7 research outputs found
Enhanced-Resolution Single-Shot 2DFT Spectroscopy by Spatial Spectral Interferometry
We demonstrate use of spatial interference for the complete electric field reconstruction of two-dimensional (2D) coherent spectroscopic signals generated through four-wave mixing (4WM) in a single laser shot. Until now, the amplitude and phase characterization of 4WM signals has relied primarily on Fourier transform spectral interferometry (FTSI), which limits the measurement’s sensitivity and resolution. We show that spatial spectral interferometry (SSI) is a generalized approach to 4WM signal detection that eliminates these inherent limitations of FTSI without introducing additional experimental complexity. SSI is used to measure the 2D photon echo spectra of two systems with dramatically different line widths, the coupled D line transitions in rubidium vapor and the energy-transfer dynamics in the light-harvesting protein LH2
Isolated Ground-State Vibrational Coherence Measured by Fifth-Order Single-Shot Two-Dimensional Electronic Spectroscopy
Vibrations play a critical role in
many photochemical and photophysical
processes in which excitations reside on the electronically excited
state. However, difficulty in assigning signals from spectroscopic
measurements uniquely to a specific electronic state, ground or otherwise,
has exposed limitations to their physical interpretation. Here, we
demonstrate the selective excitation of vibrational coherences on
the ground electronic state through impulsive Raman scattering, whose
weak fifth-order signal is resonantly enhanced by coupling to strong
electronic transitions. The six-wave mixing signals measured using
this technique are free of lower-order cascades and represent correlations
between zero-quantum vibrational coherences in the ground state and
single-quantum coherences between the ground and electronic states.
We believe that this technique has the potential to shed much-needed
insight onto some of the mysteries regarding the origin of long-lived
coherences observed in photosynthetic and other coupled chromophore
systems
Dissecting Hidden Couplings Using Fifth-Order Three-Dimensional Electronic Spectroscopy
We report the demonstration of single-quantum 3D electronic spectroscopy. Utilizing the recently introduced gradient assisted photon echo (GRAPE) methodology, the fifth-order nonlinear polarization of the solvatochromatic dye IR144 corresponding to evolution through three sequential single-quantum coherences is measured. GRAPE, which allows a 2D slice of data to be acquired in parallel, permits a practical implementation of 3D spectroscopy at optical frequencies in a matter of minutes instead of hours. By spreading frequencies into a third spectral dimension, we can resolve features in the spectra that are otherwise obscured. For IR144, a previously unresolved cross peak originating from high frequency vibronic modes is observed in the spectrum. Theoretical modeling based on the cumulant expansion truncated at second order reproduces the main features of the experimental results. This experimental approach will enable further high dimensional spectroscopic experiments
Exciton–Phonon Spectroscopy of Quantum Dots Below the Single-Particle Homogeneous Line Width
We
demonstrate that high-dimensionality coherent spectroscopy yields
“super-resolved” spectra whereby peaks may be localized
far below their homogeneous line width by resolving them across multiple,
coherently coupled dimensions. We implement this technique using a
fifth-order photon-echo spectroscopy called Gradient-Assisted Multidimensional
Electronic–Raman Spectroscopy (GAMERS) that combines resonant
and nonresonant excitation to disperse the optical response across
three spectral dimensions: two involving excitonic transitions and
one that encodes phonon energies. In analogy to super-resolution localization
microscopies, which separate spatially overlapping signals in time,
GAMERS isolates signals spectrally using combined electronic and nuclear
resolution. Optical phonon lines in a colloidal solution of CdSe quantum
dots at room temperature separated by less than 150 ÎĽeV are
resolved despite the homogeneous line width of these transitions being
nearly an order of magnitude broader. The frequency difference between
these phonon modes is attributed to softening of the longitudinal
phonon mode upon excitation to the lowest exciton state. Further,
such phonon mode selectivity yields spectra with electronic line widths
that approach the single particle limit. Through this enhanced spectral
resolution, the GAMERS method yields insights into the nature of coupling
between longitudinal optical and acoustic phonons and specific excitonic
transitions that were previously hidden
Ultrafast Imaging of Carrier Cooling in Metal Halide Perovskite Thin Films
Understanding carrier
relaxation in lead halide perovskites at
the nanoscale is critical for advancing their device physics. Here,
we directly image carrier cooling in polycrystalline CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> films with nanometer spatial resolution.
We observe that upon photon absorption, highly energetic carriers
rapidly thermalize with the lattice at different rates across the
film. The initial carrier temperatures vary by many multiples of the
lattice temperature across hundreds of nanometers, a factor that cannot
be accounted for by excess photon energy above the bandgap alone or
in variations of the initial carrier density. Electron microscopy
suggests that morphology plays a critical role in determining the
initial carrier temperature and that carriers in small crystal domains
decay slower than those in large crystal domains. Our results demonstrate
that local disorder dominates the observed carrier behavior, highlighting
the importance of making local rather than averaged measurements in
these materials
Ultrafast Imaging of Carrier Cooling in Metal Halide Perovskite Thin Films
Understanding carrier
relaxation in lead halide perovskites at
the nanoscale is critical for advancing their device physics. Here,
we directly image carrier cooling in polycrystalline CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> films with nanometer spatial resolution.
We observe that upon photon absorption, highly energetic carriers
rapidly thermalize with the lattice at different rates across the
film. The initial carrier temperatures vary by many multiples of the
lattice temperature across hundreds of nanometers, a factor that cannot
be accounted for by excess photon energy above the bandgap alone or
in variations of the initial carrier density. Electron microscopy
suggests that morphology plays a critical role in determining the
initial carrier temperature and that carriers in small crystal domains
decay slower than those in large crystal domains. Our results demonstrate
that local disorder dominates the observed carrier behavior, highlighting
the importance of making local rather than averaged measurements in
these materials
Ultrafast Imaging of Carrier Cooling in Metal Halide Perovskite Thin Films
Understanding carrier
relaxation in lead halide perovskites at
the nanoscale is critical for advancing their device physics. Here,
we directly image carrier cooling in polycrystalline CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> films with nanometer spatial resolution.
We observe that upon photon absorption, highly energetic carriers
rapidly thermalize with the lattice at different rates across the
film. The initial carrier temperatures vary by many multiples of the
lattice temperature across hundreds of nanometers, a factor that cannot
be accounted for by excess photon energy above the bandgap alone or
in variations of the initial carrier density. Electron microscopy
suggests that morphology plays a critical role in determining the
initial carrier temperature and that carriers in small crystal domains
decay slower than those in large crystal domains. Our results demonstrate
that local disorder dominates the observed carrier behavior, highlighting
the importance of making local rather than averaged measurements in
these materials