The nitrogen vacancy (NV) center is the most widely studied single optical defect in diamond with great potential for applications in quantum technologies. Development of practical single-photon devices requires an understanding of the emission under a range of conditions and environments. In this work, we study the properties of a single NV center in nanodiamonds embedded in an air-like silica aerogel environment which provides a new domain for probing the emission behavior of NV centers in nanoscale environments. In this arrangement, the emission rate is governed primarily by the diamond crystal lattice with negligible contribution from the surrounding environment. This is in contrast to the conventional approach of studying nanodiamonds on a glass coverslip. We observe an increase in the mean lifetime due to the absence of a dielectric interface near the emitting dipoles and a distribution arising from the irregularities in the nanodiamond geometry. Our approach results in the estimation of the mean quantum efficiency (~0.7) of the nanodiamond NV emitters.
This is the post-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2011 ElsevierWhen developing sustainable building fabric technologies, it is essential that the energy use and CO2 burden arising from manufacture does not outweigh the respective in-use savings. This study investigates this paradigm by carrying out a streamlined life cycle assessment (LCA) of silica aerogel. This unique, nanoporous translucent insulation material has the lowest thermal conductivity of any solid, retaining up to four times as much heat as conventional insulation, whilst being highly transparent to light and solar radiation. Monolithic silica aerogel has been cited as the ‘holy grail’ of future glazing technology. Alternatively, translucent granular aerogel is now being produced on a commercial scale. In each case, many solvents are used in production, often accompanied by intensive drying processes, which may consume large amounts of energy and CO2. To date, there has been no peer-reviewed LCA of this material conducted to the ISO 14000 standard. Primary data for this ‘cradle-to-factory gate’ LCA is collected for silica aerogel made by low and high temperature supercritical drying. In both cases, the mass of raw materials and electricity usage for each process is monitored to determine the total energy use and CO2 burden. Findings are compared against the predicted operational savings arising from retrofitting translucent silica aerogel to a single glazed window to upgrade its thermal performance. Results should be treated as a conservative estimate as the aerogel is produced in a laboratory, which has not been developed for mass manufacture or refined to reduce its environmental impact. Furthermore, the samples are small and assumptions to upscale the manufacturing volume occur without major changes to production steps or equipment used. Despite this, parity between the CO2 burden and CO2 savings is achieved in less than 2 years, indicating that silica aerogel can provide a measurable environmental benefit.This work is funded by the EPSRC, Brunel University and Buro Happold Ltd, the University of Bath is funded by the EPSRC grant EP/F018622/1
Nanofibres, optical fibres narrower than the wavelength of light, degrade in hours on exposure to air. We show that encapsulation in hydrophobic silica aerogel (refractive index 1.05) provides protection and stability (over 2 months) without sacrificing low attenuation, strong confinement and accessible evanescent field. The measured attenuation was <0.03 dB/mm, over 10 × lower than reported with other encapsulants. This enables many nanofibre applications based on their extreme small size and strong external evanescent field, such as optical sensors, nonlinear optics, nanofibre circuits and high-Q resonators. The aerogel is more than a waterproof box, it is a completely-compatible gas-permeable material in intimate contact with the nanofibre and hydrophobic on both the macroscopic and molecular scales. Its benefits are illustrated by experiments on gas sensing (exploiting the aerogel's porosity) and supercontinuum generation (exploiting its ultra-low index).
Gas-filled hollow optical fiber references based on the P(13) transition of the ν1+ν3 band of 12C2H2 promise portability with moderate accuracy and stability. Previous realizations are corrected (<1σ) by using proper modeling of a shift due to line-shape. To improve portability, a sealed photonic microcell is characterized on the 12C2H2 ν1+ν3 P(23) transition with somewhat reduced accuracy and stability. Effects of the photonic crystal fiber, including surface modes, are explored. Both polarization-maintaining (PM) and non-PM 7-cell photonic bandgap fiber are shown to be unsuitable for kilohertz-level frequency references.
We have embedded thin tapered fibers (with diameters down to 1 microm) in silica aerogel with low loss. The aerogel is rigid but behaves refractively like air, protecting the taper without disturbing light propagation along it. This enables a new class of fiber devices exploiting volume evanescent interactions with the aerogel itself or with dopants or gases in the pores.
We derive solutions for radially polarized Bessel-Gauss beams in free-space by superimposing decentered Gaussian beams with differing polarization states. We numerically show that the analytical result is applicable even for large semi-aperture angles, and we experimentally confirm the analytical expression by employing a fiber-based mode-converter.
A method for making aerogel doped with gold nanoparticles (GNPs) produces a composite material with a well-defined localized surface plasmon resonance peak at 520 nm. The width of the extinction feature indicates the GNPs are well dispersed in the aerogel, making it suited to optical study. A simple effective medium approximation cannot explain the peak extinction wavelengths. The plasmonic field extends on a scale where aerogel cannot be considered isotropic, so a new model is required: a 5 nm glass coating on the GNPs models the extinction spectrum of the composite material, with air (aerogel), methanol (alcogel), or toluene filling the pores.
Plasmonic aerogel containing 50 nm gold nanoparticles is made using a modified 2-step method that maintains control over the gel time while preventing nanoparticle aggregation. Strong narrow surface plasmon resonances verify that the nanoparticles are well dispersed within the silica matrix, and enable applications in sensing, SERS, nonlinear optics or plasmonic gain. Discrepancies between measured and simulated resonance wavelengths are attributed to the breakdown of the effective index approximation, due to the short-scale penetration of the resonance electric field into the host medium.
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