Conventional optical devices use geometry and refractive index of materials as design tools. The real part of the refractive index is often the only significant part used in designs. But, the imaginary index is also an equally important design parameter. Here, we demonstrate a novel thermal light source using the imaginary refractive index as a design parameter. Employing non-Hermitian physics, we demonstrate a directional thermal emitter that suppresses thermal emission on one side of the metasurface in a desired spectral window for enhancing thermal imaging through it. In another case, we build an extremely spectrally selective thermal emitter for thermophotovoltaic conversion of heat to electricity. We demonstrate that the non-Hermitian thermal emitter greatly enhances conversion efficiency.
Aligned carbon nanotubes (CNTs) make a promising platform for thermal radiation applications due to their broadband IR hyberbolic dispersion and their ability to withstand high temperatures. However, their temperature dependent optical properties remain to be explored. Previously, the thermal stability of CNTs have been studied in helium and hydrogen atmospheres and vacuum, yet ambient air is yet to be explored. Here, we study optical properties of aligned CNTs at high temperatures in ambient air. We show that these films can withstand high temperatures when coated with a thin layer of dielectric and exhibit broadband IR hyperbolic dispersion at elevated temperatures.
Many emerging technologies in adaptive optics, energy conversion, and storage demand powerful design tools for nanophotonics. Phase, symmetry, and topology arising from quantum many-body effects are such powerful tools that bring a paradigm shift to nanophotonics. Here, we present two classes of nanophotonic devices based on quantum many-body systems. In the first case, non-Hermitian nanophotonic devices with non-trivial topology enable efficient solid-state energy conversion and thermal imaging. In the latter, light-matter interaction in a quantum material enables ultra-low power nonlinear optical devices. These approaches demonstrate how the new powerful design tools break many inherent trade-offs and pave the way for extreme nanophotonics.
Thermal radiation prompted the birth of quantum mechanics, and yet engineering thermal radiation has mostly remained in the classical realm. Quantum description of thermal light sources requires non-Hermitian description. Here, we develop a non-Hermitian description of nanoscale thermal emitters and demonstrate them using hybrid plasmonic and photonic metasurfaces. Our work shows that phase, symmetry, and topology, the new design tools offered by the quantum treatment relax the trade-offs between various performance parameters. We show selective thermal emitters with an emitter efficiency >80%. Such extreme-engineered nanophotonic devices alone enable applications such as flexible thermophotovoltaic energy conversion and we demonstrate it.
The next-generation technology poised to revolutionize our society is 3D displays, and tunable nanophotonics is the key. Tunability in optical devices has been achieved in the past by many techniques including electrical doping, chemical doping, mechanical actuation, and optical nonlinearity. However, they all present either fast and small or slow and large tuning response. An unconventional material that can exhibit a large tuning with MHz response is 1T-tantalum disulfide. We observed unity order refractive index change in the visible at room temperature with an in-plane DC bias, AC bias, and moderately intense white light illumination (2.5 Suns). The strong correlations in this material give rise to charge ordering even at room temperatures and result in the large tunability. Using this new optical material, we demonstrate tunable meta-devices operating in the visible.
The next-generation technology poised to revolutionize our society is 3D displays, and tunable nanophotonics is the key. Tunability in optical devices has been achieved in the past by many techniques including electrical doping, chemical doping, mechanical actuation, and optical nonlinearity. However, they all present either fast and small or slow and large tuning response. An unconventional material that can exhibit a large tuning with MHz response is 1T-tantalum disulfide. We observed unity order refractive index change in the visible at room temperature with an in-plane DC bias, AC bias, and moderately intense white light illumination (2.5 Suns). The strong correlations in this material give rise to charge ordering even at room temperatures and result in the large tunability. Using this new optical material, we demonstrate tunable meta-devices operating in the visible.
The two next-generation technologies poised to revolutionize our society are 3D displays and efficient energy conversion, and nanophotonics is the key to both. While tunable devices enable 3D displays, LiDAR, virtual reality, and such other applications, refractory nanophotonic devices enable efficient thermophotovoltaic energy conversion. Both of these nanophotonic devices can be realized by exploiting the phenomenon of many-body effects. While electronic correlation leads to a huge optical tunability, parity-time symmetric interaction between photonic resonators results in frequency-selective thermal emitters necessary for efficient thermophotovoltaics. This talk will describe tunable nanophotonic devices based on charge density waves in 1T-tantalum disulfide and frequency-selective thermal emitters based on hybrid plasmonic-photonic resonators.
Plasmon resonances in metallic nanoparticles result in enhanced light absorption and hot carrier generation. Although hot carriers are short-lived, their energy can be extracted in optical form resulting in photon upconversion. Two low energy photons absorbed by a plasmonic nanostructure, create a hot electron and a hot hole. These hot carriers get injected into an adjacent semiconductor quantum well where they radiatively recombine to emit a higher energy photon resulting in photon upconversion. This process involves injection of an electron and a hole across the same interface making it charge neutral. The upconversion emission has a linear dependence on the incident light intensity, making it promising for applications requiring low power operation. Theoretical studies show that a silver/semiconductor system can have an ideal efficiency of 25%.
Our experimental demonstration of this new scheme utilizes GaN/InGaN quantum wells decorated with both silver and gold. The use of two metals reduces band-bending in the semiconductor. Illuminating the sample with light spanning wavelengths of 500-540 nm produces upconversion photoluminescence centered at 435 nm. Control samples including undecorated quantum wells and metal nanostructures on a glass substrate do not show any upconversion ruling out possibilities of upconversion in individual materials. Further, the linear dependence of the upconverted light intensity with incident intensity rules out any non-linear or Auger mediated mechanisms. We will describe how this hot carrier upconversion process promises to be broadband, tunable, and more efficient than existing solid-state upconversion schemes, and discuss potential applications in solar energy, security, and photodetection applications.
The pulsed laser deposited nanocrystalline ZnO films doped by Ga up to six weight percent are studied by X-ray
difraction and generalized spectro-ellipsometry. We report substantial atomic structure modification of heavy
Ga-doped ZnO resulted and a concentration dependent increase of inter-planar distance. Measured dielectric
function spectra show strong blue-shift of the samples studied. Equilibrium atomic configurations and electron
energy structure of ZnO containing defects (voids and Ga impurities) are studied by the density functional theory
(DFT) and generalized gradient approximation (GGA). Atomic geometries are obtained from the total energy
minimization method. Optical functions are calculated within the random phase approximation including the
quasi-particles corrections and plasma excitation effects. We report energetically favorable paths of the voids
growth and aggregation in ZnO. Comparative analysis of experimental and theoretical results indicate that
measured blue-shift in ZnO:Ga substantially exceeds the Burstein-Moss shift as used in many previous work to
interpret concentration dependence of optical functions in heavy doped ZnO. We demonstrate that additional
mechanisms, such as structural and alloying effect, should be involved for quantitative interpretation of optics
of the nano-crystalline heavy-doped ZnO films.
Plasmonic materials have conventionally been gold and silver in optical frequencies. However, these conventional
metals in the near-infrared (NIR) and visible spectral ranges suffer from problems such as large losses. With
the advent of metamaterials, these metals pose a serious bottle-neck in the performances of metamaterial-based
devices not only due to the large losses associated with them in the NIR and visible wavelengths, but also their
magnitudes of real permittivity are too large. Both of these problems could be solved by using semiconductors
as plasmonic materials. Heavily doped zinc oxide and indium oxide can exhibit losses that are nearly four times
smaller than silver at the telecommunication wavelength with small negative real permittivity. In this paper, we
present the development of a low loss semiconductor plasmonic material, aluminum doped zinc oxide (AZO).
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.