High-order harmonic generation from ${\mathrm{H}}_{2}{}^{+}$ irradiated by a co-rotating two-color circularly polarized laser field

High-order harmonic generation from $H_{2}^{+}$ irradiated by a co-rotating two-color circularly polarized laser field

Yue Qiao, Dan Wu, Ji-Gen Chen, Jun Wang, Fu-Ming Guo, and Yu-Jun Yang

Phys. Rev. A 100, 063428 – Published 30 December 2019

Abstract

The high-order harmonic generation process of $H_{2}^{+}$ in a co-rotating two-color circularly polarized laser pulse was investigated by numerically solving the time-dependent Schrödinger equation. Compared with the target of the atom, the harmonic intensity of $H_{2}^{+}$ is remarkably enhanced. Moreover, the harmonic intensity of $H_{2}^{+}$ approaches its maximum when the electric field amplitude ratio of the fundamental frequency and the second one is approximately 1:2.3. By analyzing the evolution of the time-dependent wave packets, the enhancement of harmonic intensity may be attributed to an increase in the probability of the ionized electron recolliding with the parent ion. In addition, the dependence of harmonic intensity on the internuclear distance and the alignment angle of $H_{2}^{+}$ is explored. We found that the ellipticity of the particular harmonic order changes with the molecular alignment angle, which provides a chance to generate an extreme ultraviolet coherent light pulse with controllable polarization.

Received 31 May 2019
Revised 9 December 2019

DOI:https://doi.org/10.1103/PhysRevA.100.063428

Physics Subject Headings (PhySH)

High-order harmonic generation

Atomic, Molecular & Optical

Authors & Affiliations

Yue Qiao^1,2, Dan Wu^1,2, Ji-Gen Chen³, Jun Wang^1,2,*, Fu-Ming Guo^1,2,†, and Yu-Jun Yang ^1,2,‡

¹Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China
²Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy (Jilin University), Changchun 130012, China
³Department of Materials Engineering, Taizhou University, Taizhou 318000, China

^*wangjun86@jlu.edu.cn
^†guofm@jlu.edu.cn
^‡yangyj@jlu.edu.cn

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Vol. 100, Iss. 6 — December 2019

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Figure 1
Comparison of harmonics generated by $H_{2}^{+}$ and the atom under different forms of driving lasers. (a) Harmonic spectra of $H_{2}^{+}$ and the atom by the co-rotating two-color circularly polarized laser. The inset shows the electric fields of the CRTCCP laser when the amplitude ratios are 1:2.3 (solid red line) and 1:1 (dashed black line), and the counterclockwise rotation direction of the two fields is marked with red and black arrows, respectively. The angle between the molecular axis and the $x$ axis is also depicted here. (b) The harmonic spectra of $H_{2}^{+}$ by the co-rotating (solid red line) and counter-rotating (dash-dotted black line) two-color circularly polarized lasers. (c) The harmonic spectra of $H_{2}^{+}$ by the co-rotating two-color circularly polarized field using an 800–400-nm laser pulse (solid red line) and linearly polarized 800-nm (dashed black line) and 400-nm (dash-dotted blue line) lasers. (d) The harmonic spectra of $H_{2}^{+}$ by the co-rotating two-color circularly polarized field using an 800–400-nm laser pulse (solid red line) and circularly polarized 800-nm (dashed black line) and 400-nm (dash-dotted blue line) lasers.
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Figure 2
The wave-packet motion of (a)–(d) the atom and (e)–(h) $H_{2}^{+}$ at different times $T_{a}, T_{b}, T_{c}$ , and $T_{d}$ in the co-rotating two-color circularly polarized laser. The arrow indicates that the electron probability flow and the solid black lines in (e)–(h) all represent the classic electronic trajectory of the $T_{a} - T_{d}$ period, where the purple dot indicates the electronic position at the corresponding time, and the electric fields of the corresponding four moments are shown as the red dot in the solid black line of (d).
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Figure 3
(a) HHG of $H_{2}^{+}$ in the CRTCCP laser pulse with different amplitude ratios. (b) The 26th (black square) and 29th (blue circle) harmonic intensity, and the recollision probability (red triangle) as a function of the amplitude ratio.
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Figure 4
(a)–(d) The instantaneous variations of the electric field vector with different amplitude ratios; (e)–(h) classical motion trajectories in different ionization instants at one optical cycle for different amplitude ratios.
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Figure 5
(a) The harmonic spectrum comparison of $H_{2}^{+}$ at $R = 2$ (black line) and $R = 3.2$ (red line) in the co-rotating two-color circular polarization field. (b) The intensity comparison of the 20th-order (black square) and 21st-order (red circle) harmonics of $H_{2}^{+}$ in the co-rotating two-color circular polarization field at different internuclear distance, and the ionization probability as a function of the internuclear distance (five-pointed purple star). $H_{2}^{+}$ in the counter-rotating two-color circular polarization field of the 20th-order (blue triangle) and monochromatic linear polarization field of the 21st-order (red circle) harmonic intensity as a function of the internuclear distance.
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Figure 6
(a) Ionization yield, (b) harmonic intensity in the plateau region, (c) 23rd harmonic ellipticity, and (d) harmonic ellipticity in the plateau as a function of the angle.
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Physical Review A

covering atomic, molecular, and optical physics and quantum information

High-order harmonic generation from $H_{2}^{+}$ irradiated by a co-rotating two-color circularly polarized laser field

Yue Qiao, Dan Wu, Ji-Gen Chen, Jun Wang, Fu-Ming Guo, and Yu-Jun Yang

Phys. Rev. A 100, 063428 – Published 30 December 2019

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Physical Review A

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High-order harmonic generation from H2+ irradiated by a co-rotating two-color circularly polarized laser field

Yue Qiao, Dan Wu, Ji-Gen Chen, Jun Wang, Fu-Ming Guo, and Yu-Jun Yang

Phys. Rev. A 100, 063428 – Published 30 December 2019

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High-order harmonic generation from $H_{2}^{+}$ irradiated by a co-rotating two-color circularly polarized laser field