Conditions for perfect circular polarization of high-order harmonics driven by bichromatic counter-rotating laser fields
- National Taiwan Univ., Taipei (Taiwan). Center for Quantum Science and Engineering, and Center for Advanced Study in Theoretical Sciences, Dept. of Physics
- St. Petersburg State Univ., St. Petersburg (Russia). Dept. of Physics
- National Taiwan Univ., Taipei (Taiwan). Center for Quantum Science and Engineering, and Center for Advanced Study in Theoretical Sciences, Dept. of Physics; Univ. of Kansas, Lawrence, KS (United States). Dept. of Chemistry
Recently, studies of high-order harmonic generation (HHG) from atoms driven by bichromatic counter- rotating circularly polarized laser fields have received considerable attention for this process could be a potential source of coherent circularly polarized extreme ultraviolet (XUV) and soft-x-ray beams in a tabletop-scale setup. In this paper, we address the problem with molecular targets and perform a detailed quantum study of the H2+ molecule in bichromatic (ω0, 2ω0) counter-rotating circular polarized laser fields where we adopt wavelengths (790 and 395 nm) and intensities (2×1014 W/cm2) reported in a recent experiment [K. M. Dorney et al., Phys. Rev. Lett. 119, 063201 (2017)]. Here, we demonstrate appropriate conditions to produce perfectly circular polarized harmonics. The calculated radiation spectrum contains doublets of left and right circularly polarized harmonics which display perfect circular polarization with use of the trapezoidal pulse shape, and substantial deviations from perfect circular polarization with use of the sine-squared pulse shape. We also study in detail short- and long-cycle counter-rotating circularly polarized driving pulses with a time delay between the two driving fields, ω0 and 2ω0. These time delayed circularly polarized driving pulses are applied to H atoms and H2+ molecules, and in both atomic and molecular cases we conclude a zero time delay corresponds to the highest HHG intensity for short pulses. Finally, for longer pulses there are no distinct differences in HHG intensities between the zero and nonzero time delays if the latter are within a few optical cycles of the fundamental frequency.
- Research Organization:
- Univ. of Kansas, Lawrence, KS (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES); Ministry of Science and Technology of Taiwan; National Taiwan University
- Grant/Contract Number:
- FG02-04ER15504; 106R104021; 106R891701
- OSTI ID:
- 1494913
- Journal Information:
- Physical Review A, Vol. 99, Issue 2; ISSN 2469-9926
- Publisher:
- American Physical Society (APS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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