Publications
179 results found
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
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.
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.
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
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.
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: 2
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: 3
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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- Citations: 10
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.
Azzam S, Kildishev A, Ma R-M, et al., 2020, Ten years of spasers and plasmonic nanolasers, LIGHT-SCIENCE & APPLICATIONS, Vol: 9, ISSN: 2047-7538
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- Citations: 125
Gusken NA, Nielsen MP, Nguyen NB, et al., 2020, Efficient Four Wave Mixing and Low-Loss Adiabatic In-Coupling in Hybrid Gap Plasmonic Waveguides, ISSN: 1092-8081
We show four-wave-mixing over 2 μm with 1% signal-to-idler conversion efficiency enabled by strong non-linearities and highly confined fields. We also demonstrate low-loss in-coupling into nanometer gaps with an efficiency of 80%.
Doiron B, Gusken NA, Lauri A, et al., 2020, Hot Carrier Optoelectronics with Titanium Nitride, Lasers and Electro-Optics Society Annual Meeting-LEOS, ISSN: 1092-8081
© 2020 OSA. Titanium oxynitride enables a range of plasmonic and optoelectronic functionality using long-lived photo-generated hot carriers. We explore the time scale of hot carriers in TiN and their use in photochemical reduction and Schottky detectors.
Marques Rodrigues J, Walker BT, Dhar HS, et al., 2020, Non-stationary statistics and formation jitter in transient photon condensation, Nature Communications, Vol: 11, ISSN: 2041-1723
While equilibrium phase transitions are easily described by order parameters and free-energylandscapes, for their non-stationary counterparts these quantities are usually ill-defined. Here,we probe transient non-equilibrium dynamics of an optically pumped, dye-filled microcavity. Wequench the system to a far-from-equilibrium state and find delayed condensation close to a criticalexcitation energy, a transient equivalent of critical slowing down. Besides number fluctuations nearthe critical excitation energy, we show that transient phase transitions exhibit timing jitter in thecondensate formation. This jitter is a manifestation of the randomness associated with spontaneousemission, showing that condensation is a stochastic, rather than deterministic process. Despite thenon-equilibrium character of this phase transition, we construct an effective free-energy landscapethat describes the formation jitter and allows, in principle, its generalization to a wider class ofprocesses.
Walker BT, Rodrigues JD, Dhar HS, et al., 2020, Non-stationary statistics and formation jitter in transient photon condensation, Publisher: NATURE PUBLISHING GROUP
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- Citations: 8
Gusken NA, Nielsen MP, Nguyen NB, et al., 2020, Efficient four wave mixing and low-loss adiabatic in-coupling in hybrid gap plasmonic waveguides, Conference on Lasers and Electro-Optics (CLEO), Publisher: IEEE, ISSN: 2160-9020
Gennaro SD, Li Y, Maier SA, et al., 2020, Mixed order nonlinear processes from metasurfaces of multi-resonant gold antennas, Conference on Lasers and Electro-Optics (CLEO), Publisher: IEEE, ISSN: 2160-9020
Gennaro SD, Li Y, Maier SA, et al., 2020, Nonlinear Geometric Phase Gradient Metasurface beyond the Dipole Approximation, Conference on Lasers and Electro-Optics (CLEO), Publisher: IEEE, ISSN: 2160-9020
Güsken NA, Nielsen MP, Nguyen NB, et al., 2020, Efficient four wave mixing and low-loss adiabatic in-coupling in hybrid gap plasmonic waveguides
We show four-wave-mixing over 2 µm with 1% signal-to-idler conversion efficiency enabled by strong non-linearities and highly confined fields. We also demonstrate low-loss in-coupling into nanometer gaps with an efficiency of 80%.
Doiron B, Güsken NA, Lauri A, et al., 2020, Hot carrier optoelectronics with titanium nitride
Titanium oxynitride enables a range of plasmonic and optoelectronic functionality using long-lived photo-generated hot carriers. We explore the time scale of hot carriers in TiN and their use in photochemical reduction and Schottky detectors.
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