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Real-time adjustable, 11 <i>μ</i> s FWHM, >5 kHz, piezo electric pulsed atomic beam source
摘要： This paper provides a detailed description of how to construct a pulsed atomic beam source [including a fast ionization gauge (FIG) for characterization] with a unique combination of characteristics. We include technical drawings for a real-time adjustable piezo electric actuated pulsed valve capable of generating a 11 μs duration pulse of gas at a repetition rate of >5 KHz, with a shot-to-shot stability of 0.6%, and maximum densities of 1015 particles/cm3. We also include details on how to construct a FIG, with a 4 μs rise time, to measure the pulse. We report a 3D density map of a supersonic expansion of helium gas with a speed ratio S = 46 and a calculated longitudinal temperature of 0.3 K. Finally, the results of a laser ionization test are provided in order to verify the performance of the pulsed valve in a typical experimental configuration.
关键词： fast ionization gauge,piezo electric pulsed atomic beam source,supersonic expansion,laser ionization
更新于2025-09-23 15:21:01
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Qualitative and Quantitative Distinction of <i>ortho</i> -, <i>meta</i> -, and <i>para</i> -Fluorotoluene by Means of Chirped Femtosecond Laser Ionization
摘要： Femtosecond-laser ionization mass spectrometry (fs-LIMS) is demonstrated to be a powerful analytical method providing access to the qualitative distinction of structural isomers of ortho-, meta-, and para-fluorotoluene. The key point of the approach presented is a systematic variation of the spectral phase of the fs-laser pulses, which characteristically affects the fragmentation pattern observed in the mass spectra. Variation of the linear chirp parameter is also helpful for rationalizing the fragmentation mechanism. Ultimately two ternary mixtures of the three title isomers are quantitatively analyzed in situ with an accuracy of 5% for the molar fractions.
关键词： structural isomers,Femtosecond-laser ionization mass spectrometry,fragmentation pattern,spectral phase,quantitative analysis,fluorotoluene
更新于2025-09-23 15:19:57
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Transport of ultraintense laser-driven relativistic electrons in dielectric targets
摘要： Ultraintense laser-driven relativistic electrons provide a way of heating matter to high energy density states related to many applications. However, the transport of relativistic electrons in solid targets has not been understood well yet, especially in dielectric targets. We present the ?rst detailed two-dimensional particle-in-cell simulations of relativistic electron transport in a silicon target by including the ?eld ionization and collisional ionization processes. An ionization wave is found propagating in the insulator, with a velocity dependent on laser intensity and slower than the relativistic electron velocity. Widely spread electric ?elds in front of the sheath ?elds are observed due to the collective effect of free electrons and ions. The electric ?elds are much weaker than the threshold electric ?eld of ?eld ionization. Two-stream instability behind the ionization front arises for the cases with laser intensity greater than 5 × 1019 W/cm2 that produce high relativistic electron current densities.
关键词： transport,ultraintense laser,ionization wave,relativistic electrons
更新于2025-09-23 15:19:57
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Ionization and acceleration of multiply charged gold ions in solid film irradiated by high intensity laser
摘要： In this paper, we present the mechanisms of ionization of a thin gold ?lm irradiated by a high-intensity, short-pulse laser in the range of I ? 1020(cid:2)22 W=cm2 and the associated acceleration of multiply charged gold ions. A numerical one-dimensional simulation using an extended particle-in-cell code, which includes atomic and collisional relaxation processes, indicates that two types of acceleration, hole-boring radiation pressure acceleration (RPA) and target normal sheath acceleration (TNSA), contribute to the generation of highly charged ions with kinetic energies on the order of 10 MeV/u. In each acceleration, a longitudinal electrostatic ?eld excited by different mechanisms dominantly ionizes atoms to higher charge states and accelerates them to the vacuum region from the rear surface, which is opposite the front surface irradiated by the laser ?eld. The ?eld ionization process dominantly ionizes high energy ions to the high charge state, while a large number of ions with energy <1 MeV=u are ionized by an electron impact ionization process. In TNSA, a multiply charged ion generated at the rear surface is accelerated to the maximum energy although the ion with the highest charge state is generated at the front surface in RPA. However, the existence of contamination, such as water vapor, suppresses the ion energy of TNSA to less than that of RPA since the sheath ?eld readily accelerates the protons and oxygen prior to the acceleration of the gold ions. Our derived theoretical scaling describes the maximum ion energy for each charge state in the cases with and without contamination using the relationship between the longitudinal electrostatic ?eld pro?le near the rear surface and the classical tunnel ?eld ionization model.
关键词： acceleration,multiply charged gold ions,RPA,TNSA,high-intensity laser,ionization,solid film
更新于2025-09-23 15:19:57
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A Simple Method for the Evaluation of the Pulse Width of an Ultraviolet Femtosecond Laser Used in Two-Photon Ionization Mass Spectrometry
摘要： A simple method was proposed for on-site evaluation of the pulse width of an ultraviolet femtosecond laser coupled with a mass spectrometer. This technique was based on measurement of a two-photon ionization signal in mass spectrometry by translation of the prism in the pulse compressor of the femtosecond laser. The method was applied to optical pulses that were emitted at wavelengths of 267, 241, and 219 nm; the latter two pulses were generated by four-wave Raman mixing using the third harmonic emission of a Ti:sapphire laser (267 nm) in hydrogen gas. The measurement results show that this approach is useful for evaluation of the pulse width of the ultraviolet femtosecond laser used in mass spectrometry for trace analysis of organic compounds.
关键词： pulse width,mass spectrometry,ultraviolet femtosecond laser,ionization
更新于2025-09-23 15:19:57
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Laser ionization ion mobility spectrometric interrogation of acoustically levitated droplets
摘要： Acoustically levitated droplets have been suggested as compartmentalized, yet wall-less microreactors for high-throughput reaction optimization purposes. The absence of walls is envisioned to simplify up-scaling of the optimized reaction conditions found in the microliter volumes. A consequent pursuance of high-throughput chemistry calls for a fast, robust and sensitive analysis suited for online interrogation. For reaction optimization, targeted analysis with relatively low sensitivity suffices, while a fast, robust and automated sampling is paramount. To follow this approach, in this contribution, a direct coupling of levitated droplets to a homebuilt ion mobility spectrometer (IMS) is presented. The sampling, transfer to the gas phase, as well as the ionization are all performed by a single exposure of the sampling volume to the resonant output of a mid-IR laser. Once formed, the nascent spatially and temporally evolving analyte ion cloud needs to be guided out of the acoustically confined trap into the inlet of the ion mobility spectrometer. Since the IMS is operated at ambient pressure, no fluid dynamic along a pressure gradient can be employed. Instead, the transfer is achieved by the electrostatic potential gradient inside a dual ring electrode ion optics, guiding the analyte ion cloud into the first stage of the IMS linear drift tube accelerator. The design of the appropriate atmospheric pressure ion optics is based on the original vacuum ion optics design of Wiley and McLaren. The obtained experimental results nicely coincide with ion trajectory calculations based on a collisional model.
关键词： Ion mobility spectrometry,Acoustic levitation,Ambient pressure laser ionization,Ion optics
更新于2025-09-16 10:30:52
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A new control system for high-precision In-Gas Laser Ionization and Spectroscopy experiments at KU Leuven
摘要： A new automated control system is developed for the In-Gas Laser Ionization and Spectroscopy (IGLIS) laboratory at KU Leuven. The IGLIS Control System is capable of stabilizing a narrowband single-mode tunable diode laser with a standard deviation of 1.14 MHz. Furthermore, the system controls and synchronizes all data acquisition for multiple techniques from resonant laser spectroscopy in gas cell or in gas jet to atomic Planar-Laser Induced Fluorescence (PLIF) spectroscopy of copper atoms seeded in a supersonic gas jet. The IGLIS Control System is validated by measuring the hyperfine splitting parameters of the ground state transition at 327 nm in 63Cu.
关键词： Laser spectroscopy,In-Gas-Jet Laser Ionization and Spectroscopy,Data acquisition
更新于2025-09-12 10:27:22
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Atom beam emersion from hot cavity laser ion sources
摘要： Ion sources exploiting laser resonance ionization offer efficient and element-selective radioactive ion beam production at the leading isotope separation on-line facilities worldwide. Most commonly, laser resonance ionization takes place inside a resistively heated atomizer tube directly coupled to the production target, where the element of interest is evaporated and provided as atomic vapor. While naturally the majority of atoms is ionized inside this hot cavity, a fraction of the neutrals effuses towards the high voltage beam extraction system of the subsequent mass separator. We report on several systematic investigations on this phenomenon regarding its significance and implications on the operation of resonance ionization laser ion sources. Experiments suggest a less sharply directed atom cone than expected from theoretical model, up to a lateral opening angle of 45°. Inside the tubular volume defined by the laser beam diameter around the central axis behind the source exit, more than 90% of potentially ionizable atoms are found within the first 2 cm. Geometrical constraints for the construction of devices based on ionization in the effusing atom beam directly downstream of the hot cavity are derived, and causes for cross-mass beam contamination are identified. Counter measures using laser repetition rate synchronized beam gating by fast electrostatic beam deflection to overcome these problems are presented.
关键词： Laser ion source,ISOLDE,Mass separation,Resonance laser ionization,Atom effusion,Ion source development
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - THz Emission Driven by Ionization Pressure in Relativistic Plasmas
摘要： The ability of terahertz (THz) waves to probe matter is attracting wide interest for applications in, e.g., remote spectroscopy. For this purpose, high field strengths with broad bandwidths are requested, which can be supplied by gas plasmas created by two-color ultrashort laser pulses [1]. With moderate intensities ～ 1014 W/cm2, intense light pulses composed of a 800-nm fundamental wavelength and its second harmonic achieve THz conversion efficiency of ～ 10?4 through photocurrents [2]. In the relativistic regime, i.e., when the normalized laser vector potential a0 is larger than unity, plasma waves trigger a strong longitudinal field exploited for laser-wakefield electron acceleration (LWFA). The electron bunch then acts as a THz emitting source from coherent transition radiation (CTR) initiated at the plasma-vacuum interface, which may provide larger conversion efficiencies > 5 × 10?3 [3]. On the other hand, mid- and far-infrared light sources operating at TW powers are nowadays available. In particular, CO2 (10.6 μm) lasers are operational in the picosecond regime and their technology, rapidly evolving to the 100 TW level [4], will soon offer revolutionary sources for studying novel regimes in particle acceleration. Here we report a new mechanism for THz field generation induced by ultrashort long-wavelength pulses interacting with gases, namely, the photon downshift enhanced by ionization pressure (IP), which differs from the classical photocurrents (PC). With far-infrared laser pumps, the ionization fronts cause a drastic enhancement of the plasma waves through ionization-induced ponderomotive force and pulse steepening, which leads to a strong redshift in the laser spectrum and amplify THz components mediated by stimulated Raman scattering (SRS). Numerical simulations are performed with a 2D particle-in-cell code for the two fundamental wavelengths λ0 ≡ 2πc/ω0 = 0.8 and 10.6 μm using the normalized field a0 = 2.2 that interacts with a helium gas of atomic density 5.5 × 1017 cm?3. The laser pulse is Gaussian with its two harmonics (ω0, 2ω0) having the same FWHM duration (τ0 = 150 fs). It evolves through a 250-μm-long plasma in the self-modulated-LWFA regime for which the plasma wavelength λp = 32 μm is smaller than the pulse length cτ0. This regime allows to drive a large-amplitude plasma wave that strongly couples with the laser field and downshifts the laser frequency towards much smaller ones via forward SRS. This downconversion process is all the more augmented through IP that more photoionization sequences are triggered. It directly broadens the radiated wave spectrum to the frequency range ≤ 10 THz yielding 20 GV/m THz pulses with conversion efficiency of 1.2% [Fig. 1(a)], without any need to tailor the density profile as recently proposed in [5]. In addition, an efficient CTR driven by electron injection gives rise to a strong axisymmetric THz field (1.4% conversion efficiency) polarized in the radial direction [Fig. 1(b)].
关键词： photocurrents,stimulated Raman scattering,laser,ionization pressure,terahertz,plasma
更新于2025-09-12 10:27:22
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Efficient two-color two-step laser ionization schemes of λ <sub/>1</sub> ～ 250 nm and λ <sub/>2</sub> = 307.9 nm for heavy refractory elements—Measurements of ionization cross-sections and hyperfine spectra of tantalum and tungsten
摘要： We demonstrated efficient two-color two-step laser ionization schemes in the combined use of λ1 ～ 250 nm and λ2 = 307.9 nm, which are applicable to heavy refractory elements with an atomic number in the wide range of Z = 69–78. We investigated newly observed ionization schemes of tantalum and tungsten atoms in an argon-gas-cell-based laser ion source for the efficient ionization of atoms of unstable nuclei through the two-color two-step laser resonance ionization technique. We experimentally determined the ionization cross sections from the measured saturation curves by solving the rate equations for the ground, intermediate, and ionization continuum populations. Hyperfine structures of these elements were also studied to deduce the isotope-shift, pressure-shift, and pressure-broadening in the resonance spectra of the excitation transitions in the argon gas cell. The electronic factor F255 of the excitation transition λ1 = 255.2115 nm between the ground and intermediate states was deduced from the measured isotope shifts of stable 182,183,184,186W isotopes. The ionization schemes investigated here are applicable to extract any isotopes of these elements by considering the measured pressure shift and nuclear isotope shift in optimizing the wavelength λ1.
关键词： ionization cross-sections,laser ionization,tantalum,hyperfine spectra,tungsten
更新于2025-09-11 14:15:04