Nature 566, 239–244 (2019)

While coherent laser radiation is usually required in optical cooling schemes such as Doppler cooling, recent work has suggested that optical cooling may be possible simply using a conventional photodiode instead. The idea, however, requires precisely parallel nanogaps of vanishingly small gap widths. And, the measurement of the cooling itself is also a challenge. Now, Linxiao Zhu and colleagues at the University of Michigan, USA, claim to have experimentally achieved this feat and report room-temperature, high-vacuum (10–6 torr) optical cooling in a nanocalorimetric device adjacent to a photodiode. The team place the planar surface of the calorimeter at nanoscale distances from the planar surface of a photodiode with extreme precision using a custom nanopositioner that enables the gap angle and distance to be controlled with 2.5-nm resolution. For a sufficiently small enough gap (less than 10 nm or so), optical near-field coupling occurs and cooling of the calorimetric device results due to enhanced transport of photons across the gap. Additionally, the photodiode is held under reverse bias to suppress photon emission. In the future, such nanophotonic cooling may enable new opportunities for on-chip solid-state refrigeration of optoelectronics.

Credit: Springer Nature Limited