Optically controlled radiative transfer in the near field

Actively controlling the heat flow is of great importance for applications of cooling, heating, and energy conversion. It is extremely difficult to achieve high contrast heat flow without moving parts. Here, we propose a thermal modulation scheme based on optical pumping of semiconductors in near-field radiative contact. External photoexcitation of one semiconductor leads to changes in carrier concentration that in turn alters the plasma frequency of silicon, leading to drastic modulation of near field thermal radiation. Calculations based on fluctuational electrodynamics show that the heat transfer coefficient can be tuned from ~ 10 W m^-2 K^-1 to ~200 W m^-2 K^-1 with a gap distance of 100 nm at room temperature.