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Cooper minimum of high-order harmonic spectra from an MgO crystal in an ultrashort laser pulse
摘要： Cooper minimum structure of high-order harmonic spectra from atoms or molecules has been extensively studied. In this paper, we demonstrate that the crystal harmonic spectra from an ultrashort midinfrared laser pulse also exhibit the Cooper minimum characteristic. Based on the accurate band dispersion and k-dependent transition dipole moment (TDM) from the ?rst-principles calculations, it can be found that the harmonic spectra from the MgO crystal along the (cid:2)-X direction present a dip structure in the plateau, which is originated from the valley of TDM by examining the distribution of the harmonic intensity at the k space. The Cooper minimum feature in crystal high-order-harmonic generation (HHG) will pave a new way to retrieve the band information of solid materials by using HHG from the ultrashort midinfrared laser pulse.
关键词： transition dipole moment,ultrashort laser pulse,Cooper minimum,MgO crystal,high-order harmonic generation
更新于2025-09-23 15:21:01
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Stages of the Excitation Relaxation in a Superconductor after the Impact of a Femtosecond Laser Pulse Taking into Account the Momentum Distribution of Quasiparticles
摘要： A theoretical model is formulated for the description of the nonequilibrium state of a superconductor on the basis of the nonequilibrium distribution function of phonons and quasiparticles on a finite momentum lattice convenient for numerical simulation. The simulation is performed under conditions of pulsed optical impact demonstrating the role of excess quasiparticles in suppressing the order parameter and the main stages of the relaxation process in the absence of electric current.
关键词： superconductivity,kinetics simulation,nonequilibrium processes,ultrashort laser pulse
更新于2025-09-23 15:21:01
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Formation of Quantum Vortices at the Ionization of an Atom by an Ultrashort Laser Pulse: Two- and Three-Dimensional Cases
摘要： Quantum vortices formed at the barrier-suppression ionization of an atom by an ultrashort laser pulse have been studied theoretically and numerically. The ionization of a hydrogen atom is considered in the two-dimensional space and the ionization of an atom in the zero-range potential approximation is considered in the three-dimensional space. The resulting analytical expressions imply that the localization of quantum vortices in the three-dimensional space can be predicted by analyzing the two-dimensional model.
关键词： hydrogen atom,zero-range potential approximation,ultrashort laser pulse,Quantum vortices,barrier-suppression ionization
更新于2025-09-23 15:19:57
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Optimization of laser parameters for proton acceleration using double laser pulses in TNSA mechanism
摘要： The energy of protons accelerated by ultra-intense lasers in the target normal sheath acceleration (TNSA) mechanism can be greatly enhanced by the laser parameter optimization. We propose to investigate the optimization of laser parameters for proton acceleration using double laser pulses in TNSA mechanism. The sheath field generation at the rear side of the target is significantly affected by the introduction of second laser pulse in TNSA mechanism, and consequently, the energy of the accelerated protons is also modified. The second laser pulse was introduced with different delays to study its impact on proton acceleration. Our study shows that the interplay of laser intensity and pulse duration of both laser pulses affects the proton acceleration. It was found that the proton maximum energy is the function of both laser intensity and pulse duration. A number of simulations have been performed to obtain maximum proton energy data under different combinations of laser intensity and pulse duration for the two laser pulses. The simulation results account for the underline physics for the proton bunch energy and the sheath field as a function of pulse intensity and pulse delay.
关键词： proton acceleration,ultrashort laser pulse,Laser–plasma interaction
更新于2025-09-16 10:30:52
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Adiabatic Vlasov theory of ultrastrong femtosecond laser pulse propagation in plasma. The scaling of ultrarelativistic quasi-stationary states: spikes, peakons, and bubbles
摘要： The interaction of an ultrashort (femtosecond), pancake-shaped laser pulse with underdense unmagnetized plasma is studied analytically and numerically in a regime with ultrarelativistic electron jitter velocities. The adiabatic evolution of the quasistationary electron distribution function is resolved by following particles along their nonlinear trajectories in phase space. It is estimated that under typical laser-plasma accelerator conditions, the quasistationary distribution is established after the pulse has penetrated ≈1 mm into the plasma. The main particle effect is found to be the beam loading associated with the electrons reflected from the maxima of the effective potential, a fraction of which can also be entrapped in the time dependent potential minima. Owing to the relativistic mass increase, their participation in the plasma dynamics is reduced. The number density of reflected particles is exponentially small for nonrelativistic electron temperatures, but at the wavebreak, it can become comparable to the density of the background plasma if the temperature of electrons exceeds several percent of their rest energy m0c2. Numerical calculations in the presence of beam loading and in the strong intensity regime, based on the three-time scale approximation[Jovanovic′ et al., Phys. Plasmas 22, 043110.1 (2015)], reveal the creation of a bubble in the electron density, along with the steepening and the breaking of the nonlinear Langmuir wake that occurs simultaneously with the creation of a sharp spike in the distribution function and a peak in the electron density, located at the position of the wavebreak.
关键词： plasma,beam loading,ultrarelativistic electron jitter velocities,ultrashort laser pulse,wavebreak,adiabatic evolution
更新于2025-09-16 10:30:52
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Helical drilling of three-dimensional conical converging-diverging nozzle in steel using ultrashort laser pulses
摘要： Three-dimensional conical converging-diverging nozzle typically a de Laval nozzle can be used for micropropulsion of microsatellites. The profile control, surface roughness and symmetry of the nozzle are key parameters to determine its performance. In this paper, we focus on the fabrication of a three-dimensional conical converging-diverging nozzle using helical drilling optics and ultrashort laser pulses. The helical optics makes it possible to dynamically control the profile of a hole by adapting the helical path during drilling process. An opening angle up to 18.6° on the converging part and 6.6° on the diverging part are achievable in 1 mm thick stainless steel by means of classic helical drilling. By introducing a dynamic helical process, the opening angle of converging part with straight profile can be extended to more than 90°. Moreover, the employment of an ultrashort pulsed laser has contributed to a high quality surface on the hole-wall having an average roughness less than 0.4 μm.
关键词： nozzle fabrication,ultrashort laser pulse,helical path,Helical drilling optics,shaped holes
更新于2025-09-12 10:27:22
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Non-Markovian pure dephasing in a dielectric excited by a few-cycle laser pulse
摘要： We develop the theory of pure dephasing in a solid exposed to an ultrashort laser pulse beyond the commonly used Markov approximation. This approach takes into account the finite cutoff energy of the bath and can be applied to both many-particle and phonon environments. With numerical simulations performed with the time-dependent Hartree-Fock equations, we investigate how the excitation probability and high-harmonic generation are described by different models of decoherence. It is shown that the time-dependent rates allow for temporally high dephasing to successfully reproduce the main features of high-harmonics spectrum and avoid an overestimation of the charge carrier population after the pulse, which is a common problem of the Markov approximation.
关键词： pure dephasing,time-dependent Hartree-Fock,non-Markovian,ultrashort laser pulse,high-harmonic generation
更新于2025-09-11 14:15:04