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Application of the saddle-point method to strong-laser-field ionization
摘要： The quantum-mechanical transition amplitude of an ionization process induced by a strong laser field is typically expressed in the form of an integral over the ionization time of a highly oscillatory function. Within the saddle-point (SP) approximation this integral can be represented by a sum over the contributions of the solutions of the SP equation for complex ionization time. It is shown that, for the general case of an elliptically polarized polychromatic laser field, these solutions can be obtained as zeros of a trigonometric polynomial of the order n and that there are exactly n relevant solutions, which are to be included in the sum. The results obtained are illustrated by examples of various tailored laser fields that are presently used in strong-field physics and attoscience. For some critical values of the parameters two SP solutions can coalesce and the topology of the ‘steepest descent’ integration contour changes so that some SPs are bypassed. Around the critical parameters a uniform approximation should be used instead of the SP method.
关键词： attoscience,elliptically polarized polychromatic laser field,strong-laser-field ionization,quantum-mechanical transition amplitude,saddle-point method
更新于2025-09-16 10:30:52
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The transition from double to single quantum dot induced by THz laser field
摘要： The combined influence of an intense laser field and a homogeneous magnetic field is considered on laterally coupled double quantum dot with isotropic and anisotropic parabolic confinement. It is shown that intense laser field can recover typical properties to a single quantum dot: it creates Fock–Darwin states in a double quantum dot with anisotropic confinement. Also, the laser and the magnetic field effects on the intraband absorption spectrum reveal blueshift if the laser field is increased and redshift with the gain of the magnetic field.
关键词： Double quantum dot,Fock–Darwin states,Intense laser field,Magnetic field,Intraband absorption
更新于2025-09-16 10:30:52
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Oscillator strength and carrier dynamics in type I and inverted type I spherical core/ shell nanostructures under external laser field
摘要： For the first time, the effect of laser on the donor impurity states in spherical nano core/ shell systems is examined theoretically by variation technique. In this work, a step like laser dressed confinement potential is employed to evolve the donor dynamics in two different spherical core/ shell quantum structures namely (a) Type I GaAs/ Al0.3Ga0.7As core shell nanostructure (CSN) and (b) Inverted Type I Al0.3Ga0.7As/ GaAs CSN. Donor binding energy (BE) is calculated for various laser dressing parameter (α0) for various impurity locations (Ri) by varying the dimensions of the systems. Effect of laser on sub-level energy (E0), oscillator strength (P10), transition energy (E10) and the magnitude of dipole matrix element (|M10|) of the systems are also determined. The diverse behavior of type I and inverted type I CSNs are analyzed. It is witnessed that in type I the carrier is highly confined whereas inverted type I favors tunneling. This study will help in understanding the influence of laser field on donor impurity in CSNs and its application towards optical devices.
关键词： Type I core/shell,Laser field,Donor Binding,Oscillator Strength,Inverted Type I core/shell
更新于2025-09-16 10:30:52
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High-energy bremsstrahlung on atoms in a laser field
摘要： The impact of a laser field on the process of photon radiation by an ultra-relativistic electron in an atomic field is investigated. The angular distribution and the spectrum of the radiated photon are derived. By means of the quasiclassical approximation, the obtained results are exact in the parameters of the laser field and the atomic field. It is shown that the impact of the laser field is significant even for fairly average values of the laser field parameters routinely achievable nowadays. Therefore, an experimental observation of the influence of the laser field on bremsstrahlung in the atomic field is a very feasible task.
关键词： quasiclassical approximation,photon radiation,bremsstrahlung,atomic field,laser field
更新于2025-09-12 10:27:22
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Spatial Characteristics of Thomson Scattering Spectra in Laser and Magnetic Fields
摘要： Spatial characteristics of Thomson scattering spectra are studied for an electron moving in the circularly polarized laser field in the presence of a strong uniform magnetic field. The results show that the angular distributions of the spectra with respect to the azimuthal and polar angles exhibit different symmetries, respectively, which depend on the fields and electron parameters sensitively and significantly. Moreover, for relatively large parameters such as high laser intensity, high magnetic resonance parameter as well as large initial momentum of electron, the two lobes in spectra tend to the laser-propagating direction so that the radiation can be collimated in the forward direction. Furthermore, an important finding is that by choosing the appropriate fields and initial momentum of electron, the high frequency part of the Thomson scattering spectra can reach the frequency range of soft x-ray, in which a high radiation power per solid angle as ～1011 a.u. can be obtained.
关键词： Thomson scattering,magnetic field,spatial characteristics,laser field,soft x-ray
更新于2025-09-12 10:27:22
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Attosecond Pulse Amplification in a Plasma-Based X-Ray Laser Dressed by an Infrared Laser Field
摘要： High-harmonic generation (HHG) of laser radiation has led to attosecond pulse formation which offers unprecedented temporal resolution in observing and controlling electron and nuclear dynamics. But the energy of attosecond pulses remains quite small, especially for photon energies exceeding 100 eV, which limits their practical applications. We propose a method for amplification of attosecond pulses in the active medium of a plasma-based x-ray laser dressed by a replica of the laser field used for HHG. The experimental implementation is suggested in hydrogenlike C5t x-ray laser at 3.4 nm wavelength in the “water window” range.
关键词： attosecond pulse amplification,infrared laser field,plasma-based x-ray laser,high-harmonic generation,water window
更新于2025-09-12 10:27:22
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Relative phase effect of nonsequential double ionization in Ar by two-color elliptically polarized laser field
摘要： We investigated the nonsequential double ionization (NSDI) in Ar by two-color elliptically polarized laser field with a 3D classical ensemble method. We study the relative phase effect of NSDI and distinguish two particular recollision channels in NSDI, which are recollision-impact ionization (RII) and recollision-induced excitation with subsequent ionization (RESI), according to the delay-time between the recollision and the final double ionization. The numerical results indicate that the ion momentum distribution is changed and the triangle structure is more obvious with the decrease of the relative phase. We also demonstrate that the RESI process always dominates in the whole double ionization process and the ratio of the RESI and RII channel can be influenced by the relative phase.
关键词： nonsequential double ionization,recollision-induced excitation with subsequent ionization,two-color elliptically polarized laser field,recollision-impact ionization
更新于2025-09-12 10:27:22
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Effective tuning of isotropic and anisotropic properties of quantum dots and rings by external fields
摘要： The combined effects of intense THz laser field, magnetic field and in-plane electric field on electronic states and intraband optical properties of single isotropic quantum dots and rings are investigated using the non-perturbative Floquet theory in the high-frequency limit. Here we show that the change of the electric field direction for fixed values of intense THz laser field parameter can recover the degeneracy of the excited states and the dipole-allowed transition intensities in a quantum dot. Additionally, it is shown that in isotropic quantum rings the intense THz laser and the in-plane electric field create unusual Aharonov-Bohm oscillations. For fixed values of the intense THz laser field parameter, the amplitudes of Aharonov-Bohm oscillations can be effectively tuned by changing the electric field direction. Furthermore, for fixed values of the electric field strength and the laser field parameter the intraband optical properties can be effectively tuned by changing the electric field direction. Therefore, it can be asserted that circular quantum dots or circular rings in the intense THz laser field are equivalent to anisotropic quantum dots or rings respectively, and the electric field direction effectively tunes the single-electron energy spectrum and intraband optical properties of these structures.
关键词： External electric and magnetic fields,Isotropic and unisotropic properties of QDs and QRs,Intraband optical properties of QDs and QRs,Intense THz laser field
更新于2025-09-12 10:27:22
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Dramatic Spectral Broadening of Ultrafast Laser Pulses in Molecular Nitrogen Ions <sup>*</sup>
摘要： We investigate nonlinear interaction of nitrogen molecules with a two-color laser field composed by an intense 800 nm laser pulse and a weak 400 nm laser pulse. It is demonstrated that the spectrum of 400 nm pulses is dramatically broadened when the two beams temporally overlap. In comparison, the spectral broadening in argon is less pronounced, although argon atoms and nitrogen molecules have comparable ionization potentials. We reveal that the dramatic spectral broadening originates from the greatly enhanced nonlinear optical effects in the near-resonant condition of interaction between the 400 nm pulses and the nitrogen molecular ions.
关键词： two-color laser field,spectral broadening,nonlinear interaction,nitrogen molecular ions
更新于2025-09-12 10:27:22
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Coulomb effect on the dynamics of atoms in a strong elliptical laser field: Unification of the excitation and ionization
摘要： We investigate the Coulomb effect on the dynamics of atoms in a strong elliptical laser ?eld by solving the three-dimensional time-dependent Schr?dinger equation with and without the photoelectron core Coulomb interactions and ?nd that the Coulomb effect plays an important role for the excitation and ionization processes, while it is less important for the high-order harmonic generation. Our calculation results can serve as a benchmark for other approximative methods. Looking at the photoelectron momentum distribution, we ?nd that the Coulomb effect is important for the momentum distribution in the polarization plane and less important for the momentum distributions along the normal direction perpendicular to the polarization plane. Similar to the photoabsorption in a weak ?eld, we demonstrate that the excitation and ionization can be treated in a uni?ed way, which implies the low-energy photoelectron distributions can be connected with the populations of highly excited states.
关键词： photoelectron momentum distribution,Coulomb effect,ionization,high-order harmonic generation,excitation,strong elliptical laser field
更新于2025-09-12 10:27:22