Dynamic optical control of near-field radiative transfer

Dynamic control of radiative heat transfer is of fundamental interest as well as for applications in thermal management and energy conversion. However, realizing high contrast control of heat flow without moving parts and with high temporal frequencies remains a challenge. Here, we propose a thermal modulation scheme based on optical pumping of semiconductors in near-field radiative contact. External photo-excitation of the semiconductor emitters leads to increases in the free carrier concentration that in turn alters the plasma frequency, resulting in modulation of near-field thermal radiation. The temporal frequency of the modulation can reach hundreds of kHz limited only by the recombination lifetime, greatly exceeding the bandwidth of methods based on temperature modulcation. Calculations based on fluctuational electrodynamics show that the heat transfer coefficient between two silicon films can be tuned from near zero to 600 Wm^-2K^-1 with a gap distance of 100 nm at room temperature.