Author Affiliations
^{1}Huazhong University of Science and Technology, School of Physics and Wuhan National Laboratory for Optoelectronics, Wuhan, China^{2}Wuhan Institute of Technology, Hubei Key Laboratory of Optical Information and Pattern Recognition, Wuhan, Chinashow less

Fig. 1. (a)–(c) The experimentally measured PEMDs for strong-field tunneling ionization of Ar by the parallel two-color ($800\text{\hspace{0.17em}\hspace{0.17em}}\mathrm{nm}+400\text{\hspace{0.17em}\hspace{0.17em}}\mathrm{nm}$) field with relative phase $\phi =0$, $0.5\pi $, and $1.5\pi $, respectively. The laser intensities of the FM and SH fields are $1.2\times {10}^{14}$ and $0.3\times {10}^{11}\text{\hspace{0.17em}\hspace{0.17em}}\mathrm{W}/{\mathrm{cm}}^{2}$, respectively. (d)–(f) NDs for the distributions in (a)–(c) (see text for details).

Fig. 2. (a) The ND as a function of $\phi $ for the momentum $({p}_{x},{p}_{y})=(-0.6,0.1)$ a.u. The open circles show the experimental data and the green curve shows the fitted results. (b) The fitted ND by Eq. (2) as a function of $\phi $ for the momentum $({p}_{x},{p}_{y})=(-0.6,0)$ (blue curve), $(-0.6,0.1)$ (purple curve), and $(-0.6,0.2)$ a.u. (green curve). The data are normalized such that the maximum of each curve is unity. (c) Same as (b) but for $({p}_{x},{p}_{y})=(-0.4,0)$ (black curve), $(-0.5,0)$ (red curve), and $(-0.6,0)$ a.u. (yellow curve). (d) The optimal phase ${\phi}_{m}$ in the region of ${p}_{x}\in [-1.1,1.1]$ a.u. and ${p}_{y}\in [-0.5,0.5]$ a.u. (e) Cuts of ${\phi}_{m}$ at ${p}_{x}=-0.4$ a.u. (red crosses), $-0.5$ a.u. (green squares), and $-0.6$ a.u. (blue triangles). The error bars show the 95% confidence interval in fitting.

Fig. 3. (a) Illustration of the ionization times of the long and short orbits in strong-field tunneling ionization. The long and short orbits correspond to the ionization events, where the electron is released at the falling and rising edges of electric field, respectively. The blue curve indicates the electric field of the FM field and the red curve shows its vector potential. (b) The $\mathrm{ND}(\mathbf{p};\phi )$ for the long orbit with transverse momentum ${p}_{y}=0$, calculated by CCSFA. The solid red curve indicates the optimal phase ${\phi}_{m}^{\mathrm{L}}$. (c) The same as (b) but for the short orbit. The black arrow denotes the phase window formed by ${\phi}_{m}^{\mathrm{L}}$ and ${\phi}_{m}^{\mathrm{S}}$. (d) The optimal phase ${\phi}_{m}^{\mathrm{L}}$ of the long orbit for ${p}_{x}\in [-1,-0.2]$ a.u. and ${p}_{y}\in [-0.36,0.36]$ a.u. (e) The same as (d) but for the short orbit.

Fig. 4. (a) The ND at $({p}_{x},{p}_{y})=(-0.5,0)$ a.u. as a function of $\phi $. The solid green and purple curves show the theoretical results of the signal from the long and short orbits, respectively. The black squares represent the experimental data, where both the long and short orbits contribute. The dashed blue lines indicate the optimal phases ${\phi}_{m}^{\mathrm{L}}$ and ${\phi}_{m}^{\mathrm{S}}$, and the blue arrow denotes their phase window. (b) The same as (a) but for $({p}_{x},{p}_{y})=(-0.5,0.2)$ a.u. (c) The ratios $\alpha /\beta $ extracted from the experimental data. (d) The cuts of $\alpha /\beta $ at ${p}_{x}=-0.4$ (red circles), $-0.6$ (green squares), and $-0.95$ a.u. (purple triangles), respectively.