Simulation Study of an LWFA-based Electron Injector for AWAKE Run 2

The AWAKE experiment aims to demonstrate preservation of injected electron beam quality during acceleration in proton-driven plasma waves. The short bunch duration required to correctly load the wakefield is challenging to meet with the current electron injector system, given the space available to the beamline. An LWFA readily provides short-duration electron beams with sufficient charge from a compact design, and provides a scalable option for future electron acceleration experiments at AWAKE. Simulations of a shock-front injected LWFA demonstrate a 43 TW laser system would be sufficient to produce the required charge over a range of energies beyond 100 MeV. LWFA beams typically have high peak current and large divergence on exiting their native plasmas, and optimisation of bunch parameters before injection into the proton-driven wakefields is required. Compact beam transport solutions are discussed.Comment: Paper submitted to NIMA proceedings for the 3rd European Advanced Accelerator Concepts Workshop. 4 pages, 3 figures, 1 table Changes after revision: Figure 2: figures 2 and 3 of the previous version collated with plots of longitudinal electric field Line 45: E_0 = 96 GV/m Lines 147- 159: evaluation of beam loading made more accurate Lines 107 - 124: discussion of simulation geometry move

Nanophotonics and Nanochemistry: Controlling the Excitation Dynamics for Frequency Up- and Down-Conversion in Lanthanide-Doped Nanoparticles

Nanophotonics is an emerging science dealing with the interaction of light and matter on a nanometer scale and holds promise to produce new generation nanophosphors with highly efficient frequency conversion of infrared (IR) light. Scientists can control the excitation dynamics by using nanochemistry to produce hierarchically built nanostructures and tailor their interfaces. These nanophosphors can either perform frequency up-conversion from IR to visible or ultraviolet (UV) or down-conversion, which results in the IR light being further red shifted. Nanophotonics and nanochemistry open up numerous opportunities for these photon converters, including in high contrast bioimaging, photodynamic therapy, drug release and gene delivery, nanothermometry, and solar cells. Applications of these nanophosphors in these directions derive from three main stimuli. Light excitation and emission within the near-infrared (NIR) “optical transparency window” of tissues is ideal for high contrast <i>in vitro</i> and <i>in vivo</i> imaging. This is due to low natural florescence, reduced scattering background, and deep penetration in tissues. Secondly, the naked eye is highly sensitive in the visible range, but it has no response to IR light. Therefore, many scientists have interest in the frequency up-conversion of IR wavelengths for security and display applications. Lastly, frequency up-conversion can convert IR photons to higher energy photons, which can then readily be absorbed by solar materials. Current solar devices do not use abundant IR light that comprises almost half of solar energy.In this Account, we present our recent work on nanophotonic control of frequency up- and down-conversion in fluoride nanophosphors, and their biophotonic and nanophotonic applications. Through nanoscopic control of phonon dynamics, electronic energy transfer, local crystal field, and surface-induced non-radiative processes, we were able to produce new generation nanophosphors with highly efficient frequency conversion of IR light. We show that nanochemistry plays a vital role in the design and interface engineering of nanophosphors, providing pathways to expand their range of applications. High contrast <i>in vitro</i> and <i>in vivo</i> NIR-to-NIR up- and down-conversion bioimaging were successfully demonstrated by our group, evoking wide interests along this line. We introduced trivalent gadolinium ions into the lattice of the nanophosphors or into the shell layer of nanophosphors in a core/shell configuration to produce novel nanophosphors for multimodal (MRI and optical) imaging. We also demonstrate the security and display applications using photopatternable NIR-to-NIR and NIR-to-visible frequency up-conversion nanophosphors with appropriately engineered surface chemistry. In addition, we present preliminary results on dye-sensitized solar cells using up-conversion in fluoride lattice-based nanophosphors for IR photon harvesting

Changes in Biomolecular Profile in a Single Nucleolus during Cell Fixation

Fixation of biological sample is an essential technique applied in order to “freeze” in time the intracellular molecular content. However, fixation induces changes of the cellular molecular structure, which mask physiological distribution of biomolecules and bias interpretation of results. Accurate, sensitive, and comprehensive characterization of changes in biomolecular composition, occurring during fixation, is crucial for proper analysis of experimental data. Here we apply biomolecular component analysis for Raman spectra measured in the same nucleoli of HeLa cells before and after fixation by either formaldehyde solution or by chilled ethanol. It is found that fixation in formaldehyde does not strongly affect the Raman spectra of nucleolar biomolecular components, but may significantly decrease the nucleolar RNA concentration. At the same time, ethanol fixation leads to a proportional increase (up to 40%) in concentrations of nucleolar proteins and RNA, most likely due to cell shrinkage occurring in the presence of coagulant fixative. Ethanol fixation also triggers changes in composition of nucleolar proteome, as indicated by an overall reduction of the α-helical structure of proteins and increase in the concentration of proteins containing the β-sheet conformation. We conclude that cross-linking fixation is a more appropriate protocol for mapping of proteins in situ. At the same time, ethanol fixation is preferential for studies of RNA-containing macromolecules. We supplemented our quantitative Raman spectroscopic measurements with mapping of the protein and lipid macromolecular groups in live and fixed cells using coherent anti-Stokes Raman scattering nonlinear optical imaging

Ultrafast Dynamics in Multibranched Structures with Enhanced Two-Photon Absorption

The understanding of the mechanism of the enhanced two-photon absorption (TPA) in multibranched chromophore systems is of importance to the design of materials with the large TPA cross-sections and for future applications. In this communication, the mechanism of enhanced TPA properties is investigated. For a dendritic model system, the excited-state dynamics for both population (T1-process) and phase relaxation (T2-process) processes involved are investigated by a combination of time-resolved spectroscopic techniques. The results of time-resolved fluorescence anisotropy are compared with previous results obtained from other branched chromophore systems. It is found that the PRL-701 trimer system, which possesses the large enhancement of two-photon absorption cross-section, gives a faster anisotropy decay (fluorescence upconversion and transient absorption), a longer population relaxation time (fluorescence lifetime), and a weaker coupling to the solvent (a larger photon echo peak shift initial value). New strategies for rational design of large TPA materials can be achieved based on a better understanding of the mechanism of the enhancement

Synthesis of Monodisperse Au, Ag, and Au–Ag Alloy Nanoparticles with Tunable Size and Surface Plasmon Resonance Frequency

Synthesis of Monodisperse Au, Ag, and Au–Ag Alloy Nanoparticles with Tunable Size and Surface Plasmon Resonance Frequenc

Media 1: Realignment-enhanced coherent anti-Stokes Raman scattering and three-dimensional imaging in anisotropic fluids

Originally published in Optics Express on 07 July 2008 (oe-16-14-10617

Experimental and Quantum Chemical Studies of Cooperative Enhancement of Three-Photon Absorption, Optical Limiting, and Stabilization Behaviors in Multibranched and Dendritic Structures

This paper reports on cooperative enhancement of three-photon absorption (3PA) cross section, studied by nonlinear transmission method, in going from a one-branched to a three-branched and then to a dendritic structure. Experimentally, we observe a 72% enhanced 3PA cross-section value in going from the one-branched chromophore to the dendritic chromophore, and a 49% enhanced 3PA cross-section value in going from the one-branched chromophore to the three-branched chromophore, when the 3PA cross-section values are normalized per structure unit. Quantum chemical calculation for the one- and three-branched structures, using the cubic response (CR) theory applied to a single determinant self-consistent field (SCF) reference state, also predicts such an enhancement. Two-dimensional π-delocalization, resulting in extended charge-transfer network in the case of the multibranched structures, is the main cause of the cooperative enhancement. Owing to the increased 3PA cross-section value for the dendritic chromophore, improved optical limiting performance at an optical communication wavelength of 1310 nm was observed, compared with the one-branched (or three-branched) chromophore, using comparable structure-unit-based concentrations. Optical stabilization capability of the dendritic chromophore was also observed at this wavelength

Mitochondrial Dysfunction: A Prelude to Neuropathogenesis of SARS-CoV‑2

The SARS-CoV-2 virus is notorious for its neuroinvasive capability, causing multiple neurological conditions. The neuropathology of SARS-CoV-2 is increasingly attributed to mitochondrial dysfunction of brain microglia cells. However, the changes in biochemical content of mitochondria that drive the progression of neuro-COVID remain poorly understood. Here we introduce a Raman microspectrometry approach that enables the molecular profiling of single cellular organelles to characterize the mitochondrial molecular makeup in the infected microglia cells. We found that microglia treated with either spike protein or heat-inactivated SARS-CoV-2 trigger a dramatic reduction in mtDNA content and an increase in phospholipid saturation levels. At the same time, no significant changes were detected in Golgi apparatus and in lipid droplets, the organelles that accommodate biogenesis and storage of lipids. We hypothesize that transformations in mitochondria are caused by increased synthesis of reactive oxygen species in these organelles. Our findings call for the development of mitochondria-targeted therapeutic approaches to limit neuropathology associated with SARS-CoV-2

Media 2: Realignment-enhanced coherent anti-Stokes Raman scattering and three-dimensional imaging in anisotropic fluids

Originally published in Optics Express on 07 July 2008 (oe-16-14-10617

Lifetime of the ³H₄ Electronic State in Tm³⁺-Doped Upconverting Nanoparticles for NIR Nanothermometry

Emission bands from thermally coupled states in lanthanide-doped nanoparticles have been studied for ratiometric nanothermometry in biological applications. Unfortunately certain factors such as water absorption distort the intensity, limiting the accuracy of ratiometric nanothermometry. However, the decay time of such states does not suffer from such distortions. We introduce the decay time of the 3H4 state in Yb3+, Tm3+-doped nanoparticles for improved nanothermometry. The strong 800 nm upconversion emission exists in the first biological transparency window. This is the first use of a single upconversion band for lifetime nanothermometry