Fig. 4: HWHM distribution of the transverse momentum.

a Measured and (b) simulated HWHM distribution of transverse electron momentum, whose value reflects the Coulomb focusing effect. The white diamonds, same to those in Fig. 1, denote the measured or simulated MPEAs of photoelectrons for each ATI ring. The white stars represent the simulated streaking angle of the final momentum of the electron emitted at the instant of the electric field peak for each ATI ring