Microsecond-Resolution Laser Polarimetry for the Measurement of the Normal Spectral Emissivity of Pulse-Heated Materials
Sitaraman Krishnan, K Boboridis
The design and operating principles of a new laser polarimeter system capable of microsecond-resolution measurements of the polarization state of light and of optical properties of solid and liquid materials, including the normal spectral emissivity, are described. This high-speed polarimeter has been applied to measurements of the normal spectral emissivity of pulse-heated materials in conjunction with radiation thermometry to achieve true-temperature measurements on a microsecond time scale. Amplitude-modulated, polarized laser light is reflected from thin, wire-shaped specimens, and the polarization state of the reflected light is measured with the laser polarimeter using ultra-high-speed detectors combined with phase-sensitive detection and a fast data acquisition system. The optical properties and the normal spectral emissivity are then derived from the measured change in the polarization state. Preliminary measurements on the liquid-state optical properties of niobium are presented as a validation of this new system. The measured value for the normal spectral emissivity of liquid niobium from its melting point up to 3350 K was 0.34 + 0.03. In conjunction with radiation thermometry, the melting temperature of niobium, as measured with the new system, was 2737 K + 25 K. Potential applications of this new technology are described in the context of true temperature and thermophysical property measurements.
and Boboridis, K.
Microsecond-Resolution Laser Polarimetry for the Measurement of the Normal Spectral Emissivity of Pulse-Heated Materials, Review of Scientific Instruments
(Accessed December 8, 2023)