The European Physical Journal D最新文献

This study explores the potential for high-harmonic generation (HHG) from argon atomic gas and single attosecond pulse generation by leveraging amplified and hyper-focused short laser pulses through a plasmonic nanostructure. The plasmonic nanostructure features triangular nanobowties with multilayer compositions of dielectrics and metals, supported by an insulating substrate. Within the nanobowtie gap, localized surface plasmons significantly enhance the laser field intensity over a substantial volume of the gap. Fine-tuning the geometric parameters of this structure achieves up to 45-fold amplification (< 17 dB) within the central wavelength of 800 nm of a standard titanium–sapphire laser. This enhancement enables the argon atoms introduced via a gas jet to exhibit a pronounced nonlinear response, leading to high-intensity HHG under incident pulses of relatively low intensity (10¹² W/cm²). Based on the harmonic spectrum observed, the generation of isolated attosecond pulses with a temporal width of 33.37 attoseconds is achievable, notably without necessitating chirp mitigation techniques.

Graphical abstract

The behavior of toroidal and poloidal rotations in the edge region is studied in the presence of locked m/n = 2/1 and m/n = 3/1 magnetic islands, excited by Resonant Magnetic Perturbations (RMPs) on the J-TEXT tokamak. When the 2/1 magnetic island is present, a significant change in the toroidal rotation of carbon V (C⁴⁺) is observed, with the reversing from the counter-current to the co-current direction. In contrast, the 3/1 magnetic island has a weaker effect on C⁴⁺ rotation but strongly influences the rotation of carbon III (C²⁺), which is closer to the 3/1 island. RMP phase scans show that the toroidal rotation change of C²⁺ increases as it approaches the O-point of the magnetic island. This region corresponds to a more positive radial electric field E_r on the outer side of the 3/1 magnetic island, as measured by electric probes.

Graphical abstract

Evolution of CV toroidal rotation measured by different viewing channels when 2/1 magnetic islands are induced at different phases

Evolutions of C III toroidal rotation under different RMP phases measured from 2 different directions when 3/1 magnetic islands are induced at different phases. Red solid line represent measurement from counter-I_p direction and blue represent co-I_p direction

This paper presents a study of the phase sensitivity of the transparency and absorption when a microwave (MW) field connects the two ground energy levels of a four-level N-type configuration. This four-level N-type system can be considered with the hyperfine energy levels of the D₁ and/or D₂ lines of ⁸⁷Rb atoms. The effect of the MW field on electromagnetically induced transparency (EIT) and on absorption (EIA) is investigated in a weak pump region. Furthermore, we demonstrate that a small absorption dip appears on the top of the EIT in the strong probe region and the absorption dip gradually increases with the increasing value of the MW field at a specific off-detuning position of the pump laser field. The optical Bloch equations for the four-level N-type system are derived and the equations are solved numerically to obtain the results under steady state condition. Additionally, we show that by adjusting the phase of the MW field, a narrow EIT or EIA feature is converted into Autler–Townes Splitting (ATS) under the strong pump conditions.

Graphical abstract

As is well known, the spontaneous emission of atoms is influenced by the electromagnetic environment. In this work, we resort to a special Hyperbolic Metamaterial (HMM), named as the linear cross metamaterial (LCMM). The isofrequency wavevector surface of the LCMM exhibits a biconical shape with linear dispersion, which holds great promise for a variety of applications. Furthermore, LCMM combined squares displays more unique electromagnetic characteristics, where electromagnetic waves form an energy flow loop. Using the finite-difference time-domain (FDTD) method, we calculate the SpE rate of atom through the radiative energy fluxes of a corresponding dipole. The results show that LCMM and LCMM combined squares have a large degree of freedom to control the SpE rate of atoms, and have high anisotropy that is conducive to quantum interference of three-level atoms. These results provide valuable insights into the mechanisms of LCMM and contribute to the design of novel tunable devices for future applications.

Graphical abstract

Electron beam lithography (EBL) is a prominent technique for fabricating nanostructures with exceptional precision, owing to its capability to manipulate electron beams at the nanoscale. This study presents the design and development of a miniaturized optical column capable of producing electron beams with diameters on the order of a few nanometers, specifically tailored for advanced lithographic applications. The system integrates an electron gun and an electrostatic Einzel lens to focus the electron beam onto material surfaces effectively. Notably, compact design achieves a size comparable to that of a human finger, facilitating its use in practical miniature devices. Through the systematic analysis, the optimal kinetic energy for electron emission was determined to be below 10⁻⁶ eV, while the focal electrode of the electrostatic lens was optimally biased at approximately 100 kV. Geometric parameters of the Einzel lens were refined, including adjusting the distance between the lens and the electron gun, to minimize the electron beam diameter and enhance focusing performance. Additionally, the impact of increasing the length of the iron shroud surrounding the final electrode was examined. Results indicate that extending the iron shroud reduces the optical column aperture, intensifying the lens’s electric field concentration. This modification shifts the beam’s focal point closer to the column but also increases the diameter of the electron beam at the focus. These findings contribute to developing compact, high-resolution EBL systems with potential for diverse nanofabrication applications.

Graphical abstract

The first ionization threshold and the appearance energies of the ion fragments of xylitol (C₅H₁₂O₅) and sorbitol (C₆H₁₄O₆) molecules have been measured using a mass spectrometry method. The total ionization cross sections of these species have also been measured due to electron impact. Additionally, the structure and the molecular orbitals (MOs) of the D- and L-isomers of xylitol and sorbitol have been calculated using the Hartree–Fock (HF) and density functional theory (DFT) methods. The MO properties have been used then to determine the absolute total single ionization cross sections from the Binary-Encounter-Bethe and Grizinsky models. The measured first ionization energies of xylitol and sorbitol are 10.41 ± 0.25 eV and 10.35 ± 0.25 eV. They were also estimated from the binding energies of the HOMO orbital and calculated in the adiabatic approximation from the ab initio total energies. The experimental cross sections have been normalized to the corresponding data from the Grizinsky model at near-threshold energies, where the ionization is mostly driven by the contribution from the highest occupied orbitals.

Graphical abstract