A5089342501- Thermal Radiation and Cooling Technologies
- Photonic and Optical Devices
- Urban Heat Island Mitigation
- Photonic Crystals and Applications
- Building Energy and Comfort Optimization
- Metamaterials and Metasurfaces Applications
- solar cell performance optimization
- Plasmonic and Surface Plasmon Research
- Thin-Film Transistor Technologies
- Optical properties and cooling technologies in crystalline materials
- Optical Coatings and Gratings
- Quantum Electrodynamics and Casimir Effect
- Radiative Heat Transfer Studies
- Solar Thermal and Photovoltaic Systems
- Advanced Thermodynamics and Statistical Mechanics
- Astrophysics and Star Formation Studies
- Neural Networks and Reservoir Computing
- Gyrotron and Vacuum Electronics Research
- Atmospheric aerosols and clouds
- Advanced Fiber Laser Technologies
- Quantum, superfluid, helium dynamics
- Nanowire Synthesis and Applications
- Near-Field Optical Microscopy
- Semiconductor Lasers and Optical Devices
- Quantum Mechanics and Non-Hermitian Physics
University of California, Los Angeles
2019-2024
California NanoSystems Institute
2022-2023
Stanford University
2010-2018
University of Pennsylvania
2018
Imperial College London
2015
The University of Texas at Dallas
2009
Microsoft (United States)
2007
Harvard University
2006
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 cooling in daytime outdoor conditions. The behaves as broadband mirror for solar light, while simultaneously emitting strongly mid-IR within atmospheric transparency window, achieving net power excess 100 W/m(2) at ambient temperature. This persists presence significant convective/conductive...
Abstract Radiative cooling technology utilizes the atmospheric transparency window (8–13 μm) to passively dissipate heat from Earth into outer space (3 K). This has attracted broad interests both fundamental sciences and real world applications, ranging passive building cooling, renewable energy harvesting refrigeration in arid regions. However, temperature reduction experimentally demonstrated, thus far, been relatively modest. Here we theoretically show that ultra-large for as much 60 °C...
Establishing the fundamental limit of nanophotonic light-trapping schemes is paramount importance and becoming increasingly urgent for current solar cell research. The standard theory light trapping demonstrated that absorption enhancement in a medium cannot exceed factor 4 n 2 / sin θ , where refractive index active layer, angle emission cone surrounding cell. This theory, however, not applicable regime. Here we develop statistical temporal coupled-mode based on rigorous electromagnetic...
Significance The coldness of the universe is an enormous but strikingly underexploited thermodynamic resource. Its direct utilization on Earth therefore represents important frontier for renewable energy research. In many applications, including solar cells and outdoor structures, absorption sunlight intrinsic either from operational or aesthetic considerations, resulting heating by undesirable. Here we experimentally demonstrate a thermal photonic scheme that can cool these structures...
Standard solar cells heat up under sunlight. The resulting increased temperature of the cell has adverse consequences on both its efficiency and reliability. We introduce a general approach to radiatively lower operating through sky access, while maintaining absorption. first present an ideal scheme for radiative cooling cells. For example case bare crystalline silicon cell, we show that can passively by 18.3 K. then demonstrate microphotonic design based real material properties approaches...
We use a rigorous electromagnetic approach to analyze the fundamental limit of light-trapping enhancement in grating structures.This can exceed bulk 4n 2 , but has significant angular dependency.We explicitly show that 2D gratings provide more than 1D gratings.We also effects profile's symmetry on absorption limit.Numerical simulations are applied support theory.Our findings general guidance for design structures solar cells.
We introduce a general approach to radiatively lower the temperature of structure, while preserving its color under sunlight. The cooling effect persists in presence considerable convective and conductive heat exchange for different solar absorptances.
We formulate the photonic band structure calculation of any lossless dispersive crystal and optical metamaterial as a Hermitian eigenvalue problem. further show that eigenmodes such systems provide an orthonormal basis, which can be used to rigorously describe behavior lossy in general.
Multilayer optical films have been extensively used in technology, but the design of multilayer structures for broadband applications is often challenging due to need incorporate material dispersion. Here, we present an implementation a memetic algorithm based on mixed integer programming, which especially suited practical optimization layered thin-film materials. In our implementation, variables consist list discrete that represents different dielectric materials, along with continuous...
We investigate the properties of two-dimensional parity-time symmetric periodic systems whose non-Hermitian periodicity is an integer multiple underlying Hermitian system's periodicity. This creates a natural set degeneracies that can undergo thresholdless PT transitions. derive k·p perturbation theory suited to continuous eigenvalues such in terms modes system. In photonic crystals, transitions are shown yield significant control over band structure system, and result all-angle...
For decades, progress in the field of optical (including solar) energy conversion was dominated by advances conventional concentrating optics and materials design. In recent years, however, conceptual technological breakthroughs fields nanophotonics plasmonics combined with a better understanding thermodynamics photon energy-conversion processes reshaped landscape schemes devices. Nanostructured devices that make use size quantization effects to manipulate density states offer way overcome...
A central challenge in the development of nanophotonic structures is identifying optimal design for a target functionality, and understanding physical mechanisms that enable optimized device's capabilities. Previously investigated methods structures, including both conventional optimization approaches as well nascent machine learning (ML) strategies, have made progress, yet they remain 'black boxes' lack explanations their predictions. Here we demonstrate convolutional neural networks (CNN)...
Complex nanophotonic structures hold the potential to deliver exquisitely tailored optical responses for a range of applications. Metal-insulator-metal (MIM) metasurfaces arranged in supercells, instance, can be by geometry and material choice exhibit variety absorption properties resonant wavelengths. With this flexibility, however, comes vast space design possibilities that classical paradigms struggle effectively navigate. To overcome challenge, here we demonstrate tandem residual network...
While passive radiative cooling has shown great potential in temperate regions lowering surface temperatures, its performance under tropical climate that is characterised by high solar irradiance and humidity still lacks exploration. Herein, we adopt a highly reflective polymeric coating with BaSO4 particles dispersed P(VdF-HFP) matrix for the tropics. Through strong Mie scattering of sunlight intrinsic bond vibration, substrate-independent average reflectance infrared emittance within 8–13...
With the gradually warming climate, global cooling demand for buildings is rapidly increasing. Radiative (RC) has been an attractive electricity-free approach to reducing energy consumption of buildings. Current RC strategies focus on roofs; however, limited attention paid vertical walls. Here, we report a zigzag-based structural design with asymmetric emissivity realize optimal Such asymmetry leads daily average temperature drop 2.3°C compared conventional walls coated materials. When...
A body that violates Kirchhoff's law of thermal radiation exhibits an inequality in its spectral directional absorptivity and emissivity. Achieving such is fundamental interest as well a prerequisite for achieving thermodynamic limits photonic energy conversion
We use a rigorous electromagnetic approach to develop light-trapping theory, which reveals that the conventional limit can be substantially surpassed in nanophotonic regimes, opening new avenues for highly efficient solar cells.
Organic bulk heterojunction solar cells are a promising candidate for low-cost next-generation photovoltaic systems. However, carrier extraction limitations necessitate thin active layers that sacrifice absorption internal quantum efficiency or vice versa. Motivated by recent theoretical developments, we show dielectric wavelength-scale grating structures can produce significant resonances in realistic organic cell architecture. We numerically demonstrate 1D, 2D and multi-level ITO-air...
Generating power at night has recently stimulated interest in using the radiative cooling mechanism with thermoelectric generators (TEGs). These low temperature and passive devices have been shown to generate electricity no active input of heat needed. Here, we optimize both geometry operating conditions driven (RC-TE) generators. We determine optimal conditions, including maximum point efficiency point, by developing a combined thermal electrical model. Our results show that condition...