317 research outputs found
Efficient Generation of Two-Photon Excited Phosphorescence from Molecules in Plasmonic Nanocavities.
Nonlinear molecular interactions with optical fields produce intriguing optical phenomena and applications ranging from color generation to biomedical imaging and sensing. The nonlinear cross-section of dielectric materials is low and therefore for effective utilisation, the optical fields need to be amplified. Here, we demonstrate that two-photon absorption can be enhanced by 108 inside individual plasmonic nanocavities containing emitters sandwiched between a gold nanoparticle and a gold film. This enhancement results from the high field strengths confined in the nanogap, thus enhancing nonlinear interactions with the emitters. We further investigate the parameters that determine the enhancement including the cavity spectral position and excitation wavelength. Moreover, the Purcell effect drastically reduces the emission lifetime from 520 ns to <200 ps, turning inefficient phosphorescent emitters into an ultrafast light source. Our results provide an understanding of enhanced two-photon-excited emission, allowing for optimization of efficient nonlinear light-matter interactions at the nanoscale
Accelerated Molecular Vibrational Decay and Suppressed Electronic Nonlinearities in Plasmonic Cavities through Coherent Raman Scattering
Molecular vibrations and their dynamics are of outstanding importance for
electronic and thermal transport in nanoscale devices as well as for molecular
catalysis. The vibrational dynamics of <100 molecules are studied through
three-colour time-resolved coherent anti-Stokes Raman spectroscopy (trCARS)
using plasmonic nanoantennas. This isolates molecular signals from four-wave
mixing (FWM), while using exceptionally low nanowatt powers to avoid molecular
damage via single-photon lock-in detection. FWM is found to be strongly
suppressed in nm-wide plasmonic gaps compared to plasmonic nanoparticles. The
ultrafast vibrational decay rates of biphenyl-4-thiol molecules are accelerated
ten-fold by a transient rise in local non-equilibrium temperature excited by
enhanced, pulsed optical fields within these plasmonic nanocavities. Separating
the contributions of vibrational population decay and dephasing carefully
explores the vibrational decay channels of these tightly confined molecules.
Such extreme plasmonic enhancement within nanogaps opens up prospects for
measuring single-molecule vibrationally-coupled dynamics and diverse molecular
optomechanics phenomena
Nanoscopy through a plasmonic nanolens.
Plasmonics now delivers sensors capable of detecting single molecules. The emission enhancements and nanometer-scale optical confinement achieved by these metallic nanostructures vastly increase spectroscopic sensitivity, enabling real-time tracking. However, the interaction of light with such nanostructures typically loses all information about the spatial location of molecules within a plasmonic hot spot. Here, we show that ultrathin plasmonic nanogaps support complete mode sets which strongly influence the far-field emission patterns of embedded emitters and allow the reconstruction of dipole positions with 1-nm precision. Emitters in different locations radiate spots, rings, and askew halo images, arising from interference of 2 radiating antenna modes differently coupling light out of the nanogap, highlighting the imaging potential of these plasmonic "crystal balls." Emitters at the center are now found to live indefinitely, because they radiate so rapidly.We acknowledge EPSRC grants EP/N016920/1, EP/L027151/1, and NanoDTC EP/L015978/1. OSO acknowledges support of Rubicon fellowship from the Netherlands Organisation for Scientific Research, and RC thanks support from Trinity College Cambridge
A Search for Variability in Exoplanet Analogues and Low-Gravity Brown Dwarfs
We report the results of a -band survey for photometric variability in a
sample of young, low-gravity objects using the New Technology Telescope (NTT)
and the United Kingdom InfraRed Telescope (UKIRT). Surface gravity is a key
parameter in the atmospheric properties of brown dwarfs and this is the first
large survey that aims to test the gravity dependence of variability
properties. We do a full analysis of the spectral signatures of youth and
assess the group membership probability of each target using membership tools
from the literature. This results in a 30 object sample of young low-gravity
brown dwarfs. Since we are lacking in objects with spectral types later than
L9, we focus our statistical analysis on the L0-L8.5 objects. We find that the
variability occurrence rate of L0-L8.5 low-gravity brown dwarfs in this survey
is . We reanalyse the results of Radigan 2014 and find that
the field dwarfs with spectral types L0-L8.5 have a variability occurrence rate
of . We determine a probability of that the samples are
drawn from different distributions. This is the first quantitative indication
that the low-gravity objects are more likely to be variable than the field
dwarf population. Furthermore, we present follow-up and
observations of the young, planetary-mass variable object PSO 318.5-22 over
three consecutive nights. We find no evidence of phase shifts between the
and bands and find higher amplitudes. We use the lightcurves
to measure a rotational period of hr for PSO 318.5-22.Comment: accepted for publication in MNRA
BDSIM: An Accelerator Tracking Code with Particle-Matter Interactions
Beam Delivery Simulation (BDSIM) is a program that simulates the passage of
particles in a particle accelerator. It uses a suite of standard high energy
physics codes (Geant4, ROOT and CLHEP) to create a computational model of a
particle accelerator that combines accurate accelerator tracking routines with
all of the physics processes of particles in Geant4. This unique combination
permits radiation and detector background simulations in accelerators where
both accurate tracking of all particles is required over long range or over
many revolutions of a circular machine, as well as interaction with the
material of the accelerator.Comment: 20 pages, 17 figures. Accepted for publication 28th Jan 202
Room-Temperature Optical Picocavities below 1 nm3 Accessing Single-Atom Geometries.
Reproducible confinement of light on the nanoscale is essential for the ability to observe and control chemical reactions at the single-molecule level. Here we reliably form millions of identical nanocavities and show that the light can be further focused down to the subnanometer scale via the creation of picocavities, single-adatom protrusions with angstrom-level resolution. For the first time, we stabilize and analyze these cavities at room temperatures through high-speed surface-enhanced Raman spectroscopy on specifically selected molecular components, collecting and analyzing more than 2 million spectra. Data obtained on these picocavities allows us to deduce structural information on the nanoscale, showing that thiol binding to gold destabilizes the metal surface to optical irradiation. Nitrile moieties are found to stabilize picocavities by 10-fold against their disappearance, typically surviving for >1 s. Such constructs demonstrate the accessibility of single-molecule chemistry under ambient conditions
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