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A pump-probe scheme with a single chirped pulse to image electron and nuclear dynamics in molecules
摘要： A single chirped few-femtosecond pulse can be used to control and image coupled electron-nuclear dynamics. Using full ab initio simulations of the simplest molecule, H+2, as a prototype target, we show that for intermediate values of the chirp, interference between sequential and direct contributions enables significant control over ionization yields, even when taking into account the effective decoherence introduced by nuclear motion and the presence of an electronic continuum. For larger values of the chirp, the single chirped pulse reproduces a classical pump-probe setup, with the chirp parameter mapping an effective time delay between the pumping and probing frequencies of the pulse. After demonstrating this numerically, we present a full analytical solution for the two-photon ionization amplitudes that provides an intuitive analogy between the molecular dynamics induced by a single chirped pulse and a traditional pump-probe setup.
关键词： pump-probe scheme,attosecond science,chirped pulse,molecular ionization,electron-nuclear dynamics
更新于2025-09-23 15:21:01
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Development of a Selective Fluorescent Probe for Hypochlorous Acid Detection and Imaging
摘要： The reactive oxygen species (ROS), hypochlorous acid (HOCl), participates in many important biological events. For example, this ROS is the main active agent to kill invading microbes by immune system. HOCl is produced by H2O2 and Cl? in a myeloperoxidase (MPO) catalyzed process that occurs in response to inflammatory stimuli. Because HOCl reacts with important biological molecules and it causes cell damage, its uncontrolled production is involved in some human maladies such as arthritis. Detection and imaging HOCl in vivo are critical components of studies aimed at elucidating the biological functions of this ROS. Owing to several advantageous features including high selectivities and sensitivities, short response times and simple preparation methods, molecular fluorescent probes have become powerful tools for detecting biologically important substances and bio-imaging. It is essential to develop highly selective and sensitive fluorescent probes for HOCl for bio-applications. In the study described below, we demonstrated that spiro[isobenzofuran-30,60-dihydroxy-1(3H),90-[9H]thioxanthen]-3-one (TF) is an ideal fluorescent probe for HOCl because it undergoes a fluorescence enhancement upon being selectively chlorinated by this ROS.
关键词： Cell imaging,Fluorescent probe,Hypochlorous acid detection
更新于2025-09-23 15:21:01
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[Laser Institute of America ICALEO? 2015: 34th International Congress on Laser Materials Processing, Laser Microprocessing and Nanomanufacturing - Atlanta, Georgia, USA (October 18–22, 2015)] International Congress on Applications of Lasers & Electro-Optics - Microstructural effects induced by laser shock peening for mitigation of stress corrosion cracking
摘要： Stress corrosion cracking is a phenomenon that can lead to rapid, sudden failure of metallic products. In this paper we examine the mechanisms of SCC mitigation of stainless steel and brass samples using laser shock peening (LSP). The behavior of hydrogen within the crystal lattice is one of the most dominant contributors to SCC, where uptake of hydrogen strains the lattice and increases its hardness. Cathodic charging of the metallic samples in 1M sulfuric acid was performed in order to accelerate hydrogen uptake. Non-treated samples underwent hardness increases of 28%, but LSP treated samples only increased in the range of 0 to 8%, indicative that LSP keeps hydrogen from permeating into the metal. Mechanical U-bends subjected and MgCl2 environments are analyzed, to determine changes in fracture morphology. Surface chemical effects are addressed via Kelvin Probe Force Microscopy, which is used for finding changes in the work function caused by LSP treatment. A finite element model of material deformation from U-bending was developed to analyze and compare the induced stresses. With LSP, there is a potential for overprocessing the samples, whereby negative effects refinement, to corrosion martensite formation) can arise. Detection of any martensite phases formed is performed using x-ray diffraction. We find LSP to be beneficial for stainless steel but does not improve brass’s SCC resistance. With our analysis methods we provide a further understanding of the process whereby LSP reduces subsequently highlight SCC for important implementation of the process.
关键词： Brass,Stainless steel,Hydrogen uptake,Stress corrosion cracking,Cathodic charging,Kelvin Probe Force Microscopy,Laser shock peening,Finite element model
更新于2025-09-23 15:21:01
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Fast response fluorogenic probe for visualizing hypochlorite in living cells and Zebrafishes
摘要： A novel fast response and visible fluorogenic probe (D1) for monitoring hypochlorite (ClO?) has been developed based on specific ClO? removal of a C=N bond. The response of the probe to ClO? showed increases linearly, and the fluorescence intensity heighten about 25 times. D1 responses to ClO? were observed with high selectivity and sensitivity within 10 s by naked eyes. D1 can not only detect the level of hypochlorite in vitro such as urine, but also monitoring hypochlorite content in extremely cold condition as low as -78oC. Meanwhile, the good biocompatibility guaranteed the use of D1 to detect intracellular ClO? under confocal microscopy. Moreover, D1 has been successfully applied to monitor the exogenous and endogenous ClO? in Zebrafishes with fluorescence imaging.
关键词： Zebrafishes,live cell imaging,hypochlorite,fast response,fluorogenic probe
更新于2025-09-23 15:21:01
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A coumarin-based dual optical probe for homocysteine with rapid response time, high sensitivity and selectivity
摘要： In this study, a new coumarin-based fluorescent and chromogenic dual channel probe (DC) was used for the selective detection of homocysteine (Hcy) over other amino acids, especially for cysteine (Cys) and glutathione (GSH). When Hcy is present in the solution, the remarkable fluorescence enhancement and obvious blue shift in UV–vis spectra can be observed. In addition, the color change from purple to yellow can be observed clearly by unaided eyes. This probe DC has fast response time, excellent sensitivity and selectivity to Hcy. A linear relationship exists between the ratio of emissions at 486 and 625 nm, and Hcy can be detected in a wide concentration range (0 to 200 μM). The signal-to-background ratio of fluorescence at 486 nm can reach 8.4, and the detection limit is calculated to be 3.5 μM. The response mechanism is proved to be the Michael addition reaction by Hcy. Preliminary results on cell imaging enable the practical application of Hcy tracing in living cells.
关键词： Sensor,Fluorescent probe,dual optical probe,Coumarin,Homocysteine,Cell imaging
更新于2025-09-23 15:19:57
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Application of Atom Probe Tomography to Complex Microstructures of Laser Additively Manufactured Samples
摘要： Additive Manufacturing (AM) technologies have gained increasing interest across multiple industrial sectors ranging from biomedical to aerospace. AM is not only used for prototyping, but also for tooling as well as for final part production. The computer-controlled, layer-by-layer building up process allows for increased design freedom enabling to produce almost any shape. Additional benefits are potential resource efficiency, increased product customization and lightweight design. Two prominent metal-based laser AM (LAM) techniques are laser powder bed fusion (LPBF) and laser metal deposition (LMD). In LPBF, a focused laser beam is scanned over a bed filled with metal powder to locally melt and fuse the powder to produce fully dense metal parts. The next layer of powder is then distributed and the laser scans again. LMD is a nozzle-based AM process in which a focused laser beam creates a melt pool in the build’s surface. Metallic powder is then injected into the melt pool through a nozzle. The 3D part is built by moving the nozzle/laser assembly forward track by track and layer by layer. Material produced by LAM exhibits a unique thermal history: initially, the material is cooled rapidly from the liquid state in the meltpool. Subsequently, the material experiences a cyclic reheating, the so-called intrinsic heat treatment (IHT), as neighboring tracks and further layers are deposited during the LAM process. Consequences of this thermal history are very complex, sometimes hierarchical microstructures with inhomogeneities at scales ranging from nanometers up millimeters. Fully understanding and characterizing these microstructures is challenging and requires the combination of methods spanning a similar range: from light optical microscopy (LOM) to electron microscopy to atom probe tomography (APT). Here we present examples how APT can deliver valuable information on complex microstructures to better understand the IHT, rapid solidification as well as phase separation in different metallic alloys. Here I will discuss examples in steel, Al- and Ni-based superalloys, and high entropy alloys (HEA).
关键词： Laser Additive Manufacturing,Additive Manufacturing,Phase Separation,Microstructures,Atom Probe Tomography,Rapid Solidification,Intrinsic Heat Treatment
更新于2025-09-23 15:19:57
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Many-particle excitations in non-covalently doped single-walled carbon nanotubes
摘要： Doping of single-walled carbon nanotubes leads to the formation of new energy levels which are able to participate in optical processes. Here, we investigate (6,5)-single walled carbon nanotubes doped in a solution of hydrochloric acid using optical absorption, photoluminescence, and pump-probe transient absorption techniques. We find that, beyond a certain level of doping, the optical spectra of such nanotubes exhibit the spectral features related to two doping-induced levels, which we assign to a localized exciton X and a trion T, appearing in addition to an ordinary exciton E1. We evaluate the formation and relaxation kinetics of respective states and demonstrate that the kinetics difference between E1 and X energy levels perfectly matches the kinetics of the state T. This original finding evidences the formation of trions through nonradiative relaxation via the X level, rather than via a direct optical excitation from the ground energy state of nanotubes.
关键词： exciton,doping,optical absorption,pump-probe transient absorption,photoluminescence,trion,single-walled carbon nanotubes
更新于2025-09-23 15:19:57
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Glymphatic clearance of simulated silicon dispersion in mouse brain analyzed by laser induced breakdown spectroscopy
摘要： Silicon-based devices, such as neural probes, are increasingly used as electrodes for receiving electrical signals from neural tissue. Neural probes used chronically have been known to induce inflammation and elicit an immune response. The current study detects and evaluates silicon dispersion from a concentrated source in the mouse brain using laser induced breakdown spectroscopy. Element lines for Si (I) were found at the injection site at approximately 288 nm at 3hr post-implantation, even with tissue perfusion, indicating possible infusion into neural tissue. At 24hr and 1-week post-implantation, no silicon lines were found, indicating clearance. An isolated immune response was found by CD68 macrophage response at 24hr post injection. Future studies should measure chronic silicon exposure to determine if the inflammatory response is proportional to silicon administration. The present type of protocol, coupling laser induced breakdown spectroscopy, neuroimaging, histology, immunohistochemistry, and determination of clearance could be used to investigate the glymphatic system and different tissue states such as in disease (e.g. Alzheimer's).
关键词： Inflammation,Silicon,Neuroscience,Biophysics,Physics methods,Probe,Toxicology,Physics,Optics,Immune response,Electrode
更新于2025-09-23 15:19:57
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Investigation of optical fiber-tip probes for common and ultrafast SERS
摘要： In this study, we performed a three-dimensional computational experiment on ultrashort pulse propagation in an optical fiber-tip probe that is decorated with gold nanoparticles (NPs) using a constant structure for the probe’s dielectric taper and different spatial configurations of the gold nanoparticles. Interestingly, a hot spot with the highest amplitude of the electric field was found not along the same chain of the NPs but between terminal NPs of neighboring chains of NPs at the probe’s tip (the amplitude of the electric field in the hot spots between the NPs along the same chain was of the order of 101, while that between terminal NPs of neighboring chains was of the order of 103). We eventually identified a configuration with only six terminal nanoparticles (Config4) which is characterized by the highest electric field amplitude enhancement and can provide the highest spatial resolution in the SERS interrogation of an object of interest. The ultrashort temporal responses of the hot spots for all configurations exhibited relatively high pulse elongation (relative elongation was greater than 4.3%). At the same time, due to the reflection of the incident pulse and consequent interference, the temporal responses of most hot spots contained several peaks for all configurations except for the optimum Config4. Nonetheless, the ultrashort temporal responses of all hot spots for Config4 were characterized by a single peak but with a relatively large pulse elongation (relative elongation was 234.1%). The results indicate that further examination of this new structure of a nanoparticles-coated optical fiber-tip probe with only six terminal NPs may provide attractive characteristics for its practical applications.
关键词： gold nanoparticles,femtosecond pulse,optical fiber-tip probe,ultrafast nanophotonics.,surface-enhanced Raman spectroscopy,temporal response
更新于2025-09-23 15:19:57
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Ultrafast dynamics observation during femtosecond laser-material interaction
摘要： Femtosecond laser technology has attracted significant attention from the viewpoints of fundamental and application; especially femtosecond laser processing materials present the unique mechanism of laser-material interaction. Under the extreme nonequilibrium conditions imposed by femtosecond laser irradiation, many fundamental questions concerning the physical origin of the material removal process remain unanswered. In this review, cutting-edge ultrafast dynamic observation techniques for investigating the fundamental questions, including time-resolved pump-probe shadowgraphy, ultrafast continuous optical imaging, and four-dimensional ultrafast scanning electron microscopy, are comprehensively surveyed. Each technique is described in depth, beginning with its basic principle, followed by a description of its representative applications in laser-material interaction and its strengths and limitations. The consideration of temporal and spatial resolutions and panoramic measurement at different scales are two major challenges. Hence, the prospects for technical advancement in this field are discussed finally.
关键词： ultrafast dynamics,ultrafast continuous optical imaging,femtosecond laser manufacturing,4D ultrafast scanning electron microscopy,pump-probe shadowgraphy
更新于2025-09-23 15:19:57