Microsecond-Resolution Laser Polarimetry for the Measurement of the Normal Spectral Emissivity of Pulse-Heated Materials

Author(s)

Sitaraman Krishnan, K Boboridis

Abstract

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.

Citation

Review of Scientific Instruments

Pub Type

Journals

Keywords

emissivity, liquid metals, niobium, polarimetry, pulse calorimetry, thermophysical properties

Citation

Krishnan, S. and Boboridis, K. (1970), Microsecond-Resolution Laser Polarimetry for the Measurement of the Normal Spectral Emissivity of Pulse-Heated Materials, Review of Scientific Instruments (Accessed July 27, 2024)