Probing of thermal waves generated on a sample surface has turned but to be an excellent method for non-destructive (ND) and noncontact (NC) testing and evaluation of optical and thermal properties. During past decade and a half, considerable developments in the area of photothermal wave probing has taken place and almost all possibilities of probing these waves have been exploited and have led to the development of a variety of methods/techniques [1, 2]. The various technique, in line with their nomenclature, are based on the common principle of heating of the sample with a (monochromatic) electromagnetic radiations whose intensity is time dependent. This dependence could be periodical, pulse shaped or modulated in a statistical way. The temperature increase depends in a complicated way on spatial distribution, of heat source of local absorption, of local thermal properties and finally the structure of the sample. This temperature dependence of the sample can be measured in various ways and the analysis of these optically generated thermal waves, in turn, has become a powerful tool for nondestructive and contactless inspection and evaluation of intrinsic properties of sample. The methods have wide ranging applications apart from thermal diffusivity and anisotropy investigation of subsurface cracks, voids, de-lamination and defects ranging size and depth from a few micron to a millimeter (eg. heterogeneity/homogeneity) depending upon the thermal properties of the material [3, 4]. The present paper will briefly describe. - Mirage and collinear Mirage spectroscopy
- Microscopic infra-red radiometry
The detection system in the former involves a position sensor which measures the deflection of probe beam resulting from change in refractive index of the medium (or the sample) caused as resulting of modulated heating (Mirage Effect). In case of later the emitted thermal radiations (from the sample surface) are focussed onto an infra-red detector through an infrared microscope and the output signal is fed to lock in amplifier which measures phase and amplitude of waves.
It is proposed to demonstrate a few contactless ND applications with specific examples on advanced and high tech materials like fullerenes, carbon fibre, thin films, ceramic etc.
ACKNOWLEDGEMENT:
This work is a part of project sponsored by Indo-French Center for Promotion of Advanced Research (IFCPAR). REFERENCES
- A. Mandelis, "Progress in Photothermal and Photoaconstic Science and technology" Vol-1 Elsevier 1992
- G. C. Pandey, J. Guitony, D. Fournier and A. C. Boccara, "Thermal Diffusivity of Polymers by Mirage Spectroscopy" Accepted in SPE Conf. USA
- Guitonny J. G. C. Pandey, Boccara A. C. and D. Fournier, "Thermal Diffusivity Measurements using Infra-red Microscopy, Application to Polymeric Materials", J. de Physique 4C7, 307, 1994
- G. C. Pandey, D. Fournier, and A. C. Boccara, "Thermal diffusivity and Anisotropic Effects in Transparent Polymers using colinear Mirage Detection", J. de Physique 4C7, 279 (1994)
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