suited for the measurement of microcomponents but give accurate results only when calibrated systems are used. We present a strategy for the calibration of setups to be used for the measurements of microsystems. We develop, at first, standard reference devices whose out-of-plane and in-plane displacements are precisely reproducible when submitted to standard loadings. These reference devices have been manufactured and tested by optical techniques and may be used for the calibration of optical measuring systems. Furthermore, a detailed discussion of the measurement uncertainty, according to the ISO's "Guide of Expression of Uncertainty in Measurement," is given.
Advances in information technology open up the potential of combining optical systems with net based infrastructures,
allowing for remote inspection and virtual metrology. In this paper, we report our recent work on
building a remote laboratory for digital holographic metrology. We describe the architecture and the techniques
involved in setting up the remote controlling metrology system. Further consideration will be given to the integration
into an advanced infrastructure for remote experimentation, data storage and publication. Some other
important issues such as information security will not be addressed.
The applying of stroboscopic methods in optical holographic measurements is limited due to the influence of quality of holographic arrangement on the accuracy of results. Parasitical interferometric fringes as a result of pulse duration or phase synchronization instability may be presented on a hologram and, such fringes have no relationship to real displacement or deformation. It creates a lot of troubles for researchers and, finally leads to refuse of using the stroboscopic technique. However, the troubles may be successfully overcome as if we analyze all kinds of influences on the quality of stroboscopic interferogram. This paper reports about the influence of pulse duration and phase instability. The presented results allow to realize correct stroboscopic holographic measurement. The problem of quality of applied arrangement has been discussed as well.
Theoretical and experimental aspects of frequency-bounded vibration investigations were discussed. It was shown that stroboscopic holography has an advantage in comparison with other ones. Digital calculation shows that the result depends on accuracy of setting the phases of strobe pulses.
Victor Vorobyev, Nataly Soboleva, Oleg Vitrik, Yana Vitrik, Michel Guserv, Murat Bukayev, Igor Alexeenko, Elena Kuzmina, Alexander Malov, Serge Antonyuk, Yury Vigovsky, Vasily Levit, Nataly Qutyakova, Sergey Malov
The results of the mathematical calculations for the tooth bridge prostheses are discussed. Holographic interferometry with double exposition is used for verification of the model calculation results. This method may be used to define the safety degree and the quality of the implant and besides, the dentures influence on the bone tissue. There were given the results of the experimental work on different kinds of implants and the way they can be inserted into the jaw.
Theoretical and experimental aspects of frequency-bounded vibration investigations were observed. It was shown, that stroboscopic holography has an advantage in comparison with other ones. Digital calculation shows that the result depends on accuracy of setting the phases of stobe pulses. Thus, it is necessary to apply very precise driver for the creation of laser pulses in needed phases. Experimetnal set-up for stroboscopic holographic investigation of obunded vibration by using continue-wave laser was described. Experimental investigations have shown that stroboscopic technique allows to separate different mode-shapes vibrating simultaneously. Pulse laser and digital holographic technique was applied to frequency-bounded vibrational investigations as well. The results of digital evaluations of separated mode-shapes were presented.
Victor Vorobyev, Oleg Vitrik, Mikhail Gusev, Murat Bukayev, Alexander Malov, Igor Alexeenko, Elena Kuzmina, Nataly Soboleva, Yana Vitrik, Yury Vigovsky, Vasily Levit, Nataly Qutyakova, Sergey Malov, Serge Antonyuk
The results of the mathematical calculations for the tooth bridge prostheses are discussed. Holographic interferometry with double exposition is used for verification of the model calculation results.
A system based on digital holographic interferometry in combination with a rigid and a flexible endoscope is described. A Q-switched pulsed laser is used. Two digital holograms of the test object, corresponding to the two laser pulses, are captured at separate video frames of the CCD-camera, transferred in a frame grabber and further processed in a PC. If during the interval between the two laser pulses (usually in the range of 5-600 ?s) the object undergoes a vibration, a fringe pattern will result from the difference between the two holograms. This fringe pattern has the information needed to quantitatively evaluate the vibration. Two compact systems (using rigid and flexible endoscopes) have been developed to be used for many applications, both mechanical and biological, where measurements need to be performed at "hidden" surfaces or inside more or less closed objects. The quality of the results obtained by using mechanical objects is usually better, this can be easily explained by the fact that a biological surface is much more complex, in particular some parts reflects well the light and some other absorb it. Experimental results are presented.
A system based on digital holographic interferometry in combination with an endoscope is described. A Q-switched pulsed laser is used. Two digital holograms of the test object, corresponding to the two laser pulse, are captured at separate video frames of the CCD-camera, transferred in a frame grabber and further processed in a PC. If during the interval between the two laser pulses the object undergoes a deformation, a fringe pattern will result from the difference between the two holograms. This fringe pattern has the information needed to quantitatively evaluate the amount of the deformation. A compact system has been developed to be used for many applications, both mechanical and biological, where measurements need to be performed at 'hidden' surfaces or inside more or less closed objects. The quality of the result obtained by using mechanical objects is usually better, this can be easily explained by the fact that a biological surface is much more complex, in particular some parts reflect well the light and some other absorb it. A comparison of different endoscopes as object image carrier in pulsed digital holography is presented.
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