Subsecond Measuring Technique for In-plane Thermal Diffusivity at Local Area by the Forced Rayleigh Scattering Method

In the course of a chemical reaction or structural changes in a material, the thermal diffusivity of the material changes in response to its varying conditions. Real-time information in the form of successive data on the thermal diffusivity during the process is indispensable for an adaptive control system for material production or processing. In the present study, a measurement technique for in-plane thermal diffusivity in micro-scale and at a high repetition rate has been studied. In view of the application of this method for fast processes, the effects of property changes during a single measurement time on the measured value have been quantitatively evaluated. We have developed a measurement system of the in-plane thermal diffusivity by means of the forced Rayleigh scattering method, an optical technique with a measurement time less than 1 ms and at a micro-scale local observation area. In the present system, each thermal diffusivity measurement was conducted every 10 ms; i.e., the repetition rate was up to 100 data per second. The results of preliminary measurements of a polymethylmethacrylate plate with several repetition rates verify the reliability of this technique in tracing high-speed phenomena