THERMAL-DIFFUSIVITY OF ANISOTROPIC MATERIALS BY PHOTOTHERMAL METHODS

In this paper we analyze the possibility of extending the photothermal methods developed for thermal diffusivity measurements of isotropic m aterials [A. Salazar and A. Sanchez-Lavega, Rev. Sci. Instrum. 65, 289 6 (1994)] to the case of anisotropic specimens. A full theoretical tre atment of the photothermal signal generation for the case of an anisot ropic sample with its principal axes aligned with the sample surface i s presented. Three photothermal detection schemes have been studied: i nfrared radiometry, photothermal reflectance, and optical beam deflect ion (mirage effect). The fundamental result we have obtained is that w hen using infrared radiometry, photothermal reflectance and collinear mirage setups, the thermal magnitude retrieved is the resistivity to h eat diffusion (a tensor defined as the inverse of the thermal diffusiv ity tensor), Only the perpendicular mirage experiment allows one to di rectly retrieve the thermal diffusivity along any direction of the mat erial. Experimental measurements performed on two highly anisotropic m aterials confirm the above-mentioned results. (C) 1996 American Instit ute of Physics.