Entropy Driven Multi-Photon Frequency Up-Conversion

Abstract

Frequency up-conversion of few low-energy photons into a single high-energy photon, greatly contributes to imaging, light sources, detection and other fields of research 1-3 . However, it offers negligible efficiency when up-converting many photons. This is because coherent process are fundamentally limited due to momentum conservation requirements 4 , while in incoherent upconversion the finite intermediate states lifetime requires huge intensities. Thermodynamically, conventional incoherent up-conversion is driven by the internal energy of the incoming photons. However, a system can also drive work through change in its collective properties such as entropy. Here we experimentally demonstrate entropy driven ten-fold up-conversion from 10.6μ to 1μm at internal efficiency above 27% and total efficiency above 10%. In addition, the emitted radiance at 1μm exceeds the maximal possible Black-Body radiance of our device, indicating emitter's effective-temperature that is considerably above the bulk-temperature. This work opens the way for up-conversion of thermal-radiation, and high-temperature chemistry done at room-temperature.Traditional frequency up-conversion effects include coherent (second, third and parametric upconversion 2,5,6 and incoherent (two photon 7-9 and multi-photon absorption 10 ) processes, yet they all offer negligible efficiency when converting many (~Ten) photons into a single high-energy photon. This negligible conversion-efficiency is due to the large momentum mismatch between the pump and the produced frequencies, and the need for many photons to interact

Heat meets light on the nanoscale

“…One possible realization of a hybrid solar energy converter using heat-assisted photoluminescence has recently been proposed [15,73,74,[224][225][226], and is schematically illustrated in Figure 9b. In such a converter, solar radiation is absorbed in a low-bandgap photo-luminescent emitter, which is kept at high temperature.…”

“…This enables generation of a higher energy flux than equilibrium blackbody radiation at the same temperature of the emitter (see Figure 1a). This approach forms the basis for the operation of the hybrid energy converter based on the heat-enhanced anti-Stokes luminescence ( Figure 9b) [15,73,74,224]. Another approach makes use of the dramatic enhancement of the local photon DOS in the near-field of a thermal emitter to increase the radiative power of a thermal source [61].…”

“…Finally, as the heat-enhanced anti-Stokes spontaneous emission and scattering processes enable photon energy up-conversion, they can be used to increase the efficiency of solar energy conversion processes. One possible realization of a hybrid solar energy converter using heatassisted photoluminescence has recently been proposed 15,73,74,[224][225][226] , and is schematically illustrated in Fig. 9b.…”