134 research outputs found
Seeing the vibrational breathing of a single molecule through time-resolved coherent anti-Stokes Raman scattering
The motion of chemical bonds within molecules can be observed in real time,
in the form of vibrational wavepackets prepared and interrogated through
ultrafast nonlinear spectroscopy. Such nonlinear optical measurements are
commonly performed on large ensembles of molecules, and as such, are limited to
the extent that ensemble coherence can be maintained. Here, we describe
vibrational wavepacket motion on single molecules, recorded through
time-resolved, surface-enhanced, coherent anti-Stokes Raman scattering. The
required sensitivity to detect the motion of a single molecule, under ambient
conditions, is achieved by equipping the molecule with a dipolar nano-antenna
(a gold dumbbell). In contrast with measurements in ensembles, the vibrational
coherence on a single molecule does not dephase. It develops phase fluctuations
with characteristic statistics. We present the time evolution of discretely
sampled statistical states, and highlight the unique information content in the
characteristic, early-time probability distribution function of the signal.Comment: 17 pages, 5 figure
Infrared chemical imaging through nondegenerate two-photon absorption in silicon-based cameras
Chemical imaging based on mid-infrared (MIR) spectroscopic contrast is an
important technique with a myriad of applications, including biomedical imaging
and environmental monitoring. Current MIR cameras, however, lack in performance
and are much less affordable compared to mature Si-based devices, which operate
in the visible and near-infrared. Here we demonstrate fast MIR chemical imaging
through non-degenerate two-photon absorption (NTA) in a standard Si-based
charge-coupled device (CCD). We show that wide-field MIR images can be obtained
at 100 ms exposure times using picosecond pulse energies of only a few fJ per
pixel through NTA directly on the CCD chip. Because this on-chip approach does
not rely on phase-matching, it is alignment-free and does not necessitate
complex post-processing of the images. We emphasize the utility of this
technique through chemically selective MIR imaging of polymers and biological
samples, including MIR videos of moving targets, physical processes and live
nematodes
High-speed 2D and 3D mid-IR imaging with an InGaAs camera
Recent work on mid-infrared (MIR) detection through the process of
non-degenerate two-photon absorption (NTA) in semiconducting materials has
shown that wide-field MIR imaging can be achieved with standard Si cameras.
While this approach enables MIR imaging at high pixel densities, the low
nonlinear absorption coefficient of Si prevents fast NTA-based imaging at lower
illumination doses. Here we overcome this limitation by using InGaAs as the
photosensor. Taking advantage of the much higher nonlinear absorption
coefficient of this direct bandgap semiconductor, we demonstrate high-speed MIR
imaging up to 500 fps with under 1 ms exposure per frame, enabling 2D or 3D
mapping without pre- or post-processing of the image.Comment: 7 pages, 5 Figure
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Spaceflight Activates Lipotoxic Pathways in Mouse Liver
Spaceflight affects numerous organ systems in the body, leading to metabolic dysfunction that may have long-term consequences. Microgravity-induced alterations in liver metabolism, particularly with respect to lipids, remain largely unexplored. Here we utilize a novel systems biology approach, combining metabolomics and transcriptomics with advanced Raman microscopy, to investigate altered hepatic lipid metabolism in mice following short duration spaceflight. Mice flown aboard Space Transportation System -135, the last Shuttle mission, lose weight but redistribute lipids, particularly to the liver. Intriguingly, spaceflight mice lose retinol from lipid droplets. Both mRNA and metabolite changes suggest the retinol loss is linked to activation of PPARα-mediated pathways and potentially to hepatic stellate cell activation, both of which may be coincident with increased bile acids and early signs of liver injury. Although the 13-day flight duration is too short for frank fibrosis to develop, the retinol loss plus changes in markers of extracellular matrix remodeling raise the concern that longer duration exposure to the space environment may result in progressive liver damage, increasing the risk for nonalcoholic fatty liver disease
Mapping Molecular Orientation with Phase Sensitive Vibrationally Resonant Sum-Frequency Generation Microscopy
We demonstrate a phase sensitive, vibrationally resonant sum-frequency generation (PSVR-SFG) microscope that combines high resolution, fast image acquisition speed, chemical selectivity, and phase sensitivity. Using the PSVR-SFG microscope, we generate amplitude and phase images of the second-order susceptibility of collagen I fibers in rat tail tendon tissue on resonance with the methylene vibrations of the protein. We find that the phase of the second-order susceptibility shows dependence on the effective polarity of the fibril bundles, revealing fibrous collagen domains of opposite orientations within the tissue. The presence of collagen microdomains in tendon tissue may have implications for the interpretation of the mechanical properties of the tissue. [Image: see text
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