A multiwavelength reflectometric technique for normal spectral emissivity measurements by a pulse-heating method

A new technique has been developed for the direct measurement of the normal spectral emissivity at several wavelengths in pulse-heating conditions at HIT, adding some novel features to previous versions of this type of apparatus. Pulse-heating experiments were performed on niobium strip specimens, taking the specimen from room temperature to the melting point using rapid resistive self-heating. The normal spectral emissivity at three wavelengths was measured by a multi-wavelength reflectometric technique developed at HIT. At the same time, the radiance temperature was measured at the same wavelengths by a high-speed pyrometer from approximately 1000 K to the melting point. Details of the method, of the measurement apparatus and of the calibration technique are described. Preliminary results of the normal spectral emissivity of niobium at 633 nm, 750 nm and 900 nm in a wide temperature range are presented.