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

A contactless technique is described for measuring the thermal diffusi vity 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 interferomete r which does not require a long-coherence-length laser. Fast thermomet ry 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 depend ence of the TTG. The performance of the system is demonstrated on a th in Ti foil with Lambda ranging over an order of magnitude. Data are al so presented for an 11 mu m thick diamond film with a factor-of-20 hig her diffusivity than for Ti. The results indicate that the system is w ell suited to measuring local diffusivities in regions as small as sim ilar to 100 mu m in thin, free-standing films. (C) 1995 American Insti tute of Physics.