41 research outputs found
Vibrationally coherent crossing and coupling of electronic states during internal conversion in beta-carotene
Coupling of nuclear and electronic degrees of freedom mediates energy flow in
molecules after optical excitation. The associated coherent dynamics in
polyatomic systems, however, remain experimentally unexplored. Here, we
combined transient absorption spectroscopy with electronic population control
to reveal nuclear wavepacket dynamics during the S2-S1 internal conversion in
beta-carotene. We show that passage through a conical intersection is
vibrationally coherent and thereby provides direct feedback on the role of
different vibrational coordinates in the breakdown of the Born-Oppenheimer
approximation
Sub-10 fs pulses tunable from 480 to 980 nm from a NOPA pumped by a Yb:KGW source
We describe two noncollinear optical parametric amplifier (NOPA) systems
pumped by either the second (515 nm) or the third (343 nm) harmonic of an
Yb:KGW amplifier, respectively. Pulse durations as short as 6.8 fs are readily
obtained by compression with commercially available chirped mirrors. The
availability of both second and third harmonic for NOPA pumping allows for
gap-free tuning from 520 to 980 nm. The use of an intermediate NOPA to generate
seed light at 780 nm extends the tuning range of the third-harmonic pumped NOPA
towards 450 nm
Ultrasensitive Label-Free Nanosensing and High-Speed Tracking of Single Proteins
: Label-free detection, analysis, and rapid tracking
of nanoparticles is crucial for future ultrasensitive sensing
applications, ranging from understanding of biological
interactions to the study of size-dependent classical-quantum
transitions. Yet optical techniques to distinguish nanoparticles
directly among their background remain challenging. Here we
present amplified interferometric scattering microscopy (aiSCAT)
as a new all-optical method capable of detecting
individual nanoparticles as small as 15 kDa proteins that is
equivalent to half a GFP. By balancing scattering and reflection
amplitudes the interference contrast of the nanoparticle signal
is amplified 1 to 2 orders of magnitude. Beyond high
sensitivity, a-iSCAT allows high-speed image acquisition exceeding several hundreds of frames-per-second. We showcase the
performance of our approach by detecting single Streptavidin binding events and by tracking single Ferritin proteins at 400
frames-per-second with 12 nm localization precision over seconds. Moreover, due to its extremely simple experimental
realization, this advancement finally enables a cheap and routine implementation of label-free all-optical single nanoparticle
detection platforms with sensitivity operating at the single protein level.Peer ReviewedPostprint (author's final draft
Direct observation of the coherent nuclear response after the absorption of a photon
How molecules convert light energy to perform a specific transformation is a
fundamental question in photophysics. Ultrafast spectroscopy reveals the
kinetics associated with electronic energy flow, but little is known about how
absorbed photon energy drives nuclear or electronic motion. Here, we used
ultrabroadband transient absorption spectroscopy to monitor coherent
vibrational energy flow after photoexcitation of the retinal chromophore. In
the proton pump bacteriorhodopsin we observed coherent activation of hydrogen
wagging and backbone torsional modes that were replaced by unreactive
coordinates in the solution environment, concomitant with a deactivation of the
reactive relaxation pathway
Control of Vibronic Transition Rates by Resonant Single-Molecule-Nanoantenna Coupling
Plasmonic nanostructures dramatically alter the radiative and nonradiative properties of single molecules in their vicinity. This coupling-induced change in decay channels selectively enhances specific vibronic transitions, which can enable plasmonic control of molecular reactivity. Here, we report coupling-dependent spectral emission shaping of single Rhodamine 800 molecules in the vicinity of plasmonic gold nanorods. We show that the relative vibronic transition rates of the first two vibronic transitions of the spontaneous emission spectrum can be tuned in the weak coupling regime, by approximately 25-fold, on the single molecule level.Peer ReviewedPostprint (author's final draft
Isolating strong nanoantenna-molecule interactions by ensemble-level single-molecule detection
Traditionally, the nanoscale interaction between single photon emitters and plasmonic nanostructures is studied by relying on deterministic, near-perfect, nanoscale-control, either top-down or bottom-up. However, these approaches are ultra-low throughput thus rendering systematic studies difficult and time-consuming. Here, we show a highly parallelised far-field tactic, combining multiplexed super-resolution fluorescence localization microscopy and data-driven statistical analysis, to study near-field interactions between gold nanorods and single molecules, even at bulk concentrations. We demonstrate that ensemble-level single molecule detection allows separating individual emitters according to their coupling strength with tailored resonant structures, which ultimately permits the reconstruction of super-resolved 2D interaction maps around individual nanoantennas.Peer ReviewedPostprint (author's final draft
Surface-Enhanced Raman Scattering Holography
Nanometric probes based on surface-enhanced Raman scattering (SERS) are promising candidates for all-optical environmental, biological and technological sensing applications with intrinsic quantitative molecular specificity. However, the effectiveness of SERS probes depends on a delicate trade-off between particle size, stability and brightness that has so far hindered their wide application in SERS imaging methodologies. In this Article, we introduce holographic Raman microscopy, which allows single-shot three-dimensional single-particle localization. We validate our approach by simultaneously performing Fourier transform Raman spectroscopy of individual SERS nanoparticles and Raman holography, using shearing interferometry to extract both the phase and the amplitude of wide-field Raman images and ultimately localize and track single SERS nanoparticles inside living cells in three dimensions. Our results represent a step towards multiplexed single-shot three-dimensional concentration mapping in many different scenarios, including live cell and tissue interrogation and complex anti-counterfeiting applications.Peer ReviewedPostprint (author's final draft
Widefield phototransient imaging for visualizing 3D motion of resonant particles in scattering environments
: Identifying, visualising and ultimately tracking dynamically moving non-fluorescent nanoparticles in the presence of non-specific scattering is a long-standing challenge across the nano- and life-sciences. In this work we demonstrate that our recently developed ultrafast holographic transient (UHT) microscope is ideally suited for meeting this challenge. We show that UHT microscopy allows reliably distinguishing off-resonant, dielectric, from resonant, metallic, nanoparticles, based on the phototransient signal: a pre-requisite for single-particle tracking in scattering environments. We then demonstrate the capability of UHT microscopy to holographically localize in 3D single particles over large volumes of view. Ultimately, we combine the two concepts to simultaneously track several tens of freely diffusing gold nanoparticles, within a 110 Ă— 110 Ă— 110 ÎĽm volume of view at an integration time of 10 ms per frame, while simultaneously recording their phototransient signals. The combined experimental concepts outlined and validated in this work lay the foundation for background-free 3D single-particle tracking applications or spectroscopy in scattering environments and are immediately applicable to systems as diverse as live cells and tissues or supported heterogeneous catalysts