Relativistic ionization rescattering with tailored laser pulses

Abstract

The interaction of relativistically strong tailored laser pulses with an atomic system is considered. Due to a special tailoring of the laser pulse, the suppression of the relativistic drift of the ionized electron and a dramatic enhancement of the rescattering probability is shown to be achievable. The high harmonic generation rate in the relativistic regime is calculated and shown to be increased by several orders of magnitude compared to the case of conventional laser pulses. The energies of the revisiting electron at the atomic core can approach the MeV domain, thus rendering hard x-ray harmonics and nuclear reactions with single atoms feasible.PACS numbers: 42.65. Ky, 32.80.Gc, 32.80.Rm In intense laser-atom interaction phenomena the rescattering concept plays a central role [1]. Here the electron is ionized, propagated in the continuum by the laser field, and finally driven back and scattered at the ionic core in the case of above-threshold ionization (ATI) [2], ionizing further bound electrons in the case of non-sequential double ionization (NSDI) [3], or recombining with the ionic core with high-harmonic generation (HHG) [4]. It is highly desirable to increase the rescattering electron energy [5] as it can be employed to generate higher harmonics [6], to image attosecond dynamics of nuclear processes [7], or to initiate nuclear reactions with a single atom/molecule [8,9]. The electron energy increase can not be achieved by a straightforward increase of the laser intensity. When the laser intensity approaches the relativistic regime, the laser magnetic field effect starts to play a role by inducing a drift of the ionized electron in the laser propagation direction which severely suppresses the probability of the electron revisiting the ionic core. There are several attempts to circumvent this effect in order to increase the efficiency of rescattering, particularly, using relativistic ions which propagate in laser propagation direction [6,8], or using two counter-propagating laser beams with linear [10] or equally handed circular polarization [7], or generating harmonics via exotic positronium atoms in strong laser fields [11]. On a different front, new techniques for generating attosecond pulses have recently emerged based on HHG in gases [12,13] and in plasmas interaction [14,15]. The usage of attosecond pulse trains (APT's) to enhance HHG in a strong laser field has been shown in [16].In this letter we show how efficient recollisions in the relativistic regime are feasible by employing specially tailored strong laser pulses in the form of APT's (see Fig.1).As an indicator of strong field recollision phenomena we consider the HHG process from an ion in a relativistically strong tailored laser pulse (see Fig.2). While in [16] the weak APT serves to solely control the initial conditions of the ionized electron in the strong laser field, we consider By using optimized tailored pulses in the form of an APT instead of conventional sinusoidal pulses it is possible to reduce significantly the drift of the io...

Extremely high-intensity laser interactions with fundamental quantum systems

“…In the weakly relativistic regime the Lorentz force may also be compensated by a second weak laser beam polarized along the direction of propagation of the strong beam (Chirilȃ et al, 2002). Furthermore, the relativistic drift can be significantly reduced by means of special tailoring of the driving laser pulse, which strongly reduces the time when the electron's motion is relativistic with respect to a sinusoidal laser pulse (Klaiber et al, 2006(Klaiber et al, , 2007. Two consecutive laser pulses (Verschl and Keitel, 2007a) or a single laser field assisted by a strong magnetic field can also be used to reverse the drift (Verschl and Keitel, 2007b).…”

Relativistic ionization characteristics of laser-driven hydrogenlike ions

“…The manipulation of the shape of a pulse is a capable tool to control ionization and to generate complex tailored pulses [47]. Besides the peak laser intensities, also the pulse shape of ultrashort and ultrastrong fields is experimentally challenging to measure and, therefore, a crucial parameter to be examined.…”

Enhancing the high-order harmonic generation yield within a specified spectral window via electron wave-packet engineering

“…A cutoff increase by a factor of 3 compared to a sinusoidal pulse with the same period and pulse energy has been attained with the optimally shaped driving pulse. Pulse shaping has also been employed in the relativistic regime of HHG to reduce the effect of the relativistic drift [20,21].…”