D3.2 - Non-Destructive Imaging and Spectroscopy Methods using Laser Light

AMA Conferences 2015
2015-05-19 - 2015-05-21
Nürnberg, Germany
Proceedings SENSOR 2015
D3 - Optical Measurement Technology
H. Grün, B. Reitinger, A. Buchsbaum, S. Katletz - RECENDT Research Center for Non-Destructive Testing GmbH, Linz (Austria)
550 - 554


Plenty of optical measurement technologies use lasers. Three technologies using a laser in different ways to acquire various parameters are presented in this work. In Optical Coherence Tomography (OCT) the photons are utilized for imaging. In OCT photons which are backscattered at interfaces within the sample can be measured by using a white light interferometer. This provides a good axial resolution but in general, OCT is limited only to a little imaging depth because of the need of ballistic, non-scattered photons. In laser ultrasound technology short laser pulses are used to generate ultrasonic waves without any physical contact. Short laser pulses are absorbed at the surface and thereby broadband ultrasonic signals launched. The wave propagates through the sample and is reflected and backscattered on interfaces. A laser vibrometer is used for non-contact measurement of the ultrasonic waves arriving at the sample surface. Terahertz imaging and spectroscopy uses a laser to produce the waves necessary for imaging. Laser pulses in the range of femto seconds excite terahertz pulses in a photoconductive antenna. During the propagation of the terahertz radiation trough the sample under investigation the waves experience attenuation and retardation which can be detected with an additional photoconductive antenna. Besides imaging, the terahertz pulse also can be Fourier transformed for spectroscopic applications. All these non-destructive testing methods uses laser light to gain different information at different imaging depth and spatial resolutions for different materials and applications.