Thermal Emission of Silicon at Near-Infrared Frequencies Mediated by Mie Resonances

Planck’s law constitutes one of the cornerstones in physics. It explains the well-known spectrum of an ideal blackbody consisting of a smooth curve, whose peak wavelength and intensity depend on the temperature of the body. This scenario changes drastically, however,
when the size of the emitting object is comparable to the wavelength of the emitted radiation. Here we show that a silicon microsphere (2−3 μm in diameter) heated to around 800 °C yields a thermal emission spectrum consisting of pronounced peaks that are associated with Mie resonances. We experimentally demonstrate in the near-infrared the existence of modes with an ultrahigh quality factor, Q, of 400, which is substantially higher than values reported so far, and set a new benchmark in the field of thermal emission. Simulations predict that the thermal response of the microspheres is very fast, about 15 μs. Additionally, the possibility of achieving light emission above the Planck limit at some frequency ranges is envisaged.

Fig. 1. Experimental setup and FEM simulation of the temperature distribution and time response of the heating process of a silicon microsphere from room temperature to 750 °C

Fig. 2. Thermal emission spectra of silicon microspheres.

Figure 3. Optical absorption parameters for silicon at high temperature.

Figure 4. Demonstration of a resonance tuning by temperature and its high Q