Attosecond x-ray sources generation from pre-excited He⁺ions using mid-infrared homogeneous and inhomogeneous fields

Abstract

A promising method is proposed to generate the intense ultrabroadband supercontinuum spectra and the ultrashort attosecond x-ray pulses from pre-excited He + ion with the homogeneous and inhomogeneous two-color mid-infrared laser field combined with a unipolar pulse. For the homogeneous case, by optimizing the two mid-infrared pulses and the unipolar pulse, not only the harmonic cutoff has been extended, but also the harmonic modulation has been remarkably reduced. Moreover, we found the above harmonic extension scheme can be achieved in the multi-cycle pulse region and by preparing the initial state of He + ion as the coherent superposition of the ground and the first excited states, the harmonic yield can be enhanced by 4-6 orders of magnitude compared with the case of the single ground initial state. Furthermore, with the introduction of the inhomogeneous of the combined field, the harmonic cutoff can be further enhanced, resulting in a supercontinuum with the bandwidth of 1648 eV. As a result, a series of intense 32as x-ray pulses can be obtained, which are 4-6 orders of magnitude improvement in comparison with the single initial state case.

Half-cycle waveform control for producing a broad and intense harmonic spectral continuum and an isolated attosecond pulse

“…Thus, there are also many reports on the control of the ionization process. For instance, in atomic systems, use of the ultraviolet (UV) resonance ionization scheme [20,21], superposition of the initial states [22,23] and the high Rydberg initial state [24,25], can enhance the harmonic yield. In H 2 + and its isotopic molecule systems, the charge resonance enhanced ionization scheme is an effective method for improving the harmonic intensity [26][27][28].…”

“…As can be seen, if one wants to obtain a broad and intense harmonic spectral region, proper control of the ionization and acceleration processes is necessary. However, in previous investigations [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28], control of the ionization and acceleration processes of the free electron has always been discussed separately. Thus, in this paper, the harmonic emission process in the half-cycle waveform has been well controlled by proper choice of the half-cycle waveform.…”

Polarization property of high harmonics generated from nitrogen molecule by bichromatic counter-rotating circularly polarized laser fields

“…Many properties about HHG have been reported and studied for atom targets. By using the synthesized mid-infrared inhomogeneous field interacted with pre-excited He + ion, the harmonic cutoff has been extended and a series of intense 32as x-ray pulses has been obtained [11]. The HHG from a twodimensional model of an Ar + cluster in a synthesized twocolor laser pulse has been investigated, a continuous spectrum with a bandwidth of 100 eV and an isolated attosecond with a duration of about 45as have been generated [12].…”

Waveform control in selective enhancement of single-order harmonic

“…Thus, on the basis of the TSM, lots of schemes have been proposed to achieve the above requirements For instance, in the case of harmonic cutoff extension, by properly using the multi-color combined field [11][12][13][14][15][16][17]; the polarization gating technology [18][19][20][21][22]; the frequency-chirping technology [23][24][25] and the plasmonic field enhancement field [26][27][28][29][30], many ultrashort SAPs in XUV and x-ray regions can be produced. In the case of harmonic yield enhancement, the uses of excited initial state or superposition of initial state in atomic system [31][32][33]; and the uses of vibrational excited initial state or charge resonance enhanced ionization scheme in H + 2 molecule ion [34][35][36], the intensities of HHG yield and the produced SAPs can be enhanced by several orders of magnitudes.…”