PLD-produced crystalline antireflection coatings and dichroic mirrors

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Ultra-thin Cr : YAG layers for Q-switching

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Femtosecond Pumping Rate Dependence of Fragmentation Mechanisms in Matrix-Assisted Laser Desorption Ionization

The fragmentation mechanisms of matrix-assisted laser desorption/ionization (MALDI) for femtosecond ultraviolet laser pulses in a transmission geometry are characterized on the basis of the well-known benzyltriphenylphosphonium (BTP) thermometer ion. We demonstrate that the survival yield of BTP approaches unity under these conditions, which suggests that a minimal amount of fragmentation is occurring. It is shown that, while the survival yield of BTP is insensitive to the fluence within the studied fluence range, the magnitude of fragmentation for the matrix increased notably with increasing fluence. While nonlinear absorption and ionization are expected to lead to large matrix fragmentation rates, the high BTP survival yields indicate a reduced amount of energy being transferred from the matrix to these BTP thermometer ions. The femtosecond ablation employed here results in increased heating rates and occurs within the fully stress-confinement regime, which minimizes the matrix-analyte interaction during the ablation event. This interpretation is supported by our finding that angiotensin was the largest biomolecule which could be routinely be measured with femtosecond pulses. The spatio-temporal overlap between a neutral biomolecule and matrix ions resulting from this process is too short to result in sufficient proton exchange for ionization.<br /

Femtosecond Pumping Rate Dependence of Fragmentation Mechanisms in Matrix-Assisted Laser Desorption Ionization

The fragmentation mechanisms of matrix-assisted laser desorption/ionization (MALDI) for femtosecond ultraviolet laser pulses in a transmission geometry are characterized on the basis of the well-known benzyltriphenylphosphonium (BTP) thermometer ion. We demonstrate that the survival yield of BTP approaches unity under these conditions, which suggests that a minimal amount of fragmentation is occurring. It is shown that, while the survival yield of BTP is insensitive to the fluence within the studied fluence range, the magnitude of fragmentation for the matrix increased notably with increasing fluence. While nonlinear absorption and ionization are expected to lead to large matrix fragmentation rates, the high BTP survival yields indicate a reduced amount of energy being transferred from the matrix to these BTP thermometer ions. The femtosecond ablation employed here results in increased heating rates and occurs within the fully stress-confinement regime, which minimizes the matrix-analyte interaction during the ablation event. This interpretation is supported by our finding that angiotensin was the largest biomolecule which could be routinely be measured with femtosecond pulses. The spatio-temporal overlap between a neutral biomolecule and matrix ions resulting from this process is too short to result in sufficient proton exchange for ionization.<br

Two-Dimensional Confinement for Generating Thin Single Crystals for Time-Resolved Electron Diffraction and Spectroscopy: An Intramolecular Proton Transfer Study

Thin single organic crystals (≤1 μm) with large area (≥100 × 100 μm2) are desirable to explore their photoinduced processes using transmission-based ultrafast spectroscopy and electron-diffraction techniques. Here we present a method to grow thin large area single crystals of a prototypical proton transfer system, 1,5-dihydroxyanthraquinone. As a proof of concept, we perform optical measurements on as-grown samples and recorded the data in transmission mode

Time-resolved crystallography reveals allosteric communication aligned with molecular breathing

A comprehensive understanding of protein function demands correlating structure and dynamic changes. Using time-resolved serial synchrotron crystallography, we visualized half-of-the-sites reactivity and correlated molecular-breathing motions in the enzyme fluoroacetate dehalogenase. Eighteen time points from 30 milliseconds to 30 seconds cover four turnover cycles of the irreversible reaction. They reveal sequential substrate binding, covalent-intermediate formation, setup of a hydrolytic water molecule, and product release. Small structural changes of the protein mold and variations in the number and placement of water molecules accompany the various chemical steps of catalysis. Triggered by enzyme-ligand interactions, these repetitive changes in the protein framework’s dynamics and entropy constitute crucial components of the catalytic machinery

Torsionally broken symmetry assists infrared excitation of biomimetic charge-coupled nuclear motions in the electronic ground state

International audienceThe concerted interplay between reactive nuclear and electronic motions in molecules actuates chemistry. Here, we demonstrate that out-of-plane torsional deformation and vibrational excitation of stretching motions in the electronic ground state modulate the charge-density distribution in a donor-bridge-acceptor molecule in solution. The vibrationally-induced change, visualised by transient absorption spectroscopy with a mid-infrared pump and a visible probe, is mechanistically resolved by ab initio molecular dynamics simulations. Mapping the potential energy landscape attributes the observed charge-coupled coherent nuclear motions to the population of the initial segment of a double-bond isomerization channel, also seen in biological molecules. Our results illustrate the pivotal role of pre-twisted molecular geometries in enhancing the transfer of vibrational energy to specific molecular modes, prior to thermal redistribution. This motivates the search for synthetic strategies towards achieving potentially new infrared-mediated chemistry

Vibrational Excitation Initiates Biomimetic Charge-Coupled Motions in the Electronic Ground State

The concerted interplay between reactive nuclear and electronic motions in molecules actuates chemistry. Manipulating reaction pathways to achieve product selectivity via precise control of light-molecule interactions has allured chemists for decades. Yet it remains an elusive challenge in the electronic ground state, where conventional thermally-driven chemistry occurs. Here, we demonstrate that ground-state vibrational excitation of localised bridge modes initiates charge transfer in a donor-bridge-acceptor molecule in solution. The vibrationally-induced change in the ground-state electronic configuration is visualised by transient absorption spectroscopy, involving a mid-infrared pump and a visible probe, and detailed ab initio molecular dynamics simulations. Mapping the potential energy landscape unravels a hitherto undocumented charge-transfer-assisted double-bond isomerization channel in the electronic ground state. The reaction pathway bears remarkable parallels with the thermal isomerization process in rhodopsin, the retinal protein responsible for scotopic vision. Our results illustrate a generic protocol for activating key vibrational modes to drive photo-triggered ground-state reactions and motivate synthetic and catalytic strategies to achieving potentially new chemistry. </p

The hit-and-return system enables efficient time-resolved serial synchrotron crystallography

We present a ‘hit-and-return’ (HARE) method for time-resolved serial synchrotron crystallography with time resolution from milliseconds to seconds or longer. Timing delays are set mechanically, using the regular pattern in fixed-target crystallography chips and a translation stage system. Optical pump-probe experiments to capture intermediate structures of fluoroacetate dehalogenase binding to its ligand demonstrated that data can be collected at short (30 ms), medium (752 ms) and long (2,052 ms) intervals