Fig. 1. (Color online) (a) Schematic illustration of the overlapping of an IAP (red line) with an IR pulse: time instants t1 and t2 determine the IAP, while t3 and t4 determine the IR pulse. (b) A typical electric field pattern of the overlapped IAP and the IR pulse, for which three categories of circles are defined: the inner circle, the intermediate circles, and the outer circle. IIR=2×1014  W/cm2, IIAP=8×1011  W/cm2.

Fig. 2. (Color online) Electric field patterns of the superimposed IAP and IR pulse in the laser polarization plane for different overlapping parameters. The red curves indicate the superimposed segments. IIR=2×1014  W/cm2, IIAP=2×1011  W/cm2, and θ=θIR=0.

Fig. 3. (Color online) Photoelectron momentum spectra for different overlapping parameters. IIR=2×1014  W/cm2, IIAP=2×1011  W/cm2, θ=θIR=0.

Fig. 4. (Color online) Photoelectron momentum spectra for different initial phases of the IAP: (a) θ=0, (b) θ=π/4, (c) θ=π/2, (d) θ=3π/4, (e) θ=π, (f) θ=5π/4, (g) θ=3π/2, (h) θ=7π/4, and (i) θ=2π. The overlapping parameter η is set to be 0.8. IIR=2×1014  W/cm2, IIAP=2×1011  W/cm2, and θIR=0.

Fig. 5. (a) Rotation angle of the annular photoelectron momentum spectra versus the IAP CEP. (b) Schematic of the rotation angle of the annular photoelectron momentum spectra. The overlapping parameter η is 0.8. IIR=2×1014  W/cm2, IIAP=2×1011  W/cm2, and θIR=0.

Fig. 6. Photoelectron momentum spectra with (a) θIR=0, (b) θIR=π/4, (c) θIR=π/2, (d) θIR=3π/4, (e) θIR=π, (f) θIR=5π/4, (g) θIR=3π/2, (h) θIR=7π/4, and (i) θIR=2π. IIR=2×1014  W/cm2, IIAP=2×1011  W/cm2, η=0.8, and θ=0.

Fig. 7. Photoelectron momentum spectra with (a) θ=1.2π and (b) θ=0.2π. η=0 and θIR=0. IIR=2×1014  W/cm2, and IIAP=2×1011  W/cm2.

Fig. 8. Photoelectron momentum spectra for different overlapping parameters. (a) η=0.92, (b) η=0.88, (c) η=0.84, (d) η=0.8, (e) η=0.76, and (f) η=0.72. IIR=2×1014  W/cm2, IIAP=2×1011  W/cm2, and θ=θIR=0.

Fig. 9. Photoelectron momentum spectra for different initial phases of the IR pulse. (a) θ=0, (b) θ=π/4, (c) θ=π/2, (d) θ=3π/4, (e) θ=π, (f) θ=5π/4, (g) θ=3π/2, (h) θ=7π/4, and (i) θ=2π. η=0.72, IIR=2×1014  W/cm2, IIAP=2×1011  W/cm2, and θIR=0.