Mobile speckle interferometer in the long-wave infrared for aeronautical nondestructive testing in field conditions

in Optical Engineering : The Journal of the Society of Photo-Optical Instrumentation Engineers (2013), 52(10),

Abstract We present the development of a speckle interferometer based on CO2 laser and using a thermal infrared camera based on uncooled microbolometer array. It is intended to be used for monitoring ... [more ▼]

Abstract We present the development of a speckle interferometer based on CO2 laser and using a thermal infrared camera based on uncooled microbolometer array. It is intended to be used for monitoring deformations as well as flaw detection in aeronautical composites, with a smaller sensitivity to displacement compared to equivalent system using visible lasers. Moreover the long wavelength allows working with such interferometer under out-of-laboratory conditions. 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 under field working conditions. [less ▲]

Digital holographic interferometry with CO2 lasers and diffuse illumination applied to large space reflectors metrology

in Applied Optics (2013), 52(1), 102-116

Digital holographic interferometry in the long wave infrared domain has been developed by combining a CO2 laser and a microbolometer array. The long wavelength allows large deformation measurements which ... [more ▼]

Digital holographic interferometry in the long wave infrared domain has been developed by combining a CO2 laser and a microbolometer array. The long wavelength allows large deformation measurements which are of interest in the case of large space reflectors undergoing thermal changes when in orbit. We review holography at such wavelengths and present some specific aspects related to this spectral range on our measurements. For the design of our digital holographic interferometer we studied the possibility of illuminating specular objects by a reflective diffuser. We discuss the development of the interferometer and the results obtained on a representative space reflector, first in the laboratory and then during vacuum cryogenic test. [less ▲]

Long-wave infrared digital holography for the qualification of large space reflectors

Conference (2012, October 09)

Deformation metrology of complex and large space reflectors is a recurrent problem addressed by ESA. The challenging tasks of on-ground qualification and verification testing are to achieve the required ... [more ▼]

Deformation metrology of complex and large space reflectors is a recurrent problem addressed by ESA. The challenging tasks of on-ground qualification and verification testing are to achieve the required accuracy in the measurement of these reflectors deformation and to verify their performance under simulated space conditions (vacuum, low temperature). A long-wave infrared digital holographic interferometer for the verification and validation of this type of reflector in a space environment is presented. It has been developed to fill the gap between holography/interferometry techniques in the visible wavelengths and methods based on structured light illumination like videogrammetry, stereocorrelation, and fringe/pattern projection. The former provide a good measurement uncertainty but the displacements are often too large to be measured and they require a very stable environment, while the latter provide large measurement range but with higher measurement uncertainty. The new instrument is based on digital holography and uses a CO2 lasers emitting at 10.6 µm combined with a commercial thermographic camera. A diffuser is illuminated by the laser beam, producing a speckle wavefront which is observed after reflection on the reflector surface. This reflected speckle wavefront behaves exactly as if the reflector was a diffusive surface, producing its own speckle, allowing the measurement of its deformation. The advantage of this configuration compared to a classical interferometer working at 10.6 µm, is that it requires no specific optics such as a null lens (in the case of parabola) or expensive illumination/collection optics (in the case of ellipse). The metrological certification of the system was performed in the laboratory by measuring the tilts of a 1.1 meter diameter parabolic reflector. The displacements are measured in parallel with a Doppler effect interferometer and the measurement uncertainty is estimated. The application of the new interferometer to the measurement of an elliptic reflector is also presented. The technique has been certified during a thermal-vacuum test. The deformation of the parabolic reflector is measured for a temperature variation from 288 K down to 113 K. The results are compared to previous results obtained on the same reflector with a high spatial resolution infrared interferometer, also developed at CSL. [less ▲]

Digital Holographic Interferometry and ESPI at Long Infrared Wavelengths with CO2 Laser (invited paper)

in Digital Holography and 3D Imaging (DH2012) (2012, April 28)

Holographie digitale en infrarouge lointain en vue de la mesure de déformation de grands réflecteurs spatiaux en ambiance vide-thermique

Conference (2011, November 23)

Development of digital holography in the long wave infrared range for assessment of space reflectors

in Proceedings of ICSO 2010 - International Conference on Space Optics (2010, October)

Electronic speckle pattern interferometry in Long Wave Infrared: a new technique for combining temperature and displacement measurements. Applications in thermo-mechanical assessment of structures

in Proceedings of ICSO 2010 - International Conference on Space Optics (2010, October)

Étude et développement de techniques de métrologie de déplacements en lumière cohérente en infrarouge thermique

Doctoral thesis (2010)

This thesis presents the works realised to apply ESPI and digital holography techniques at 10 µm for the monitoring of surface displacements of aerospace structures and space re- flectors. We consider ... [more ▼]

This thesis presents the works realised to apply ESPI and digital holography techniques at 10 µm for the monitoring of surface displacements of aerospace structures and space re- flectors. We consider objects with dimensions from a few tens of centimetres to more than one metre and with measurement ranges extending from a few micrometers to hundreds of micrometers. For specular surfaces where no diffusive coatings are allowed, we present the speckle pro- jection technique. We implement it in the special case of space reflectors. The use of a dif- fuser as the light source makes optical design much more simple and flexible than tradi- tional interferometric techniques. It allows use to consider its application on a wide range of form. We have also taken profit of the LWIR range to realise for the first time simultaneous dis- placement and temperature measurements with the same infrared detector. For this, we propose different computation techniques of the thermal image out of the phase shifted ESPI specklegram acquisitions. [less ▲]

Digital holographic interferometry by using long infrared radiation (CO2 laser)

in Advances in Experimental Mechanics VII (2010, September)

We show how digital holographic interferometry in the Long Wave InfraRed (LWIR) spectral range can be used for the investigation of mechanical structures. The 10.6 μm radiation is produced by a CO2 Laser ... [more ▼]

We show how digital holographic interferometry in the Long Wave InfraRed (LWIR) spectral range can be used for the investigation of mechanical structures. The 10.6 μm radiation is produced by a CO2 Laser. Experimental results showing that the method can be used to locate defect in a panel are presented and advantages and disadvantages of this approach are discussed [less ▲]

Electronic Speckle Pattern Interferometry at Long Infrared Wavelengths. Scattering Requirements

in Osten, Wolfgang; Kujawinska, Malgorzata (Eds.) Fringe 2009 (2009, September)