Photonic Refrigeration from Time-Modulated Thermal Emission

We develop theoretical and computational formalisms to describe thermal radiation from temporally modulated systems. We show that such a modulation results in a photon-based active cooling mechanism. This mechanism has a high thermodynamic performance that can approach the Carnot limit. Our work points to exciting new avenues in active, time-modulated control of thermal emission for cooling and energy harvesting applications.

Figure 1

(a) General setup of a thermal photonic refrigerator operating between a cold side at $T_c$ and a hot side $T_h$ by coupling two modes at frequencies ${\omega }_{1,2}$ using time-modulation (purple arrow). (b) Net cooling power (blue curve) and work input (red curve) normalized to $k_B{T}_c\gamma$, as a function of the ratio of the frequencies of the two modes for $T_h=300\mathrm{K}$ and $T_c=290\mathrm{K}$ at $V=2\gamma$. (c) Coefficient of performance (COP) of the refrigerator normalized to the Carnot bound.

Figure 2

(a) Physical structure to demonstrate cooling induced by modulation. All parameters in the main text. Calculated emission spectrum of the two modes in the structure (solid blue lines) superimposed by a coupled mode theory fit (red dotted lines) for (b),(c) the unmodulated structure, (d),(e) for $\delta =0.1$ and (f),(g) for $\delta =0.5$. Modulation frequency $\mathrm{\Omega }=2\pi ·1.64\mathrm{THz}$. (h) Net cooling of the cold side (blue) and work input (red) to the modulated layers for the single channel, as a function of the modulation strength $\delta$. (i) The corresponding COP. The COP approaches a value of 5.18 for large $\delta$.

Figure 3

Spectral heat flux in both forward (blue) and reverse (red) directions in for the structure of Fig. 2 for (a) the unmodulated structure at $T_h=T_c=300\mathrm{K}$ and (b) for $\delta =0.5$, $T_c=290\mathrm{K}$, and $T_h=300\mathrm{K}$. In (a), the two curves overlay perfectly over each other due to the absence of modulation. (c) COP of the modulated structure as a function of modulation strength $\delta$. (d) Variation in the resonant frequencies of the two resonant modes in the structure of Fig. 2 as a function of the emission direction.