Effect of multiple rescatterings on continuum harmonics from asymmetric molecules in multicycle lasers

Abstract

A wide range of harmonics especially continuum harmonics is a prerequisite for attosecond pulses generation. One can use longer-wavelength lasers to push the cutoff to a higher order. However, this...

Regulation of Continuum Harmonic Generation by Using Near-infrared Chirped Pulses

“…The results show that except for β c = 12 with the twin pulse, the generated pulses are a single pulse whose bandwidth and intensity are respectively shorter and higher with larger harmonic range. It has been known that in multicycle lasers, a train of twin pulses is generated from the long and short electron trajectories, while a train of single pulses indicates only one kind of electron trajectory existing [8]. Especially, these results show that the single attosecond pulse, usually achieved by few-cycle lasers, can be produced with multicycle pulses when using the chirping technique.…”

“…The second fact is the different cutoffs for the two opposite orientations. This distinction originates from the asymmetry nature of the polar molecules and the symmetry-breaking of the temporal profile of chirped pulse [8]. Indeed, at orientation θ = 0˚, the bursts around the odd points: R 3 (t r = 3.2T 0 ), R 5 (t r = 4.2T 0 ), R 7 (t r = 5.2T 0 ) predominate, while at orientation θ = 180˚, the bursts around even points R 2 (t r = 2.65T 0 ), R 4 (t r = 3.7T 0 ), R 6 (t r = 4.7T 0 ) take over as shown in the SST spectra in Fig.…”

“…The Schrödinger equation is then for one electron only. Its construction and the solving method were given in detail in our previous studies [8,15]; therefore, we present here only the main points of the method.…”

“…However, when using such a longer wavelength laser, the electron can reencounter many times before recombination, creating the sophisticated process due to the arising contribution of high-order rescatterings (HOR) into the harmonic spectrum [5][6][7]. In principle, to optimize the range of continuum harmonics whose benefit is producing attosecond pulse trains (APT), we should remove the contribution of HOR [6,8].…”

“…Thanks to the development of laser technology, to fulfill the mentioned-above issues, we can either add an extra field, such as static [9] or vacuum ultraviolet (VUV) [6,10], or use a specific laser with the frequency changing in time, i.e., the chirping form used in Ref. [11] as we figured out in our previous work [8]. In that study, we presented a specific case of an up-chirped laser with the frequencies increasing with time to demonstrate the possibility of controlling the HOR.…”