Near-field refrigeration and tunable heat exchange through four-wave mixing

We modify and extend a recently proposed four-wave mixing scheme [Opt. Express 25 (19),23164 (2017)] for achieving near-field thermal upconversion and energy transfer, to demonstrate efficient thermal refrigeration at low intensities $\sim 10^{-9}$W/m$^2$ over a wide range of gap sizes (from tens to hundreds of nanometers) and operational temperatures (from tens to hundreds of Kelvins). We further exploit the scheme to achieve magnitude and directional tunability of near-field heat exchange between bodies held at different temperatures.