Fig. 1. (a) TEDs of electrons along the positive x axis (Θ = 0) emitted by two XUV pulses (φ_XUV = 0) separated by a half-cycle of an 800 nm IR field. Panels (b) and (c) show the ITDs of electrons obtained by integrating the TED over the energy for φ_XUV = 0 and φ_XUV = 0.5π, respectively. The corresponding electric fields of the two XUV pulses are also given (gray dashed dotted line).

Fig. 2. Frequency spectrum of the double-XUV pulse with parameters like those of Fig. 1(a).

Fig. 3. Electric fields of two XUV pulses with φ_XUV = 0 (gray solid line) and an 800 nm IR (red solid line) pulse. (a) Case one: the center of the XUV pulse coincides with the zero crossings of the IR field amplitude. (b) Case two: the center of the XUV pulse coincides with the maximum of the IR field amplitude. The blue dashed lines represent the sum of the two XUV and IR fields, and the black dashed lines denote the negative vector potential of the IR field. Magenta (green) dotted lines denote the electric field of the XUV pulse that is enhanced (suppressed) after adding the IR field. Here, I_IR = 1 × 10¹³ W/cm².

Fig. 4. TEDs of electrons emitted along the positive (left column) and negative (right column) directions in the two-color field of case one. The intensities of the IR field are (a), (b) 1 × 10¹¹ W/cm², (c), (d) 1 × 10¹² W/cm², and (e), (f) 1 × 10¹³ W/cm², respectively. The white solid line denotes the energy spectrum.

Fig. 5. TEDs of electrons emitted along the positive (left column) and negative (right column) directions in the two-color field of case two. The intensities of the IR field are (a), (b) 1 × 10¹¹ W/cm², (c), (d) 1 × 10¹² W/cm²), and (e), (f) 1 × 10¹³ W/cm², respectively. The white solid lines denote the energy spectra.

Fig. 6. ITDs of the photoelectron emitted along the positive (left column) and negative (right column) directions for the two-color fields of (a), (b) case one and (c), (d) case two. The peak of the ITD is enlarged in the inset.

Fig. 7. TEDs of the photoelectron generated from an atom with I_P = 1.3 a.u. by two XUV pulses in the presence of a 1600 nm IR field with I_IR = 1 × 10¹³ W/cm² in the (a) positive and (b) negative directions. The two-color field is the same as case one shown in Fig. 3(a), except for the IR wavelength of 1600 nm. Solid lines denote the energy spectra, and the dashed lines represent the ITDs.