Active Thermal Extraction and Temperature Sensing of Near-field Thermal Radiation

Abstract

Recently, we proposed an active thermal extraction (ATX) scheme that enables thermally populated surface phonon polaritons to escape into the far-field. The concept is based on a fluorescence upconversion process that also occurs in laser cooling of solids (LCS). Here, we present a generalized analysis of our scheme using the theoretical framework for LCS. We show that both LCS and ATX can be described with the same mathematical formalism by replacing the electron-phonon coupling parameter in LCS with the electron-photon coupling parameter in ATX. Using this framework, we compare the ideal efficiency and power extracted for the two schemes and examine the parasitic loss mechanisms. This work advances the application of ATX to manipulate near-field thermal radiation for applications such as temperature sensing and active radiative cooling.Heat transport by electromagnetic radiation is a fundamental process that plays a role in numerous applications such as thermal management in space 1,2 , radiative cooling and heating 3-7 , and energy conversion 8 . Of particular interest is how electromagnetic radiation can be used to transport heat either in passive or active schemes, and the limits of the heat transport in these schemes. For instance, although the far-field heat flux cannot exceed the blackbody limit, a number of works have experimentally demonstrated that passive near-field radiative heat transfer is enhanced by many orders of magnitude compared to the far-field limit for closely spaced objects with either natural 9-12 or engineered resonant surface modes 13 . These effects have been exploited for enhanced near-field radiative cooling but are limited to the near-field [14][15][16] . In active schemes, laser cooling of solids (LCS) enables active cooling with light by removing thermal energy in the form of phonons with upconversion fluorescence 17 but is only possible in certain solids.Recently, we theoretically proposed active thermal extraction (ATX) scheme that allows near-field electromagnetic surface waves to propagate into the far-field, thereby enhancing the total radiative flux emitted by a solid 18 . The technique operates by exploiting the monochromatic nature of near-field thermal radiation to drive a transition in a laser gain medium that, when coupled with external optical pumping, allows the resonant surface mode to be emitted into the far-field.ATX shares many similarities with LCS, particular its ability, in principle, to cool an object below ambient temperature, but is applicable to a wider range of solids than LCS.LCS was first demonstrated experimentally by Epstein et al. 19 in ytterbium-doped fluorozirconate glass and has since been experimentally demonstrated to cool other rare-earth doped glasses 20-37 and recently to cool semiconductors 38 and lead perovskites 39 . At the same time, LCS has been used as a means to measure temperature by observing the wavelengths of emitted light, with applications for temperature sensing at the nanoscale and in biological tissues [40][41][42][43][44][4...

Novel Methods to Harness Solar Radiation for Advanced Energy Applications

“…Likewise, we can use near-field heat transfer in the form of thermal radiation to perform these upconversions. The process has been 75,76 proposed recently, known as active thermal extraction, as shown in Fig. 6 (b), where instead of absorbing a phonon, the upconversion is made possible by coupling to a near-field photon.…”