MEASUREMENT OF THERMAL-DIFFUSIVITY BY OPTICAL-EXCITATION AND INFRARED DETECTION OF A TRANSIENT THERMAL GRATING

A contactless technique is described for measuring the thermal diffusivity in a direction parallel to the surface of a thin sample by pulsed-laser excitation and thermal-radiation detection of a thermal grating on the surface. The transient thermal grating (flc) with periodicity Lambda in the range 20-1000 mu m is created with a novel interferometer which does not require a long-coherence-length laser. Fast thermometry is achieved with an infrared detector focused on a spot similar to 30 mu m in diameter to examine in detail the shape and the time dependence of the TTG. The performance of the system is demonstrated on a thin Ti foil with Lambda ranging over an order of magnitude. Data are also presented for an 11 mu m thick diamond film with a factor-of-20 higher diffusivity than for Ti. The results indicate that the system is well suited to measuring local diffusivities in regions as small as similar to 100 mu m in thin, free-standing films. (C) 1995 American Institute of Physics.