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Interferometric Testing of Materials

IP.com Disclosure Number: IPCOM000040526D
Original Publication Date: 1987-Nov-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Kempf, J: AUTHOR [+4]

Abstract

Local surface properties of a material are analyzed by means of a two-beam phase-sensitive interferometric device in which one of the pulsed beams has a high intensity to periodically heat the surface locally and both beams are used to analyze the time-dependent growth and decay of the local thermal expansion. Fig. 1 shows an example of testing a conductor 5 embedded in a substrate 4, e.g., a printed circuit board. An intensity-modulated polarized laser beam L0 is deflected at semi-transparent mirror 2 to a birefringent crystal 3 which is oriented such that beam L0 is split into a high intensity beam L1 to be focussed on conductor 5 and a low intensity reference beam L2 impinging on substrate 4.

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Interferometric Testing of Materials

Local surface properties of a material are analyzed by means of a two-beam phase-sensitive interferometric device in which one of the pulsed beams has a high intensity to periodically heat the surface locally and both beams are used to analyze the time-dependent growth and decay of the local thermal expansion. Fig. 1 shows an example of testing a conductor 5 embedded in a substrate 4, e.g., a printed circuit board. An intensity-modulated polarized laser beam L0 is deflected at semi-transparent mirror 2 to a birefringent crystal 3 which is oriented such that beam L0 is split into a high intensity beam L1 to be focussed on conductor 5 and a low intensity reference beam L2 impinging on substrate 4. Beams L1 and L2 are reflected, recombined by crystal 3 and fed to detector 1 which analyzes the relative phase difference between the reflected beams, as described in U.S. Patent 4,298,283, for example. The conductor length is scanned by mechanical translation along arrow 6. Fig. 2 shows the time- dependent measurement signal which is typical of a thermal relaxation process. At time t0, the high intensity laser beam L1 starts heating conductor 5 which thus expands until a steady-state value H1 is reached. This value H1 depends on the absorbed energy, the local temperature and the thickness of conductor 5. At time t1, the laser beam is interrupted such that the thermal expansion decays at a relaxation time tR which depends on the therma...