Photothermal beam-deflection imaging of vertical interfaces in solids

Abstract

A new method for calculating signals in photothermal beam-deflection imaging is reviewed and applied to the case of vertical interfaces (cracks or other thermal barriers) in opaque solids. The generality of the approach and the effect of finite probe-beam size are emphasized.On prtsente une nouvelle methode pour le calcul des signaux en imagerie photo-thermique par dtflection de faisceau, qui est Cgalement appliqute au cas d'interfaces verticales (fissures ou autres barrikres thermiques) dans des solides opaques. Le gtntralite de l'approche et I'effet de la dimension finie du fasiceau-sonde sont particulikrement dtveloppts.

Nonlinear effects in photothermal-optical-beam-deflection imaging

“…Line scans of the PTOBD signal (amplitude and phase) in the neighborhood of the interface were obtained at several values of frequency and pump-laser power. The shape and frequency dependence were characteristic of a planar, thermal resistance perpendicular to the surface (12). The scans included regions sufficiently far from the interface that the PTOBD signal showed no indication of its presence; the signal from those far regions is regarded to be due to the homogeneous bulk of the crystal.…”

Photothermal characterization of vertical and slanted thermal barriers: A quantitative comparison of mirage, thermoreflectance, and infrared radiometry

“…The first method is valid for situations with cylindrical symmetry ͑case of vertical barriers͒ and makes use of the Hankel transform and Green's functions. 3 The second method is applicable to more general barrier configurations ͑tilted, buried, and size limited barriers͒ but is restricted to low R T values. It makes use of the Green's function theorem and the Born approximation.…”

“…1 A particular topic which has been addressed in the past using these methods has been the detection and characterization of vertical and highly tilted thermal barriers within homogeneous samples or as interfaces separating two different media. [2][3][4][5][6][7][8][9] Photothermal methods based on modulated and localized excitation on the sample surface have proved effective for such task. Among them, a group of sensitive, noncontact techniques including the ''mirage'' effect ͑or optical beam deflection͒, thermoreflectance ͑also called photoreflectance͒, and infrared radiometry are widely employed.…”

Photothermal mirage characterization of vertical interfaces separating two different media

“…8 Moreover, we make also use of Green's function to get an analytical integral solution in the same way as described in other works. 3,8 The surface temperature at any point T s can be represented as T s (x,y)ϭT 1 (x,y)ϩT 2 (x,y) where T i (x,y) is the temperature in each part ͑iϭ1, yϽ0; iϭ2, yϾ0͒. Passing the details of the calculation, 8 T i (x,y), is given by…”

“…1 Among them the ''mirage'' technique ͑or optical beam deflection͒ has become popular because of its high sensitivity to detect near-subsurface structures and in particular vertical and tilted thermal barriers. [2][3][4][5][6] In such a ''mirage'' experience, thermal waves generated in a solid ͑in its surface if the material is optically opaque͒ by the absorption of a modulated pump light beam propagate diffusively through the sample, being scattered backward and forward by the subsurface structure. For a thermally thick material ͑thickness much larger than thermal wavelength͒ containing close subsurface features and because of the damped nature of the thermal waves, detection of backward scattered waves is preferred.…”