Nondestructive testing by using long-wave infrared interferometric techniques with CO₂lasers and microbolometer arrays

Abstract

We describe three different interferometric techniques (electronic speckle pattern interferometry, digital holographic interferometry, and digital shearography), using a long-wave infrared radiation produced by a CO 2 laser and recorded on a microbolometer array. Experimental results showing how these methods can be used for nondestructive testing are presented. Advantages and disadvantages of these approaches are discussed.

Speckle interferometry in the long-wave infrared for combining holography and thermography in a single sensor: applications to nondestructive testing: The FANTOM Project

“…Various techniques were considered and compared but only one was kept for building the mobile instrument. These techniques are the off-axis DHI with a frontal lens, the ESPI with phase-shifting and the shearography, which were investigated and compared in [18]. The best results were obtained by ESPI, despite some advantages of DHI which offers the possibility of single shot measurements and direct phase extraction, whereas ESPI requires 4 phase-shifted specklegram acquisitions.…”

“…We already showed achievements of LWIR DHI [17] and comparison of different LWIR interferometric techniques and optimization of an ESPI setup [18] . These works resulted in the development of a mobile ESPI head which included the CO 2 laser and a thermographic camera based on a microbolometers array.…”

Speckle interferometry at 10 micrometers wavelength: a combined thermography and interferometry technique and its application in aeronautical nondestructive testing

“…The development of the set-up we use was already presented in several papers: we studied various configurations such as LWIR DHI [17] [18] , ESPI [18] and shearography [18] . The camera is a Jenoptik Variocam HR based on an uncooled microbolometer array with 640x480 pixels, each pixel being 25 µm wide.…”

Simultaneous Temperature and Deformations Measurements Using Long-Wave Infrared Speckle Interferometry: A Novel Hybrid Technique for Industrial Nondestructive Testing

“…In particular it allows observing large objects and in metrology it allows measuring large displacements while rendering holography more immune to environmental perturbations, compared to holography in the visible. For metrology we demonstrated various holographic techniques in LWIR: speckle interferometry [2,4], DH interferometry [2][3][4] and shearography [4]. The LWIR holographic set-up generally makes use of microbolometer arrays based thermal imagers.…”