Helicity of harmonic generation and attosecond polarization with bichromatic circularly polarized laser fields*

Abstract

We theoretically investigate the high-order harmonic generation (HHG) of helium atom driven by bichromatic counter-rotating circularly polarized laser fields. By changing the intensity ratio of the two driving laser fields, the spectral chirality of the HHG can be controlled. As the intensity ratio increases, the spectral chirality will change from positive- to negative-value around a large intensity ratio of the two driving fields when the total laser intensity keeps unchanged. However, the sign of the spectral chirality can be changed from positive to negative around a small intensity ratio of the two driving fields when the total laser intensity changes. At this time, we can effectively control the helicity of the harmonic spectrum and the polarization of the resulting attosecond pulses by adjusting the intensity ratio of the two driving laser fields. As the intensity ratio and the total intensity of the driving laser fields increase, the relative intensity of either the left-circularly or right-circularly polarized harmonic can be enhanced. The attosecond pulses can evolve from being elliptical to near linear correspondingly.

Ultrafast photoionization of ions and molecules by orthogonally polarized intense laser pulses: Effects of the time delay*

“…The strong-field physics is a hot topic in recent years, and interaction of laser with atoms or molecules can produce different physical phenomena, including high order harmonic generation (HHG), [1][2][3] strong-field ionization, and nonsequential double ionization (NSDI). [4] The electron processes of molecular reaction dynamics are investigated with the rapid advances of ultrashort and ultrafast intense laser technology [5][6][7] in the attosecond time regime (1 as = 10 −18 s) and sub-nanometer dimensions.…”

Effects of initial electronic state on vortex patterns in counter-rotating circularly polarized attosecond pulses*

“…[5] The ultrashort attosecond pulses can also induce electron charge migration, thus offering the possibility for probing the molecular structure and imaging the molecular reactions. [6][7][8] In the research, a variety of pulses and their combinations have been used to explore electron dynamics, including the high-order harmonic generation (HHG), [9][10][11][12][13][14] nonsequential double ionization (NSDI), [15][16][17][18] and the photoelectron momentum distribution (PMD). [19][20][21][22][23] Recently it was found that single ionization of atom by two oppositely circularly polarized, time-delayed attosecond pulses produce vortex patterns in PMDs, [24][25][26][27] which are sensitive to the time delay between the pulses, their handedness, and their relative phase.…”

Role of potential on high-order harmonic generation from atoms irradiated by bichromatic counter-rotating circularly polarized laser fields*

“…When an atom is irradiated by such an intense ultrashort laser pulse, the ultra-wide-band (from ultraviolet to x-ray) coherent high-order harmonic generation (HHG) can be carried out. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] HHG has been applied in the attosecond science [19][20][21] and nonlinear optics in the XUV region. [22] The harmonic spectrum from atoms in the linearly polarized laser pulse presents typical characteristics: as the harmonic order increases, the intensity of the first few order harmonics drops rapidly, and then a so-called "plateau" appears, the harmonic intensity which changes little, and there is a cut-off (beyond this energy the harmonic intensity decreases rapidly) at the end of the plateau.…”