Location

La Jolla ,CA

Start Date

1-1-1989 12:00 AM

Description

Kuo and Munidasa [1] have reported a method by which a time-dependent optical intensity pattern is produced by the interference of laser light diffracted from a thermally induced bump with the light of the same laser reflected from the plane of the sample on which the bump was induced. In their experiment the thermal bump was induced by a second laser beam which was optically incoherent with the interfering light, but which was intensity modulated at frequencies ranging from the audio to the ultrasonic range. The resulting time-dependent patterns carry information about the thermal and elastic properties of the sample. The purpose of this work is to provide a first-principles calculation of those patterns so that those material properties can be measured with this technique. The starting point of the calculation is the solution to the coupled thermoelastic equations developed by Favro et al. [2–4]. That solution is expressed in terms of the three eigenmodes of the coupled equations: (1) a longitudinal acoustic wave consisting of propagating particle displacements and associated temperature variations arising from the compression and rarefaction of the material; (2) a transverse (shear) wave which consists only of propagating particle displacements and which does not cause any temperature variation as it propagates; and (3) a heavily-damped thermal wave which consists of propagating temperature variations and associated particle displacements arising from the thermal expansion it causes. The combination of surface displacements (i.e. “thermal bump”) resulting from these three kinds of waves when a modulated laser beam is incident on the surface of an opaque solid can be calculated in a straight forward fashion from expressions given in [4].

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

8A

Chapter

Chapter 2: Advanced Techniques

Section

Other New Techniques

Pages

635-640

DOI

10.1007/978-1-4613-0817-1_80

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Single Beam Interferometry of a Thermal Bump: II—Theory

La Jolla ,CA

Kuo and Munidasa [1] have reported a method by which a time-dependent optical intensity pattern is produced by the interference of laser light diffracted from a thermally induced bump with the light of the same laser reflected from the plane of the sample on which the bump was induced. In their experiment the thermal bump was induced by a second laser beam which was optically incoherent with the interfering light, but which was intensity modulated at frequencies ranging from the audio to the ultrasonic range. The resulting time-dependent patterns carry information about the thermal and elastic properties of the sample. The purpose of this work is to provide a first-principles calculation of those patterns so that those material properties can be measured with this technique. The starting point of the calculation is the solution to the coupled thermoelastic equations developed by Favro et al. [2–4]. That solution is expressed in terms of the three eigenmodes of the coupled equations: (1) a longitudinal acoustic wave consisting of propagating particle displacements and associated temperature variations arising from the compression and rarefaction of the material; (2) a transverse (shear) wave which consists only of propagating particle displacements and which does not cause any temperature variation as it propagates; and (3) a heavily-damped thermal wave which consists of propagating temperature variations and associated particle displacements arising from the thermal expansion it causes. The combination of surface displacements (i.e. “thermal bump”) resulting from these three kinds of waves when a modulated laser beam is incident on the surface of an opaque solid can be calculated in a straight forward fashion from expressions given in [4].