If properly designed, terrestrial structures can passively cool themselves through radiative emission of heat to outer space. For the first time, we present a metal-dielectric photonic structure ...capable of radiative cooling in daytime outdoor conditions. The structure behaves as a broadband mirror for solar light, while simultaneously emitting strongly in the mid-IR within the atmospheric transparency window, achieving a net cooling power in excess of 100 W/m(2) at ambient temperature. This cooling persists in the presence of significant convective/conductive heat exchange and nonideal atmospheric conditions.
Cooling is a significant end-use of energy globally and a major driver of peak electricity demand. Air conditioning, for example, accounts for nearly fifteen per cent of the primary energy used by ...buildings in the United States. A passive cooling strategy that cools without any electricity input could therefore have a significant impact on global energy consumption. To achieve cooling one needs to be able to reach and maintain a temperature below that of the ambient air. At night, passive cooling below ambient air temperature has been demonstrated using a technique known as radiative cooling, in which a device exposed to the sky is used to radiate heat to outer space through a transparency window in the atmosphere between 8 and 13 micrometres. Peak cooling demand, however, occurs during the daytime. Daytime radiative cooling to a temperature below ambient of a surface under direct sunlight has not been achieved because sky access during the day results in heating of the radiative cooler by the Sun. Here, we experimentally demonstrate radiative cooling to nearly 5 degrees Celsius below the ambient air temperature under direct sunlight. Using a thermal photonic approach, we introduce an integrated photonic solar reflector and thermal emitter consisting of seven layers of HfO2 and SiO2 that reflects 97 per cent of incident sunlight while emitting strongly and selectively in the atmospheric transparency window. When exposed to direct sunlight exceeding 850 watts per square metre on a rooftop, the photonic radiative cooler cools to 4.9 degrees Celsius below ambient air temperature, and has a cooling power of 40.1 watts per square metre at ambient air temperature. These results demonstrate that a tailored, photonic approach can fundamentally enable new technological possibilities for energy efficiency. Further, the cold darkness of the Universe can be used as a renewable thermodynamic resource, even during the hottest hours of the day.
We present theoretical considerations as well as detailed numerical design of absorber and emitter for Solar Thermophotovoltaics (STPV) applications. The absorber, consisting of an array of tungsten ...pyramids, was designed to provide near-unity absorptivity over all solar wavelengths for a wide angular range, enabling it to absorb light effectively from solar sources regardless of concentration. The emitter, a tungsten slab with Si/SiO(2) multilayer stack, provides a sharp emissivity peak at the solar cell band-gap while suppressing emission at lower frequencies. We show that, under a suitable light concentration condition, and with a reasonable area ratio between the emitter and absorber, a STPV system employing such absorber-emitter pair and a single-junction solar cell can attain efficiency that exceeds the Shockley-Queisser limit.
The Jaynes-Cummings (JC) system, which describes the interaction between a cavity and a two-level atom, is one of the most important systems in quantum optics. We obtain analytic solutions for the ...one- and two-photon transport in a waveguide side-coupled to the JC system using input-output formalism in Fock space. With these results, we discuss the conditions under which the JC system functions as a photon switch for waveguide photons in both the strong and weak coupling regimes.
This dissertation deals with two disparate regimes of light: Thermal emission of light from nanostructured and microstructured surfaces, and light emission and scattering from isolated quantum ...multi-level systems such as atoms or quantum dots. We show that wavelength-scale structuring of materials can lead to strong modification of light absorption and emission properties, and that such properties can lead to improvements in the efficiency of solar energy conversion and can enable passive cooling via emission of radiation even during the daytime hours. We also study the fully quantum-mechanical interaction of few-photon states with isolated quantum multi-level systems (emitters), whose physical manifestation can take the form of atoms, superconducting qubits, and quantum dots. Through this study we obtain analytical solutions to the propagation of photons through these important system. Specifically, we gain new insight into atom inversion, fluorescence quenching, two-photon state engineering, dissipation, and provide the first fully quantum mechanical description of stimulated emission in the most fundamental case of a single-photon, interacting with a single excited atom.
The Jaynes-Cummings (JC) system, which describes the interaction between a cavity and a two-level atom, is one of the most important systems in quantum optics. We obtain analytic solutions for the ...one- and two-photon transport in a waveguide side-coupled to the JC system using input-output formalism in Fock space. With these results, we discuss the conditions under which the JC system functions as a photon switch for waveguide photons in both the strong and weak coupling regimes
We study stimulated emission from an excited two-level atom coupled to a waveguide containing an incident single-photon pulse. We show that the strong photon correlation, as induced by the atom, ...plays a very important role in stimulated emission. Additionally, the temporal duration of the incident photon pulse is shown to have a marked effect on stimulated emission and atomic lifetime.
We calculate the one- and two-photon scattering matrices of a pair of collocated non-identical two-level atoms coupled to a waveguide. We show that by proper choice of a two-photon input, the ...background fluorescence by the atoms may be completely quenched, as a result of quantum interference, and that when the atoms' detuning is smaller than their linewidths, extremely narrow fluorescence features emerge. Furthermore, the system emits a two-photon bound state which can display spatial oscillations/quantum beats, and can be tuned from bunched to anti-bunched statistics as the total photon energy is varied.
PDF
