Temperature dependent polarization of the thermal radiation emitted by thin, hot tungsten wires

TL;DR

This study measures how the linear polarization of thermal radiation from thin tungsten wires varies with temperature from just above room temperature up to melting point, confirming theoretical models over an extended range.

Contribution

First measurements of temperature-dependent polarization of tungsten wire radiation over a wide temperature and wavelength range, validating extended theoretical models.

Findings

Polarization decreases as temperature increases.

Experimental data agrees with extended Kirchhoff's law predictions.

Extended validity of optical property models for tungsten up to melting temperature.

Abstract

We report measurements of the temperature $T $ dependence of the linear polarization $\langle P\rangle $ of the thermal radiation emitted by thin, incandescent tungsten wires. We investigated an interval ranging from a little above room temperature up to melting, $T_m\approx 3700\,$K. These are the first measurements in such wide a range. We found that $\langle P\rangle $ decreases with increasing $T.$ We obtained a satisfactory agreement with the theoretical predictions based on the Kirchhoff's law by using a Drude-type formula for the optical properties of tungsten. The validity of such formula is assessed in literature for $T\leq 2400 \,$K and for wavelengths in the range from visible up to $\lambda\approx 2.6\,\mu$m. We have extended the range of validity of this formula for $T$ up to $T_m$ and for $\lambda$ up to $\approx 12\,\mu$m.