Subcycle control of the photoelectron angular distribution using two-color laser fields having different kinds of polarization

We investigate the subcycle control of electron trajectories in single ionization of Ar atoms with two-color laser pulses consisting of a linearly polarized 800-nm field and a circularly polarized 400-nm field. By varying the relative phase between the two fields, the photoelectron angular distribution rotates in the polarization plane and the rotation velocity can be controlled. From the comparison with results obtained with a semiclassical model, we find that the Coulomb field has a greater impact on direct trajectories than on those that undergo a recollision which is opposite to the electron behavior in a monochromatic field. This effect can be directly visualized in the experiment and finely controlled on a subcycle timescale by means of the two-color field scheme. It is shown that the influence of the Coulomb force on the photoelectron momentum distribution is different along the longitudinal and transverse direction.

Figure 1

(a) Illustration of the two-color electric field generated with linearly polarized 800-nm and circularly polarized 400-nm laser pulses in one cycle for $p_{rel}=\pi$. Four colors denote four quarter cycles of the 800-nm laser field. (b) 800-nm (solid red line) and 400-nm (dotted blue line) electric fields along the $z$ direction for $p_{rel}=\pi$. The intensities of the 800- and 400-nm fields are $1.0\times {10}^{14}\mathrm{W}/\mathrm{c}{\mathrm{m}}^2$ and $0.3\times {10}^{14}\mathrm{W}/\mathrm{c}{\mathrm{m}}^2,$ respectively.

Figure 2

(a)–(c) Photoelectron momentum distribution in the $z\text{−}x$ polarization plane for various $p_{rel}$ simulated by the classical trajectory model (a), and CTMC model without (b) and with (c) inclusion of the Coulomb potential. The distribution from π to 2π(0) is central symmetrical of the distribution from 0 to π. The field-driven electron momentum curve $\stackrel{⃑}{p}=-\stackrel{⃑}{A}\left(t_0\right)$ for the specific two-color field is drawn on top of the momentum distributions. The colors encode quarter cycles of the 800-nm field. (d) The PAD with respect to the $p_{rel}$ calculated by the classical trajectory model.

Figure 3

The measured (a) and simulated (b), (c) PADs with respect to the $p_{rel}$. (b), (c) CTMC simulations without (b) and with (c) the parent ion's Coulomb potential included. (d) The measured (open circles) and simulated (solid line) photoelectron emission angle distribution after integrating over the two-color relative phase $p_{rel}$ in the range from 0.5π to 1.5π. The black and red lines represent the results without and with inclusion of the Coulomb potential, respectively.

Figure 4

CTMC simulated PADs as a function of the phase $p_{rel}$ without (a), (c) and with (b), (d) the Coulomb potential for electron trajectories originating from the second (a), (b) and the third (c), (d) quarter cycle of the two-color field, as indicated in the panels. Left panel: Distribution of electron emission angle $\theta$ after integrating over the $p_{rel}$. Right panel: Typical trajectory corresponding to the yield maximum in the distribution. The black and red lines represent the results without and with inclusion of the Coulomb potential, respectively.

Figure 5

The measured (a), (e) and simulated (b), (c), (f), (g) photoelectron momentum distribution for $p_z$ (a)–(c) and $p_x$ (e)–(g) as a function of the $p_{rel}$. (b), (c), (f), (g) CTMC simulations without (b), (f) and with (c), (g) Coulomb potential included. (d), (h) The measured (open circles) and simulated (solid line) photoelectron $p_z$ (d) and $p_x$ (h) distribution after integrating over the $p_{rel}$ in the range from 0.5π to 1.5π [dashed red box in (a)–(c) and (e)–(g)]. The black and red lines represent the results without and with Coulomb potential, respectively. The red arrow indicates the direction of the peak position change from the black line to the red line.

Figure 6

CTMC simulated $p_x$ (a), (b), (d), (e) and $p_z$ (g), (h), (j), (k) distributions as a function of the $p_{rel}$ without (the first column) and with (the second column) Coulomb potential for electron trajectories originating from the second (a), (b), (g), (h) and the third (d), (e), (j), (k) quarter cycle of the two-color field, as indicated in the panels. (c), (f), (i), (l) The corresponding photoelectron $p_x$ (c), (f) and $p_z$ (i), (l) distributions after integrating over the $p_{rel}$ in the range from 0.5π to 1.5π. The black and red lines represent the results without and with Coulomb potential, respectively. The red arrow indicates the direction of the peak position change from the black line to the red line.