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Photophoretic force measurement on microparticles in binary complex plasmas
摘要： This article presents a method to measure the photophoretic force on microparticles in complex plasmas. A laser heating setup is used to increase the kinetic temperatures of binary mixtures composed of melamine-formaldehyde (MF) and silica (SiO2) particles. The temperature gain of both particle species due to the additional thermal reservoir is compared to a laser force model. Contributions of radiation pressure and photophoretic forces are determined through a variation of neutral gas pressure and application of Lorenz-Mie theory. The photophoretic force is found to be significant for MF particles at typical conditions in complex plasma experiments.
关键词： photophoretic force,microparticles,radiation pressure,complex plasmas,Lorenz-Mie theory,binary mixtures,laser heating
更新于2025-09-23 15:22:29
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Laser-heated capillary discharge plasma waveguides for electron acceleration to 8 GeV
摘要： A plasma channel created by the combination of a capillary discharge and inverse Bremsstrahlung laser heating enabled the generation of electron bunches with energy up to 7.8 GeV in a laser-driven plasma accelerator. The capillary discharge created an initial plasma channel and was used to tune the plasma temperature, which optimized laser heating. Although optimized colder initial plasma temperatures reduced the ionization degree, subsequent ionization from the heater pulse created a fully ionized plasma on-axis. The heater pulse duration was chosen to be longer than the hydrodynamic timescale of ~1 ns, such that later temporal slices were more efficiently guided by the channel created by the front of the pulse. Simulations are presented which show that this thermal self-guiding of the heater pulse enabled channel formation over 20 cm. The post-heated channel had lower on-axis density and increased focusing strength compared to relying on the discharge alone, which allowed for guiding of relativistically intense laser pulses with a peak power of 0.85 PW and wakefield acceleration over 15 diffraction lengths. Electrons were injected into the wake in multiple buckets and times, leading to several electron bunches with different peak energies. To create single electron bunches with low energy spread, experiments using localized ionization injection inside a capillary discharge waveguide were performed. A single injected bunch with energy 1.6 GeV, charge 38 pC, divergence 1 mrad, and relative energy spread below 2% full-width half-maximum was produced in a 3.3 cm-long capillary discharge waveguide. This development shows promise for mitigation of energy spread and future high efficiency staged acceleration experiments.
关键词： capillary discharge,inverse Bremsstrahlung laser heating,electron acceleration,laser-driven plasma accelerator,plasma channel
更新于2025-09-23 15:21:01
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Local Overheating of Biotissue Labeled With Upconversion Nanoparticles Under Yb3+ Resonance Excitation
摘要： Local overheating of biotissue is a critical step for biomedical applications, such as photothermal therapy, enhancement of vascular permeability, remote control of drug release, and so on. Overheating of biological tissue when exposed to light is usually realized by utilizing the materials with a high-absorption cross section (gold, silica, carbon nanoparticles, etc.). Here, we demonstrate core/shell NaYF4:Yb3+, Tm3+/NaYF4 upconversion nanoparticles (UCNPs) commonly used for bioimaging as promising near-infrared (NIR) absorbers for local overheating of biotissue. We assume that achievable temperature of tissue labeled with nanoparticles is high enough because of Yb3+ resonance absorption of NIR radiation, whereas the use of auxiliary light-absorbing materials or shells is optional for photothermal therapy. For this purpose, a computational model of tissue heating based on the energy balance equations was developed and verified with the experimentally obtained thermal-graphic maps of a mouse in response to the 975-nm laser irradiation. Labeling of biotissue with UCNPs was found to increase the local temperature up to 2?C compared to that of the non-labeled area under the laser intensity lower than 1 W/cm2. The cellular response to the UCNP-initiated hyperthermia at subcritical ablation temperatures (lower than 42?C) was demonstrated by measuring the heat shock protein overexpression. This indicates that the absorption cross section of Yb3+ in UCNPs is relatively large, and microscopic temperature of nanoparticles exceeds the integral tissue temperature. In summary, a new approach based on the use of UCNP without any additional NIR absorbers was used to demonstrate a simple approach in the development of photoluminescent probes for simultaneous bioimaging and local hyperthermia.
关键词： near-infrared irradiation,local overheating,photothermal material,bioimaging,heat shock proteins,biotissue laser heating,hyperthermia,upconversion nanoparticles
更新于2025-09-23 15:21:01
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Lithium Pentazolate Synthesized by Laser Heating Compressed Lithium Azide and Nitrogen
摘要： Searching for polynitrogen compounds has attracted great attention due to their potential applications as high energy density materials. Here, we report a facile approach to the synthesis of solid lithium pentazolate (LiN5) compound by compressing lithium azide and molecular nitrogen under high pressure with laser heating. The formation of LiN5 with crystal structure P21/m-LiN5 was identified according to the appearance of the vibrational modes of N5ˉ rings in Raman spectra and synchrotron X-ray diffraction measurements under high pressure. The LiN5 remains stable down to 18.5 GPa upon decompression. The bond lengths in N5ˉ are between single bond and double bond length. This study indicates that the precursor can effectively tune the high pressure phase of pentazolate providing us an alternative route to synthesize polynitrogen compound with novel structure.
关键词： Lithium azide,Laser heating,High pressure,Nitrogen and Lithium pentazolate
更新于2025-09-23 15:21:01
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Petapascal Pressure Driven by Fast Isochoric Heating with a Multipicosecond Intense Laser Pulse
摘要： Fast isochoric laser heating is a scheme to heat matter with a relativistic intensity (> 1018 W=cm2) laser pulse for producing an ultrahigh-energy-density (UHED) state. We have demonstrated an efficient fast isochoric heating of a compressed dense plasma core with a multipicosecond kilojoule-class petawatt laser and an assistance of externally applied kilotesla magnetic fields for guiding fast electrons to the dense plasma. A UHED state of 2.2 PPa is achieved experimentally with 4.6 kJ of total laser energy that is one order of magnitude lower than the energy used in the conventional implosion scheme. A two-dimensional particle-in-cell simulation confirmed that diffusive heating from a laser-plasma interaction zone to the dense plasma plays an essential role to the efficient creation of the UHED state.
关键词： magnetized fast isochoric heating,petapascal pressure,Fast isochoric laser heating,ultrahigh-energy-density state,multipicosecond intense laser pulse
更新于2025-09-23 15:19:57
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Transition regime in the ultrafast laser heating of solids
摘要： Based on the phenomenological theory of heat diffusion, we show that the generated peak temperature Tmax after absorption of a laser pulse strongly depends on the pulse duration. We identify three different heat conduction regimes that can be identified via a simple parameter that depends only on the pulse duration and on material constants. The phenomenological approach is supported by numerical simulations of heat diffusion and measurements of the thermal surface expansion after transient grating excitation with 1 ps and 10 ns optical pulses.
关键词： laser heating,heat diffusion,thermal surface expansion,pulse duration
更新于2025-09-23 15:19:57
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Nanosecond laser irradiation of soot particles: insights on structure and optical properties
摘要： In spite of the advances in laser diagnostics in combustion, the effect of rapid laser irradiation on the physical/chemical properties of soot particles is far from being comprehensively understood. Optical properties, particle nanostructure and aggregate size of laser-irradiated soot particles are analyzed in this paper. Carbonaceous particles sampled from nitrogen-quenched diffusion flames of ethylene and methane are irradiated on-line by a 1064-nm short laser pulse. Wavelength-resolved extinction measurements in the visible range are used to follow their transformation by varying the laser energy density. A variation of the extinction coefficient of the irradiated particles compared to the extinction coefficient of the pristine ones is observed, especially for ethylene soot. The particle nanostructures are analyzed by Raman spectroscopy and the effect of laser irradiation on aggregate structure is evaluated by measuring particle size distributions. The results indicate that both soot nanostructure and optical properties are strongly dependent on the laser energy density when irradiated by a laser source. This is significant for ethylene soot, while for methane soot the degree of variation of such properties is less pronounced, at least in the investigated heating conditions.
关键词： Raman spectroscopy,optical properties,laser-heating,Soot,nanostructure,LII
更新于2025-09-19 17:13:59
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Table-top nuclear magnetic resonance system for high-pressure studies with <i>in situ</i> laser heating
摘要： High pressure Nuclear Magnetic Resonance (NMR) is known to reveal the behavior of matter under extreme conditions. However, until now, significant maintenance demands, space requirements, and high costs of superconducting magnets render its application unfeasible for regular modern high pressure laboratories. Here, we present a table-top NMR system based on permanent Halbach magnet arrays with a diameter of 25 cm and height of 4 cm. At the highest field of 1013 mT, 1H-NMR spectra of ice VII have been recorded at 25 GPa and ambient temperature. The table-top NMR system can be used together with double sided laser heating setups. Feasibility of high-pressure high-temperature NMR was demonstrated by collecting 1H-NMR spectra of H2O at 25 GPa and 1063(50) K. The change in the signal intensity in a laser-heated NMR diamond anvil cell has been found to yield a convenient way for temperature measurements.
关键词： diamond anvil cell,laser heating,Halbach magnet,Nuclear Magnetic Resonance,high-pressure
更新于2025-09-16 10:30:52
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Analysis of the Heat Affected Zone and Surface Roughness during Laser Micromachining of Metals
摘要： The current research focuses on the characterization of the produced heat affected zone when laser heats AISI H13 steel, AISI 1045 steel and Ti6Al4V alloy workpieces via finite element simulations and experimental investigation. The surface roughness designedly varies on the surface of the samples and its influence on the absorption of laser light is investigated. Experiments are conducted at 1-4 W laser power and for two scanning speeds of 2 and 100 mm/min. A 3D transient thermo-structural finite element model for a moving Gaussian laser heat source is developed to simulate the micromachining process and predict the depth and width of the heat affected zone. The Johnson-Cook material model that takes into account the effect of plastic strain, strain rate and temperature, along with a fracture model, is adapted to the simulations. A good agreement between the experimental data and the simulation results is found. The depth and width of the heat affected zone strongly depend on the laser parameters and material properties of the irradiated samples. This study constitutes the basis to the optimization and improvement of the laser assisted micromachining process parameters and provides key insights on the roughness-absorptivity relation for the three metallic materials.
关键词： finite element method,heat affecting zone,white-light interferometry,laser heating
更新于2025-09-16 10:30:52
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Laser heating setup for diamond anvil cells for <i>in situ</i> synchrotron and in house high and ultra-high pressure studies
摘要： The diamond anvil cell (DAC) technique combined with laser heating is one of the major methods for studying materials at high pressure and high temperature conditions. In this work, we present a transferable double-sided laser heating setup for DACs with in situ temperature determination. The setup allows precise heating of samples inside a DAC at pressures above 200 GPa and could be combined with synchrotron beamline equipment. It can be applied to X-ray diffraction and X-ray transmission microscopy experiments. In the setup, we use high-magnification and low working distance infinity corrected laser focusing objectives that enable us to decrease the size of the laser beam to less than 5 μm and achieve the maximum optical magnification of 320 times. All optical components of the setup were chosen to minimize chromatic and spatial aberrations for accurate in situ temperature determination by multiwavelength spectroscopy in the 570–830 nm spectral range. Flexible design of our setup allows simple interchange of laser sources and focusing optics for application in different types of studies. The setup was successfully tested in house and at the high-pressure diffraction beamline ID15B at the European Synchrotron Radiation Facility. We demonstrate an example of application of the setup for the high pressure–high temperature powder diffraction study of PdH and X-ray transmission microscopy of platinum at 22(1) GPa as a novel method of melting detection in DACs.
关键词： high pressure,diamond anvil cell,X-ray transmission microscopy,X-ray diffraction,synchrotron,laser heating,high temperature
更新于2025-09-16 10:30:52