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

• The thermal radiation emitted by thin tungsten wires is polarized perpendicular to their axis.
• The polarization decreases with temperature increasing from room temperature to melting.
• The temperature dependence of polarization is described by the theory of light scattering.
• The validity range of the Drude–Lorentz formula for the dielectric constant of tungsten is extended.

We report measurements of the temperature T dependence of the linear polarization 〈P〉 of the thermal radiation emitted by thin, incandescent tungsten wires in a range from a little above room temperature up to melting Tm ≈ 3700 K across the visible and infrared range. These are the first measurements in such wide a temperature range. We found that 〈P〉 decreases with increasing T. The theoretical prediction based on Kirchhoff's law satisfactorily reproduces the experimental data if a Drude-type formula for the optical properties of tungsten is used, provided that its validity, assessed in literature only for T ≤ 2400 K and for wavelengths in the range from visible up to λ ≈ 2.6 μm, is extended to the ranges investigated in the present experiment, namely for T up to Tm and for λ up to ≈15 μm.

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