Emissivity of liquid germanium in visible and near infrared region

The normal emissivity of liquid germanium was determined from the direct measurement of the thermal radiation from the liquid surface and a blackbody. The monochromatic emissivity in the visible region and the average emissivity in the near infrared region were measured to investigate the wavelength dependence. The emissivity of the liquid has little dependence on the wavelength and is $\text{0.217±0.002}$ for the visible region (600–900 nm) and is $\text{0.200±0.005}$ for the near infrared region at the melting point. The emissivity has a weak dependence on the temperature from 910 to 1160 °C. The weak dependence agrees well with a dielectric response of the free electrons.