Isolated sub-100‐aspulse generation via controlling electron dynamics

Abstract

A new method to coherently control the electron dynamics is proposed using a few-cycle laser pulse in combination with a controlling field. It is shown that this method not only broadens the attosecond pulse bandwidth, but also reduces the chirp, then an isolated 80-as pulse is straightforwardly obtained and even shorter pulse is achievable by increasing the intensity of the controlling field. Such ultrashort pulses allow one to investigate ultrafast electronic processes which have never be achieved before. In addition, the few-cycle synthesized pulse is expected to manipulate a wide range of laser-atom interactions.PACS numbers: 32.80. Qk, 32.80.Wr, 42.65.Re, 42.65.Ky In the past decade, there has been a great interest to extend the pulse duration to the attosecond (as) domain. This is sprung by the great potential of attosecond pulses to trace the electronic dynamics in atoms and molecules [1, 2, 3].The straightforward attosecond metrology prefers an isolated attosecond pulse rather than a train of attosecond pulses [3, 4]. Hence much effort is paid to produce the isolated pulse [3, 4, 5]. It has been shown that an isolated attosecond pulse can be generated with a few-cycle laser pulse by selecting the continuous harmonics in the cutoff [2, 3, 5]. The intractable problem is that the bandwidth of the continuous harmonics in the cutoff is less than 20 eV, and thus the minimum duration of the isolated attosecond pulse is ∼ 250 as [2]. This is greater than the characteristic timescale of the electronic process in atoms (152 as, i.e., the period for electrons in the Bohr orbit of ground-state hydrogens), and then the application of the 250-as pulse is significantly limited. Therefore, it is urgently desired to produce an isolated attosecond pulse with broader bandwidth and shorter duration [6, 7, 8, 9]. It is theoretically demonstrated that broadband continuous harmonics can be produced using a few-cycle laser pulse with a modulated polarization [7]. This scheme has been implemented recently [8, 9], and broadband continuous harmonics are observed. However, there is a chirp in these harmonics, then an isolated 280-as pulse is produced straightforwardly. With the technology of chirp compensation [9], the pulse duration is reduced to 130 as. In this letter, we propose a new facile method for isolated sub-100-attosecond pulse generation via controlling electron dynamics using a few-cycle laser pulse in combination with a controlling field.High harmonic generation (HHG) is well understood in terms of the semiclassical "three-step" model [10]. In detail, the electron is first ionized from the atom, then it oscillates almost freely in the laser field and gains kinetic energy E k , finally, it recombines with the parent ion by releasing an energetic photon of I p + E k where I p is the ionization

Theory of harmonic generation from the hydrogen molecular ion in an inhomogeneous laser field

“…One of them, the HHG is well known due to the fact that it provides a new type of coherence light source of extremely short wavelength that can be widely used in many fields such as attosecond pulse generation [7][8][9][10][11], plasma spectroscopy [12], and X-ray fluorescence analysis [13]. A semiclassical three-step model successfully explains the HHG process [14].…”

Generation of intense isolated attosecond pulses with high spatiotemporal quality by two-color polarization-gating Bessel–Gauss beams

“…Compared with the intensity gating, PG technique allows much broader supercontinuum generation, not only in the cutoff region but also in the plateau region. Previous studies demonstrated that a weak second harmonic (SH) field can be added to modulate the inner dynamics of the HHG process [11] and, even more importantly, to manipulate the ionization step for efficient isolated attosecond burst, which is served as two-color ionization gating [12]. Chang et al combined the two-color field and the PG techniques to simultaneously control ionization and recombination steps, dubbed as double optical gating, and generated an efficient broadband supercontinuum in the plateau [13,14].…”

Generating elliptically polarized isolated attosecond pulses from the 2 p 0 state of He + with a linearly polarized two-color field

“…During the recombination process, a photon with energy equaling to the ionization potential plus the kinetic energy is emitted. Various gating schemes have been proposed to produce isolated attosecond pulses according to the model, such as using a few-cycle laser [5,6], polarization gating [7][8][9][10][11][12], ionization gating [13,14] and two-color or multi-color field [15][16][17][18][19][20][21][22][23][24][25][26], and so on.…”