Figure 7: Absorptivity and emissivity at high temperature.

Experimental observation of the OTT at high temperatures through normal incidence absorptivity measurements for the tungsten/hafnium dioxide metamaterial emitter at temperatures of 23, 300, 500 and 600 °C. The black line represents the experimental emissivity spectrum at normal incidence of the metamaterial emitter at a temperature of 1,000 °C. The expected slight increase of the electron collision frequency at high temperatures leads to slightly increasing absorptivities and emissivities in metals. The emission peak and the long-wavelength suppression show only a small variation from room temperature up to 1,000 °C, confirming that the topological transition of the metamaterial emitter is thermally robust, and highlighting the potential of the emitter for TPV applications.