Publications
187 results found
Xu J, Fu M, Ji C, et al., 2023, Plasmonic‐enhanced NIR‐II downconversion fluorescence beyond 1500 nm from core–shell–shell lanthanide nanoparticles, Advanced Optical Materials, Vol: 11, ISSN: 2195-1071
This paper reports on the light amplification of NaGdF4:Yb,Er,Ce@NaGdF4:Yb,Nd@NaGdF4 core–shell–shell downconversion nanoparticles (CSS-DCNPs) in the near-infrared second biological window (NIR-II: 1000–1700 nm) by plasmonic nanostructures. Through a precisely controlled plasmonic metallic nanostructure, fluorescence from Yb3+ induced 1000 nm emission, Nd3+ induced 1060 nm emission, and Er3+ induced 1527 nm emission are enhanced 1.6-fold, 1.7-fold, and 2.2-fold, respectively, under an 808 nm laser excitation for the CSS-DCNPs coupled with a gold hole-cap nanoarray (Au-HCNA), while the Er3+ induced 1527 nm emission under a 980 nm laser excitation is enhanced up to 6-fold. To gain insight into the enhancement mechanism, the plasmonic modulation of Er3+ induced NIR-II emission at 1550 nm under 980 nm excitation is studied by FDTD simulation and lifetime measurements, showing the observed fluorescence enhancement can be attributed to a combination of enhanced excitation and an increased radiative decay rate.
Ma Y, Gemmell N, Pearce E, et al., 2023, Eliminating thermal infrared background noise by imaging with undetected photons, Physical Review A: Atomic, Molecular and Optical Physics, Vol: 108, ISSN: 1050-2947
Spectroscopy and imaging in the mid-infrared (2.5µm∼λ∼25µm) is bedeviled by the presence of a strong 300-K thermal background at room temperature that makes infrared (IR) detectors decades noisier than can be readily achieved in the visible. The technique of imaging with undetected photons (IUP) exploits the quantum correlations between entangled photon pairs to transfer image information from one spectral region to another, and here we show that it does so in a way that is immune to the thermal background. This means that IUP can be used to perform high-speed photon-counting measurements across the mid-IR spectrum, using uncooled visible detectors that are many times cheaper, faster, and more sensitive than their IR counterparts.
Yao Q, Berenov AVV, Bower R, et al., 2023, Crystalline AuNP-Decorated Strontium Niobate Thin Films: Strain-Controlled AuNP Morphologies and Optical Properties for Plasmonic Applications, ACS APPLIED NANO MATERIALS, Vol: 6, Pages: 11115-11123
Doiron B, Li Y, Bower R, et al., 2023, Optimizing hot electron harvesting at planar metal–semiconductor interfaces with titanium oxynitride thin films, ACS Applied Materials and Interfaces, Vol: 25, Pages: 30417-30426, ISSN: 1944-8244
Understanding metal-semiconductor interfaces is critical to the advancement of photocatalysis and sub-bandgap solar energy harvesting where electrons in the metal can be excited by sub-bandgap photons and extracted into the semiconductor. In this work, we compare the electron extraction efficiency across Au/TiO2 and titanium oxynitride (TiON)/TiO2-x interfaces, where in the latter case the spontaneously forming oxide layer (TiO2-x) creates a metal-semiconductor contact. Time-resolved pump-probe spectroscopy is used to study the electron recombination rates in both cases. Unlike the nanosecond recombination lifetimes in Au/TiO2, we find a bottleneck in the electron relaxation in the TiON system, which we explain using a trap-mediated recombination model. Using this model, we investigate the tunability of the relaxation dynamics with oxygen content in the parent film. The optimized film (TiO0.5N0.5) exhibits the highest carrier extraction efficiency (NFC ≈ 2.8 × 1019 m-3), slowest trapping, and an appreciable hot electron population reaching the surface oxide (NHE ≈ 1.6 × 1018 m-3). Our results demonstrate the productive role oxygen can play in enhancing electron harvesting and prolonging electron lifetimes, providing an optimized metal-semiconductor interface using only the native oxide of titanium oxynitride.
Oulton R, 2023, Emission enhancement of erbium in a reverse nanofocusing waveguide, Nature Communications, Vol: 14, Pages: 1-10, ISSN: 2041-1723
Since Purcell’s seminal report 75 years ago, electromagnetic resonators have been used to control light-matter interactions to make brighter radiation sources and unleash unprecedented control over quantum states of light and matter. Indeed, optical resonators such as microcavities and plasmonic antennas offer excellent control but only over a limited spectral range. Strategies to mutually tune and match emission and resonator frequency are often required, which is intricate and precludes the possibility of enhancing multiple transitions simultaneously. In this letter, we report a strong radiative emission rate enhancement of Er3+-ions across the telecommunications C-band in a single plasmonic waveguide based on the Purcell effect. Our gap waveguide uses a reverse nanofocusing approach to efficiently enhance, extract and guide emission from the nanoscale to a photonic waveguide while keeping plasmonic losses at a minimum. Remarkably, the large and broadband Purcell enhancement allows us to resolve Stark-split electric dipole transitions, which are typically only observed under cryogenic conditions. Simultaneous radiative emission enhancement of multiple quantum states is of great interest for photonic quantum networks and on-chip data communications.
Gemmell NR, Florez J, Pearce E, et al., 2023, Loss-compensated and enhanced midinfrared interaction-free sensing with undetected photons, Physical Review Applied, Vol: 19, ISSN: 2331-7019
Sensing with undetected photons enables the measurement of absorption and phase shifts at wavelengths different from those detected. Here, we experimentally map the balance and loss parameter space in a nondegenerate nonlinear interferometer, showing the recovery of sensitivity despite internal losses at the detection wavelength. We further explore an interaction-free operation mode with a detector-to-sample incident optical power ratio of over 200. This allows changes in attowatt levels of power at 3.4μm wavelength to be detected at 1550 nm, immune to the level of thermal black-body background. This reveals an ultrasensitive infrared imaging methodology capable of probing samples effectively “in the dark.”
Stenning KD, Xiao X, Holder HH, et al., 2023, Low-power continuous-wave all-optical magnetic switching in ferromagnetic nanoarrays, Cell Reports Physical Science, Vol: 4, Pages: 1-15, ISSN: 2666-3864
All-optical magnetic switching promises ultrafast magnetizationcontrol without a magnetic field. Existing schemes typically requirepower-hungry femtosecond-pulsed lasers and complex magneticmaterials. Here, we demonstrate deterministic, all-optical magneticswitching in simple ferromagnetic nanomagnets (Ni81Fe19, Ni50Fe50)with sub-diffraction limit dimensions using a focused low-power,linearly polarized continuous-wave laser. Isolated nanomagnetsare switched across a range of dimensions, laser wavelengths, andpowers. All square-geometry artificial spin ice vertex configurationsare written at low powers (2.74 mW). Usually, switching with linearlypolarized light is symmetry forbidden; here, the laser spot has asimilar size to the nanomagnets, producing an absorption distribution that depends on the nanoisland-spot displacement. We attribute the deterministic switching to the transient dynamics of thisasymmetric absorption. No switching is observed in Co or Ni nanostructures, suggesting the multi-species nature of NiFe plays a role.These results usher in inexpensive, low-power, optically controlleddevices with impact across data storage, neuromorphic computation, and reconfigurable magnonics.
Pearce E, Flórez J, Gemmell NR, et al., 2023, Enhancing Nonlinear Interferometers for Imaging with Undetected Photons: Seeding and High-Gain
Infrared (IR) imaging and spectroscopy is invaluable to many disciplines for its ability to probe molecular responses, from material analysis to diagnostic medicine. However, these applications are often limited by inefficient, noisy detectors. Non-degenerate nonlinear interferometers (NLIs) offer an alternative route through a technique known as imaging with undetected photons [1]. For an NLI producing visible-IR photon pairs, a change in the IR due to an object can be observed as a change to the interference of the visible photons. The IR does not need to be detected, bypassing the need for IR detectors completely.
Güsken NA, Fu M, Zapf M, et al., 2023, Emission enhancement of erbium in a reverse nanofocusing waveguide, Pages: 584-585
We report emission enhancement of Er3+-ions across the telecommunications C-band in a single plasmonic waveguide based on the Purcell effect. Our gap waveguide uses a reverse nanofocusing approach to efficiently enhance, extract and guide emission from the nanoscale to a photonic waveguide while keeping plasmonic losses at a minimum. A large and broadband Purcell enhancement allows us to resolve Stark-split electric dipole transitions. Simultaneous enhancement of multiple quantum states is of great interest for photonic and quantum networks.
Fu M, Mota MPDP, Xiao X, et al., 2023, Near unity Raman β-factor of surface enhanced Raman scattering in a waveguide, Pages: 1327-1328
We show that SERS from monolayer 4-Aminothiophenol (4-ATP) bonded to a plasmonic gap waveguide is directed into a single mode with >99% efficiency. Although sacrificing a confinement dimension, we find a 103 x SERS enhancement across a broad spectral range, enabled by the plasmonic waveguide9s larger sensing volume and non-resonant waveguide mode. Waveguide-SERS (W-SERS) is bright enough to image Raman transport across the waveguides. This exposes the roles of nanofocusing, the Purcell effect and the spontaneous Raman scattering factor, or Raman β-factor.
Ren T, Wang J, Kumar A, et al., 2022, Optical gain spectrum and confinement factor of a monolayer semiconductor in an ultrahigh quality cavity
<jats:title>Abstract</jats:title> <jats:p>Two-dimensional (2D) semiconductors have attracted great attention as a novel class of gain materials for low-threshold on-chip coherent light sources. Due to their atomically thin scale, these materials exhibit distinct gain characteristics and associated emitter-to-cavity coupling when integrated into a cavity. Despite several experimental reports on lasing, the underlying gain mechanism of 2D materials remains elusive due to a lack of key information, including modal gain and confinement factor. Here, we demonstrate a novel approach to directly determine the absorption coefficient of monolayer WS<jats:sub>2</jats:sub> by characterizing the whispering gallery modes in a van der Waals microdisk cavity. By exploiting the cavity’s high intrinsic quality factor of 2.5×10<jats:sup>4</jats:sup>, the absorption coefficient spectrum is experimentally resolved with unprecedented accuracy. We show that the excitonic gain signal and confinement factor can be assessed by analyzing the quality factors near the exciton resonance. The excitonic gain reduces the WS<jats:sub>2</jats:sub> absorption coefficient by 2×10<jats:sup>4</jats:sup> cm<jats:sup>− 1</jats:sup> at room temperature, indicating a local population inversion described in the excitonic two-band model. These results are essential for unveiling the gain mechanism in emergent low-threshold 2D-semiconductor-based laser devices.</jats:p>
Kinsler P, McCall MW, Oulton RF, et al., 2022, The surprising persistence of time-dependent quantum entanglement, New Journal of Physics, Vol: 24, Pages: 1-14, ISSN: 1367-2630
The mismatch between elegant theoretical models and the detailed experimental reality is particularly pronounced in quantum nonlinear interferometry (QNI). In stark contrast to theory, experiments contain pump beams that start in impure states and that are depleted, quantum noise that affects—and drives—any otherwise gradual build up of the signal and idler fields, and nonlinear materials that are far from ideal and have a complicated time-dependent dispersive response. Notably, we would normally expect group velocity mismatches to destroy any possibility of measurable or visible entanglement, even though it remains intact—the mismatches change the relative timings of induced signal–idler entanglements, thus generating 'which path' information. Using an approach based on the positive-P representation, which is ideally suited to such problems, we are able to keep detailed track of the time-domain entanglement crucial for QNI. This allows us to show that entanglement can be—and is—recoverable despite the obscuring effects of real-world complications; and that recovery is attributable to an implicit time-averaging present in the detection process.
Fu M, Mota MPDSP, Xiao X, et al., 2022, Near-unity Raman beta-factor of surface-enhanced Raman scattering in a waveguide, Nature Nanotechnology, Vol: 17, Pages: 1251-1257, ISSN: 1748-3387
The Raman scattering of light by molecular vibrations is a powerful technique to fingerprint molecules through their internal bonds and symmetries. Since Raman scattering is weak1, methods to enhance, direct and harness it are highly desirable, and this has been achieved using optical cavities2, waveguides3,4,5,6 and surface-enhanced Raman scattering (SERS)7,8,9. Although SERS offers dramatic enhancements2,6,10,11 by localizing light within vanishingly small hot-spots in metallic nanostructures, these tiny interaction volumes are only sensitive to a few molecules, yielding weak signals12. Here we show that SERS from 4-aminothiophenol molecules bonded to a plasmonic gap waveguide is directed into a single mode with >99% efficiency. Although sacrificing a confinement dimension, we find a SERS enhancement of ~103 times across a broad spectral range enabled by the waveguide’s larger sensing volume and non-resonant waveguide mode. Remarkably, this waveguide SERS is bright enough to image Raman transport across the waveguides, highlighting the role of nanofocusing13,14,15 and the Purcell effect16. By analogy to the β-factor from laser physics10,17,18,19,20, the near-unity Raman β-factor we observe exposes the SERS technique to alternative routes for controlling Raman scattering. The ability of waveguide SERS to direct Raman scattering is relevant to Raman sensors based on integrated photonics7,8,9 with applications in gas sensing and biosensing.
Oulton RF, Florez J, Clark AS, 2022, Ferroelectric nanosheets boost nonlinearity, NATURE PHOTONICS, Vol: 16, Pages: 611-612, ISSN: 1749-4885
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- Citations: 1
Güsken NA, Fu M, Zapf M, et al., 2022, Fluorescence enhancement of Er<sup>3+</sup>-ions using reverse hybrid plasmonic nano-focusing
We report the broadband fluorescence enhancement of erbium ions embedded in a single non-resonant reverse nano-focusing waveguide. We measure a large radiative Purcell enhancement of a total emission rate enhancement of > 250 across the entire measured spectrum including the prominent telecoms C-band. Further, we observe the enhancement of single electric dipole transitions from Stark-split levels at room temperature.
Güsken NA, Fu M, Zapf M, et al., 2022, Fluorescence enhancement of Er<sup>3+</sup>-ions using reverse hybrid plasmonic nano-focusing
We report the broadband fluorescence enhancement of erbium ions embedded in a single non-resonant reverse nano-focusing waveguide. We measure a large radiative Purcell enhancement of a total emission rate enhancement of > 250 across the entire measured spectrum including the prominent telecoms C-band. Further, we observe the enhancement of single electric dipole transitions from Stark-split levels at room temperature.
Fu M, Mota M, Xiao X, et al., 2022, Near unity Raman β-factor of surface enhanced Raman scattering in a waveguide
The Raman scattering of light by molecular vibrations offers a powerful technique to ‘fingerprint’ molecules via their internal bonds and symmetries. Since Raman scattering is weak 1 , methods to enhance, direct and harness it are highly desirable, e.g. through the use of optical cavities 2 , waveguides 3–6 , and surface enhanced Raman scattering (SERS) 7–9 . While SERS offers dramatic enhancements 6,15,22,2 by localizing light within vanishingly small ‘hot-spots’ in metallic nanostructures, these tiny interaction volumes are only sensitive to few molecules, yielding weak signals that are difficult to detect 10 . Here, we show that SERS from 4-Aminothiophenol (4-ATP) molecules bonded to a plasmonic gap waveguide is directed into a single mode with > 99% efficiency. Although sacrificing a confinement dimension, we find > 10 4 times SERS enhancement across a broad spectral range enabled by the waveguide’s larger sensing volume and non-resonant mode. Remarkably, the waveguide-SERS (W-SERS) is bright enough to image Raman transport across the waveguides exposing the roles of nanofocusing 11–13 and the Purcell effect 14 . Emulating the e-factor from laser physics 15–17 , the near unity Raman -factor observed exposes the SERS technique in a new light and points to alternative routes to controlling Raman scattering. The ability of W-SERS to direct Raman scattering is relevant to Raman sensors based on integrated photonics 7–9 with applications in gas and bio-sensing as well as healthcare.
Yang J, Dichtl P, Florez J, et al., 2022, Stimulated emission tomography analysis of plasmonic nanoantennas, Conference on Active Photonic Platforms held Part of SPIE Nanoscience and Engineering Conference, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
Bower R, Wells MP, Johnson F, et al., 2021, Tunable double epsilon-near-zero behavior in niobium oxynitride thin films, Applied Surface Science, Vol: 569, Pages: 150912-150912, ISSN: 0169-4332
Gennaro SD, Roschuk T, Maier SA, et al., 2021, Critical Coupling of a Single Metallic Nanoantenna under Focused Illumination
In this work, we investigate the critical coupling of a single gold disk antenna with a focused beam by evaluating its absorption and scattering using spectral interferometry microcopy.
Besteiro LV, Cortes E, Ishii S, et al., 2021, Hot electron physics and applications, JOURNAL OF APPLIED PHYSICS, Vol: 129, ISSN: 0021-8979
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- Citations: 3
Rodrigues JD, Dhar HS, Walker BT, et al., 2021, Learning the Fuzzy Phases of Small Photonic Condensates, PHYSICAL REVIEW LETTERS, Vol: 126, ISSN: 0031-9007
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- Citations: 4
Clark AS, Chekhova M, Matthews JCF, et al., 2021, Special Topic: Quantum sensing with correlated light sources, APPLIED PHYSICS LETTERS, Vol: 118, ISSN: 0003-6951
Gennaro SD, Roschuk T, Maier SA, et al., 2021, Critical Coupling of a Single Metallic Nanoantenna under Focused Illumination, Conference on Lasers and Electro-Optics (CLEO), Publisher: IEEE, ISSN: 2160-9020
Dhar HS, Rodrigues JD, Walker BT, et al., 2020, Transport and localization of light inside a dye-filled microcavity, Physical Review A: Atomic, Molecular and Optical Physics, Vol: 102, Pages: 1-9, ISSN: 1050-2947
The driven-dissipative nature of light-matter interaction inside a multimode, dye-filled microcavity makes it an ideal system to study nonequilibrium phenomena, such as transport. In this work, we investigate how light is efficiently transported inside such a microcavity, mediated by incoherent absorption and emission processes. In particular, we show that there exist two distinct regimes of transport, viz. conductive and localized, arising from the complex interplay between the thermalizing effect of the dye molecules and the nonequilibrium influence of driving and loss. The propagation of light in the conductive regime occurs when several localized cavity modes undergo dynamical phase transitions to a condensed, or lasing, state. Furthermore, we observe that, while such transport is robust for weak disorder in the cavity potential, strong disorder can lead to localization of light even under good thermalizing conditions. Importantly, the exhibited transport and localization of light is a manifestation of the nonequilibrium dynamics rather than any coherent interference in the system.
Pearce E, Phillips CC, Oulton RF, et al., 2020, Heralded spectroscopy with a fiber photon-pair source, Applied Physics Letters, Vol: 117, Pages: 1-6, ISSN: 0003-6951
The correlations between photons generated by nonlinear optical processes offer advantages for many quantum technology applications, including spectroscopy, imaging, and metrology. Here, we use spontaneous four-wave mixing in a birefringent single-mode fiber pumped by a tunable pulsed laser as a broadly tunable source of phase-matched non-degenerate photon pairs for spectroscopy. The pairs are tunable such that the idler beam measures the transmittance spectrum of a sample in the near infrared, while the visible signal beam independently reports correlation information. By the time-resolved counting of both signal and idler photons, we use photon-number correlations to remove uncorrelated noise from the probe beam. Here, we have used heralded spectroscopy to measure the absorption spectrum of gallium arsenide near its band edge, despite the idler photon spectrum being dominated by a large background from spontaneous Raman scattering.
Grinblat G, Zhang H, Nielsen MP, et al., 2020, Efficient ultrafast all-optical modulation in a nonlinear crystalline gallium phosphide nanodisk at the anapole excitation, Science Advances, Vol: 6, ISSN: 2375-2548
High–refractive index nanostructured dielectrics have the ability to locally enhance electromagnetic fields with low losses while presenting high third-order nonlinearities. In this work, we exploit these characteristics to achieve efficient ultrafast all-optical modulation in a crystalline gallium phosphide (GaP) nanoantenna through the optical Kerr effect (OKE) and two-photon absorption (TPA) in the visible/near-infrared range. We show that an individual GaP nanodisk can yield differential reflectivity modulations of up to ~40%, with characteristic modulation times between 14 and 66 fs, when probed at the anapole excitation (AE). Numerical simulations reveal that the AE represents a unique condition where both the OKE and TPA contribute with the same modulation sign, maximizing the response. These findings highly outperform previous reports on sub–100-fs all-optical switching from resonant nanoscale dielectrics, which have demonstrated modulation depths no larger than 0.5%, placing GaP nanoantennas as a promising choice for ultrafast all-optical modulation at the nanometer scale.
Sistani M, Bartmann MG, Gusken NA, et al., 2020, Plasmon-Driven Hot Electron Transfer at Atomically Sharp Metal-Semiconductor Nanojunctions, ACS PHOTONICS, Vol: 7, Pages: 1642-1648, ISSN: 2330-4022
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Sistani M, Bartmann MG, Gusken NA, et al., 2020, Stimulated raman scattering in Ge nanowires, The Journal of Physical Chemistry C: Energy Conversion and Storage, Optical and Electronic Devices, Interfaces, Nanomaterials, and Hard Matter, Vol: 124, Pages: 13872-13877, ISSN: 1932-7447
Investigating group-IV-based photonic components is a very active area of research with extensive interest in developing complementary metal-oxide-semiconductor (CMOS) compatible light sources. However, due to the indirect band gap of these materials, effective light-emitting diodes and lasers based on pure Ge or Si cannot be realized. In this context, there is considerable interest in developing group-IV based Raman lasers. Nevertheless, the low quantum yield of stimulated Raman scattering in Si and Ge requires large device footprints and high lasing thresholds. Consequently, the fabrication of integrated, energy-efficient Raman lasers is challenging. Here, we report the systematic investigation of stimulated Raman scattering (SRS) in Ge nanowires (NWs) and axial Al-Ge-Al NW heterostructures with Ge segments that come into contact with self-aligned Al leads with abrupt metal–semiconductor interfaces. Depending on their geometry, these quasi-one-dimensional (1D) heterostructures can reassemble into Ge nanowires, Ge nanodots, or Ge nanodiscs, which are monolithically integrated within monocrystalline Al (c-Al) mirrors that promote both optical confinement and effective heat dissipation. Optical mode resonances in these nanocavities support in SRS thresholds as low as 60 kW/cm2. Most notably, our findings provide a platform for elucidating the high potential of future monolithically integrated, nanoscale low-power group-IV-based Raman lasers.
Azzam SI, Kildishev AV, Ma R-M, et al., 2020, Ten years of spasers and plasmonic nanolasers., Light Sci Appl, Vol: 9
Ten years ago, three teams experimentally demonstrated the first spasers, or plasmonic nanolasers, after the spaser concept was first proposed theoretically in 2003. An overview of the significant progress achieved over the last 10 years is presented here, together with the original context of and motivations for this research. After a general introduction, we first summarize the fundamental properties of spasers and discuss the major motivations that led to the first demonstrations of spasers and nanolasers. This is followed by an overview of crucial technological progress, including lasing threshold reduction, dynamic modulation, room-temperature operation, electrical injection, the control and improvement of spasers, the array operation of spasers, and selected applications of single-particle spasers. Research prospects are presented in relation to several directions of development, including further miniaturization, the relationship with Bose-Einstein condensation, novel spaser-based interconnects, and other features of spasers and plasmonic lasers that have yet to be realized or challenges that are still to be overcome.
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