Angle-resolved electron spectra in short-pulse two-color XUV$+$IR photoionization of atoms

Spectra and angular distributions of photoelectrons from ionization of atoms by a combination of two short pulses in the XUV and IR range are theoretically considered. The transition from the streaking regime for ultrashort XUV pulses to the sideband formation for longer pulses is discussed. For photoelectrons of sufficiently high energy (a few hundreds of eV), the peculiarity of the angular distribution and the gross structure of the sidebands are investigated.

Figure 1

The calculated electron spectra (thin black lines) excited by the XUV pulses of different durations [(a) 1 fs, (b) 2 fs, (c) 3 fs, (d) 4 fs] in the field of the $3.5\times {10}^{12}$ W/cm${}^2$ IR laser. The duration of the laser pulse is 20 fs. In the inserts the vector potential of the IR and the envelope of the XUV pulses are shown. For further details see text. Thick (red) lines show the averaged spectra. Dashed vertical line shows the position of the unperturbed photoline.

Figure 2

Schematic presentation of the fields and the positions of the stationary phase points $t_s$. Solid (black) line represents a part of the IR vector potential, lines with symbols show envelopes of two XUV pulses. Horizontal dashed line shows the value of $k-\kappa$. For further explanations see the text.

Figure 3

The calculated electron spectra excited by the XUV pulses of durations [(a) 1 fs and (b) 2 fs] for different delay times within one laser period. Solid line $\Delta t=0$, short-dashed line $\Delta t=T_L/8$, dash-dotted line $\Delta t=T_L/4$, dotted line $\Delta t=3T_L/8$, long-dashed line $\Delta t=T_L/2$. In the inset the corresponding lines show the position of the XUV-pulse envelope relative to the IR vector potential. Other parameters of the pulses are the same as in Fig. 1. Dashed vertical line shows the position of the unperturbed photoline.

Figure 4

The calculated energy-angle distributions of photoelectrons for ionization of an $s$ shell for different durations of the XUV pulse (a) 1 fs, (b) 2 fs, and (c) 4 fs. Other parameters are the same as in Fig. 1.

Figure 5

The calculated photoelectron spectra of $s$ subshell photoionization for different detection angles, indicated near the spectra. The XUV pulse duration is 4 fs. Other parameters are the same as in Fig. 1.

Figure 6

The calculated angle-energy distribution of photoelectrons for primary ionization of a $p(\sigma )$ electron into $d(\sigma )$ partial wave. The duration of the XUV pulse is 4 fs, the parameters of the laser pulse are the same as in Fig. 1.

Figure 7

The calculated photoelectron spectra for the primary ionization transition into the $d(\sigma )$ partial wave for different angles of detection, indicated near the spectra. The duration of the XUV pulse is 4 fs, the parameters of the laser pulse are the same as in Fig. 1.