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Ultrafast pump-probe microscopy reveals spatial heterogeneity in material properties including charge and energy transfer, electron-phonon coupling, and vibrational dynamics. At high spatial resolution, weak nonlinear signals often require point scanning with significant signal averaging, limiting studies of non-repeatable processes or systems prone to photodamage from prolonged laser exposure. To overcome these limitations, we introduce a wide-field pump–probe approach that integrates Parallel Rapid Imaging with Spectroscopic Mapping (PRISM) and a self-referencing method, suppressing noise by more than two orders of magnitude. Our technique exploits spatial correlations within the field of view to denoise and suppress laser intensity fluctuations without a reference detector, enabling acquisition of over one million pump–probe traces in under a second. This capability supports high-throughput material screening, real-time ultrafast spectroscopy, and investigations of non-reversible dynamics. Applied to few-layer WSe₂ and monolayer WSe₂/MoSe₂ heterostructures, the method resolves vibrational modes and substrate-induced coupling previously hidden by laser noise. A wide-field pump–probe microscopy method captures over a million ultrafast traces per second with reduced noise and no reference detector, revealing hidden vibrational modes and couplings in 2D materials and heterostructure.

Light-harvesting antenna complexes transfer energy from sunlight to photosynthetic reaction centers where charge separation drives cellular metabolism. The process through which pigments transfer excitation energy involves a complex choreography of coherent and incoherent processes mediated by the surrounding protein and solvent environment. The recent discovery of coherent dynamics in photosynthetic light-harvesting antennae has motivated many theoretical models exploring effects of interference in energy transfer phenomena. In this work, we provide experimental evidence of long-lived quantum coherence between the spectrally separated B800 and B850 rings of the light-harvesting complex 2 (LH2) of purple bacteria. Spectrally resolved maps of the detuning, dephasing, and the amplitude of electronic coupling between excitons reveal that different relaxation pathways act in concert for optimal transfer efficiency. Furthermore, maps of the phase of the signal suggest that quantum mechanical interference between different energy transfer pathways may be important even at ambient temperature. Such interference at a product state has already been shown to enhance the quantum efficiency of transfer in theoretical models of closed loop systems such as LH2.

Photosynthetic antenna complexes capture and concentrate solar radiation by transferring the excitation to the reaction center that stores energy from the photon in chemical bonds. This process occurs with near-perfect quantum efficiency. Recent experiments at cryogenic temperatures have revealed that coherent energy transfer—a wave-like transfer mechanism—occurs in many photosynthetic pigment-protein complexes. Using the Fenna–Matthews–Olson antenna complex (FMO) as a model system, theoretical studies incorporating both incoherent and coherent transfer as well as thermal dephasing predict that environmentally assisted quantum transfer efficiency peaks near physiological temperature; these studies also show that this mechanism simultaneously improves the robustness of the energy transfer process. This theory requires long-lived quantum coherence at room temperature, which never has been observed in FMO. Here we present evidence that quantum coherence survives in FMO at physiological temperature for at least 300 fs, long enough to impact biological energy transport. These data prove that the wave-like energy transfer process discovered at 77 K is directly relevant to biological function. Microscopically, we attribute this long coherence lifetime to correlated motions within the protein matrix encapsulating the chromophores, and we find that the degree of protection afforded by the protein appears constant between 77 K and 277 K. The protein shapes the energy landscape and mediates an efficient energy transfer despite thermal fluctuations.

Electronic and vibrational correlations report on the dynamics and structure of molecular species, yet revealing these correlations experimentally has proved extremely challenging. Here, we demonstrate a method that probes correlations between states within the vibrational and electronic manifold with quantum coherence selectivity. Specifically, we measure a fully coherent four-dimensional spectrum which simultaneously encodes vibrational–vibrational, electronic–vibrational and electronic–electronic interactions. By combining near-impulsive resonant and non-resonant excitation, the desired fifth-order signal of a complex organic molecule in solution is measured free of unwanted lower-order contamination. A critical feature of this method is electronic and vibrational frequency resolution, enabling isolation and assignment of individual quantum coherence pathways. The vibronic structure of the system is then revealed within an otherwise broad and featureless 2D electronic spectrum. This method is suited for studying elusive quantum effects in which electronic transitions strongly couple to phonons and vibrations, such as energy transfer in photosynthetic pigment–protein complexes. Electronic and vibrational correlations report on the dynamics and structure of molecular species, yet revealing these correlations experimentally is challenging. Here the authors develop a method called GAMERS that probes correlations between states within the vibrational and electronic manifold with quantum coherence selectivity.

Electronic structure and dynamics determine material properties and behavior. Important time scales for electronic dynamics range from attoseconds to milliseconds. Two-dimensional optical spectroscopy has proven an incisive tool to probe fast spatiotemporal electronic dynamics in complex multichromophoric systems. However, acquiring these spectra requires long point-by-point acquisitions that preclude observations on the millisecond and microsecond time scales. Here we demonstrate that imaging temporally encoded information within a homogeneous sample allows mapping of the evolution of the electronic Hamiltonian with femtosecond temporal resolution in a single-laser-shot, providing real-time maps of electronic coupling. This method, which we call GRadient-Assisted Photon Echo spectroscopy (GRAPE), eliminates phase errors deleterious to Fourier spectroscopies while reducing the acquisition time by orders of magnitude using only conventional optical components. In analogy to MRI in which magnetic field gradients are used to create spatial correlation maps, GRAPE spectroscopy takes advantage of a similar type of spatial encoding to construct electronic correlation maps. Unlike magnetic resonance, however, this spatial encoding of the nonlinear polarization along the excitation frequency axis of the two-dimensional spectrum results in no loss in signal while simultaneously reducing overall noise. Correlating the energy transfer events and electronic coupling occurring in tens of femtoseconds with slow dynamics on the subsecond time scale is fundamentally important in photobiology, solar energy research, nonlinear spectroscopy, and optoelectronic device characterization.

Compressive sensing allows signals to be efficiently captured by exploiting their inherent sparsity. Here we implement sparse sampling to capture the electronic structure and ultrafast dynamics of molecular systems using phase-resolved 2D coherent spectroscopy. Until now, 2D spectroscopy has been hampered by its reliance on array detectors that operate in limited spectral regions. Combining spatial encoding of the nonlinear optical response and rapid signal modulation allows retrieval of state-resolved correlation maps in a photosynthetic protein and carbocyanine dye. We report complete Hadamard reconstruction of the signals and compression factors as high as 10, in good agreement with array-detected spectra. Single-point array reconstruction by spatial encoding (SPARSE) Spectroscopy reduces acquisition times by about an order of magnitude, with further speed improvements enabled by fast scanning of a digital micromirror device. We envision unprecedented applications for coherent spectroscopy using frequency combs and super-continua in diverse spectral regions. Many spectral regions lack the sensitive pixel array detectors needed for multidimensional spectroscopy. Here, the authors report a method for rapidly collecting multidimensional optical spectra without an array detector, instead utilizing spatial encoding and a single-element detector.

Achieving control of light-material interactions for photonic device applications at nanoscale dimensions will require structures that guide electromagnetic energy with a lateral mode confinement below the diffraction limit of light. This cannot be achieved by using conventional waveguides 1 or photonic crystals 2 . It has been suggested that electromagnetic energy can be guided below the diffraction limit along chains of closely spaced metal nanoparticles 3 , 4 that convert the optical mode into non-radiating surface plasmons 5 . A variety of methods such as electron beam lithography 6 and self-assembly 7 have been used to construct metal nanoparticle plasmon waveguides. However, all investigations of the optical properties of these waveguides have so far been confined to collective excitations 8 , 9 , 10 , and direct experimental evidence for energy transport along plasmon waveguides has proved elusive. Here we present observations of electromagnetic energy transport from a localized subwavelength source to a localized detector over distances of about 0.5 μm in plasmon waveguides consisting of closely spaced silver rods. The waveguides are excited by the tip of a near-field scanning optical microscope, and energy transport is probed by using fluorescent nanospheres.

Magnetic resonance imaging (MRI) can elucidate the interior structure of an optically opaque object in unparalleled detail but is ultimately limited by the need to enclose the object within a detection coil; acquiring the image with increasingly smaller pixels reduces the sensitivity, because each pixel occupies a proportionately smaller fraction of the detector's volume. We developed a technique that overcomes this limitation by means of remotely detected MRI. Images of fluids flowing in channel assemblies are encoded into the phase and intensity of the constituent molecules' nuclear magnetic resonance signals and then decoded by a volume-matched detector after the fluids flow out of the sample. In combination with compressive sampling, we thus obtain microscopic images of flow and velocity distributions ~10⁶ times faster than is possible with conventional MRI on this hardware. Our results illustrate the facile integration of MRI with microfluidic assays and suggest generalizations to other systems involving microscopic flow.

Pore structure and connectivity determine how microstructured materials perform in applications such as catalysis, fluid storage and transport, filtering or as reactors. We report a model study on silica aerogel using a time-of-flight magnetic resonance imaging technique to characterize the flow field and explain the effects of heterogeneities in the pore structure on gas flow and dispersion with 129 Xe as the gas-phase sensor. The observed chemical shift allows the separate visualization of unrestricted xenon and xenon confined in the pores of the aerogel. The asymmetrical nature of the dispersion pattern alludes to the existence of a stationary and a flow regime in the aerogel. An exchange time constant is determined to characterize the gas transfer between them. As a general methodology, this technique provides insights into the dynamics of flow in porous media where several phases or chemical species may be present.

The phenomenon of magnetic resonance has played a critical role in our current understanding of the physical world. From routine organic product analysis to complex protein structure determination to materials chemistry and medical imaging, magnetic resonance has provided the chemist, biologist, physicist, and medical practitioner with an incredibly powerful tool to explore the world around us. With the advent of time-domain nuclear magnetic resonance (NMR) and its imaging counterpart, magnetic resonance imaging (MRI), systems undergoing dynamics can be studied in a broad range of spatial and temporal regimes. However, the limitation in sensitivity owing to the weak nuclear magnetic moment generally precludes examination of systems on the micron scale with high spatial and temporal resolution. The work presented in this dissertation aims to challenge the traditional paradigm of high field magnetic resonance as being only applicable to relatively large systems undergoing slow dynamics. While a variety of topics are covered, each shares in common the ability to take advantage of the time domain in non-trivial ways. The main focus is on using multidimensional encoding and detection schemes that act to increase the sensitivity while providing for additional dynamical information about the system under study. Experimental results on systems ranging from porous materials to lab-on-a-chip devices are presented that validate the approach.