Lock-in Thermography using High-Power Laser Sources

Ziegler, Mathias; BAM Bundesanstalt fur Materialforschung und -prufung; Germany

Ziegler, M; Federal Institute for Materials Research and Testing (BAM); Germany
Thiel, E.; Federal Institute for Materials Research and Testing (BAM); Germany
Ahmadi, S.; Federal Institute for Materials Research and Testing (BAM); Germany

ID: ECNDT-0139-2018
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Session: Thermography and Thermosonics Techniques 1
Room: H1
Date: 2018-06-15
Time: 09:20 - 09:40

Optical lock-in thermography is a completely contactless and very sensitive NDT technique. As an optical source of energy, incandescent lamps are most commonly used because they are relatively inexpensive and offer high irradiances at the test specimen. However, they are strongly restricted by their low modulation bandwidth with a maximum modulation frequency of only about 1 Hz. The use of high-power kilowatt-class laser sources, e.g. diode laser arrays, pushes this constraint beyond 100 Hz. This allows for the exploration of the near-surface region of metals and layer systems with better and more accurate penetration depth and depth resolution. Moreover, these lasers are virtually free of any additional thermal radiation that could interfere with the “true” thermal response emitted from the heated sample. In turn, they can be easily used in a one-sided test configuration.
We present current activities with kilowatt-class high-power laser sources for advanced lock-in thermography and focus on the application of laser arrays that offer a very high irradiation strength over a large sample area beyond the mentioned advantages.