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

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 $λ\approx 2.6\,μ$m. We have extended the range of validity of this formula for $T$ up to $T_m$ and for $λ$ up to $\approx 12\,μ$m.

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