Improvement of the laser flash method to reduce uncertainty in thermal diffusivity measurements

The National Metrology Institute of Japan (NMIJ) has improved the laser flash technique to reduce uncertainty in thermal diffusivity measurements of solid materials above room temperature. An advanced laser flash apparatus was constructed after the following technical improvements had been made. (i) Uniform pulse heating of a specimen was achieved with an improved laser beam using an optical fibre (decreasing the error due to nonuniform heating). (ii) A fast infrared radiation thermometer with an absolute temperature scale was developed (decreasing the error due to nonlinear temperature detection). (iii) A new data analysis algorithm employing curve-fitting method whereby the entire region of the temperature history curve is fitted by the theoretical solution under the real boundary condition was introduced (decreasing the heat loss error). The precision and accuracy of the apparatus were demonstrated by measuring specimens of glassy carbon which is a candidate reference material for a thermal diffusivity standard to be supplied by the NMIJ.