Abstract
Nearly all thermal radiation phenomena involving materials with linear response can be accurately described via semi-classical theories of light. Here, we go beyond these traditional paradigms to study a nonlinear system that, as we show, requires quantum theory of damping. Specifically, we analyze thermal radiation from a resonant system containing a χ(2) nonlinear medium and supporting resonances at frequencies ω1 and ω2 ≈ 2ω1, where both resonators are driven only by intrinsic thermal fluctuations. Within our quantum formalism, we reveal new possibilities for shaping the thermal radiation. We show that the resonantly enhanced nonlinear interaction allows frequency-selective enhancement of thermal emission through upconversion, surpassing the well-known blackbody limits associated with linear media. Surprisingly, we also find that the emitted thermal light exhibits non-trivial statistics (g(2)(0) ≠ ~2) and biphoton intensity correlations (at two distinct frequencies). We highlight that these features can be observed in the near future by heating a properly designed nonlinear system, without the need for any external signal. Our work motivates new interdisciplinary inquiries combining the fields of nonlinear photonics, quantum optics and thermal science.
Highlights
Nonlinear interactions between light fields are typically weak inside bulk media but they can be significantly enhanced in resonant systems to observe them at low optical powers
Our quantum theoretic approach describes the thermal equilibrium behavior of the coupled oscillators reasonably well. We note that it cannot be adequately captured by semi-classical Langevin theory which is otherwise useful in the linear regime [16, 17] and for isolated nonlinear oscillators [4, 22]
We provided a new mechanism of enhancing the far-field thermal emission beyond the linear blackbody limits via nonlinear upconversion
Summary
Nonlinear interactions between light fields are typically weak inside bulk media but they can be significantly enhanced in resonant systems to observe them at low optical powers. The problem of thermal radiation from a passive system of coupled resonators of distinct frequencies remained unsolved We solve it here using quantum theory for a system containing a χ(2) nonlinear medium and discover new fundamental possibilities for the field of thermal radiation. In the classical regime ( ω kBT ), both oscillators have equal average thermal energy (kBT ) by the equipartition law If they are nonlinearly coupled, we expect that thermally driven upconversion and downconversion processes are balanced and thermal equilibrium with the reservoir is maintained. In the context of this interesting topic [23–25, 32], we note that Kirchhoff’s law is not applicable in the present work and the mechanism of nonlinear upconversion paves the way for a regime beyond the super-Planckian enhancement. We are confident that recent theoretical inquiries including this work will motivate the experiments in the future because of their fundamentally advancing nature and practical utility
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
