Within a semiclassical description of above-threshold ionization (ATI) we identify the interplay between intracycle and intercycle interferences. The former is imprinted as a modulation envelope on the discrete multiphoton peaks formed by the latter. This allows one to unravel the complex interference pattern observed for the full solution of the time-dependent Schrödinger equation (TDSE) in terms of diffraction at a grating in the time domain. These modulations can be clearly seen in the dependence of the ATI spectra on the laser wavelength. Shifts in energy modulation result from the effect of the long Coulomb tail of the atomic potential.Tunneling ionization is a highly nonlinear quantummechanical phenomenon induced by intense laser pulses (> ∼ 10 14 W/cm 2 ). Electrons are emitted by tunneling through the potential barrier formed by the combination of the atomic potential and the external strong field. Tunneling has recently attracted increasing interest as a probe of the atomic and molecular structure [1-3]. Tunneling occurs within each optical cycle predominantly around the maxima of the absolute value of the electric field. The interference of the successive bursts of ejected electrons reaching the same final momentum gives rise to features in photoelectron energy and momentum distribution which are markedly different from typical above-threshold ionization (ATI) spectra by multicycle lasers. This temporal double-slit interference has recently been studied both experimentally [1,4] and theoretically [5]. On the other hand, the ATI peaks separated by a photon energy can be themselves viewed as an interference pattern formed by electron bursts repeated each optical cycle. Details of the interplay between these intra-and intercycle interferences have not yet been clearly identified and analyzed, to the best of our knowledge.In this Rapid Communication, we study the influence of different interference processes on ATI spectra generated by multicycle laser pulses. We clarify the underlying mechanism within a simple one-dimensional (1D) model employing classical trajectories. Within the framework of the strongfield approximation (SFA) [6] the qualitative features, the modulation of the ATI peaks akin to the modulation of Bragg peaks by the structure factor in crystal diffraction, can be unambiguously identified in the ATI spectrum determined from the full solution of the three-dimensional time-dependent Schrödinger equation (TDSE). The multicycle laser pulse thus acts as a diffraction grating in the time domain. Quantitative deviations between the SFA predictions and the full TDSE can be traced to the Coulomb tail of the atomic potential affecting this modulation. The latter opens up the opportunity to observe effects of the atomic potential in easy-to-obtain photoelectron spectra after ionization by multicycle laser pulses.Our simple semiclassical model of photoelectron spectra is based on the 1D "simple man's model (SMM)" [6][7][8]. Let us consider an atom interacting with a linearly polarized laser pulse. The...

We investigate the dependence of the intensity of radiation due to high-harmonic generation as a function of the wavelength lambda of the fundamental driver field. Superimposed on a smooth power-law dependence observed previously, we find surprisingly strong and rapid fluctuations on a fine lambda scale. We identify the origin of these fluctuations in terms of quantum path interferences with up to five returning orbits significantly contributing.

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We analyze the photoelectron emission spectrum in atomic above-threshold ionization by a linearly polarized short-laser pulse. Direct electrons can be characterized by both intracycle and intercycle interferences. The former results from the coherent superposition of two different electron trajectories released in the same optical cycle, whereas the latter is the consequence of the superposition of multiple trajectories released in different cycles. In the present article, a semiclassical analytical expression for the complete (both intracycle and intercycle) interference pattern is derived. We show that the recently proposed semiclassical description in terms of a diffraction process at a time grating remains qualitatively unchanged in the presence of the long-range Coulomb potential. The latter causes only a phase shift of the intracycle interference pattern. We verify the predictions of the semiclassical model by comparison with full three-dimensional (3D) time-dependent Schrödinger equation (TDSE) solutions.One key finding is that the subcycle interference structures originating from trajectories launched within a time interval of less than 1 femtosecond should be experimentally observable also in low-resolution spectra for longer multicycle pulses.

Recent experiments have demonstrated that highly charged ions can be guided through insulating nanocapillaries along the direction of the capillary axis for a surprisingly wide range of injection angles. Even more surprisingly, the transmitted particles remain predominantly in their initial charge state, thus opening the pathway to the construction of novel ion-optical elements without electric feedthroughs. We present a theoretical treatment of this self-organized guiding process.We develop a classical trajectory transport theory that relates the microscopic charge-up with macroscopic material properties. Transmission coefficients, angular spread of transmitted particles, and discharge characteristics of the target are investigated. Partial agreement with experiment is found.