Attosecond near-threshold photoionization in a strong laser field

A drastic modification of the conventional streaking patterns of double differential cross section for attosecond near-threshold ionization of atoms in a strong infrared (IR) field is theoretically investigated. Rescattering of slow electrons from the ionic core leads to appearance of the interference fringes and strong diffraction maxima in the spectra of photoelectrons at small energies. The computations based on solving the time-dependent Schrödinger equation show that both these spectral features strongly depend on the IR intensity and frequency. Investigations of low-energy streaking can provide unique information on slow photoelectron dynamics in combined fields of ionic core and strong IR laser.

Figure 1

IR electric field (solid red line) and the envelopes of the XUV pulses (solid black lines) in arbitrary units at different time delays, discussed in the text. Line “a” corresponds to $t_{\mathrm{delay}}=3.60$ fs, line “b” corresponds to $t_{\mathrm{delay}}=4.34$ fs, and line “c” corresponds to $t_{\mathrm{delay}}=5.0$ fs. Dashed line shows vector potential of the IR field.

Figure 2

A two-dimensional (2D) plot of the DDCS for Ne(2s) photoionization at the time delay between XUV and IR pulses 3.60 fs for four values of the excess energy (a) 12.4 eV, (b) 7.4 eV, (c) 0.4 eV, and (d) $-0.6$ eV.

Figure 3

Spectra of electrons emitted in forward direction (left column) and backward direction (right column) for different excess energy: 1: 12.4 eV; 2: 7.4 eV; 3: 5.4 eV; 4: 2.4 eV; 5: 0.4 eV. Time delay is 3.6 fs (upper row) and 5.0 fs (lower row). For these delays the vector potential of the IR field is close to zero.

Figure 4

The same as in Fig. 2 but for the time delay 4.34 fs, corresponding to the maximum of the IR vector potential.

Figure 5

Spectra of electrons emitted in forward direction (left panel) and backward direction (right panel) for different excess energy: 1: 7.4 eV; 2: 5.4 eV; 3: 2.4 eV; 4: 0.4 eV. Time delay is 4.34 fs, corresponding to the maximum of the IR vector potential.

Figure 6

A 2D color-scale plot of $\text{ln}\left|\psi \right(\vec{r},T_{\max }\left)\right|$ at $T_{\max }=12.4$ fs for Ne(2s) photoionization as a function of coordinates $z$ and $x$ at the time delay between XUV and IR pulses $t_{\mathrm{delay}}=3.6\mathrm{fs}$ and $E_{\mathrm{ex}}=0.4$ eV (upper panel), and $t_{\mathrm{delay}}=4.34\mathrm{fs}$ and $E_{\mathrm{ex}}=7.4\mathrm{eV}$ (lower panel). The IR field is polarized along the $z$ axis and the wave packet is axially symmetrical.

Figure 7

Spectra of photoelectrons emitted in forward (a) and backward (b) directions for ${\omega }_L=1.55\mathrm{eV}$ and different IR intensities: 1: 0.56; 2: 1.0; 3: 2.5; and 4: 5.6 in units ${10}^{13}{\mathrm{W}/\mathrm{cm}}^2$. Excess energy is $E_{\mathrm{ex}}=2.4\mathrm{eV}$.

Figure 8

Spectra of photoelectrons emitted in forward (a) and backward (b) directions for IR intensity $5.6\times {10}^{12}{\mathrm{W}/\mathrm{cm}}^2$ and different IR frequencies: 1: 0.83 eV; 2: 1.16 eV; and 3: 1.55 eV. Excess energy is $E_{\mathrm{ex}}=2.4\mathrm{eV}$.