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

Introduction

Since its demonstration in 2003 [1], the use of long-wave infrared (LWIR) CO₂ lasers in Digital Holography (DH) has been shown in an increasing number of applications. 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 [2-4] and shearography [4]. The LWIR holographic set-up generally makes use of microbolometer arrays based thermal imagers. The present paper discusses some result of the European project FANTOM in which another advantage was put forward when speckle interferometry is applied in LWIR: the thermal background is captured simultaneously to the specklegrams since it constitutes an offset in the signal. Therefore one can correlate uniquely the temperature and displacement information at the same time and in each pixel. We describe here the successful achievements of the project.