Figure 1

(a) Schematic trajectory of the tunneled electron in circularly polarized light. The drift momentum of the electrons in the plane of laser polarization, summed over possible angles of the ionization field, yields a toroidal distribution of momentum where the center of the ring is $E/{\omega }_L$. The thickness of this distribution perpendicular to the laser polarization is the width of the momentum distribution at ionization. (b) Measured momentum spectrum of Ar photo electron in circularly polarized light at an intensity of $3.1\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$, 800 nm. The laser propagates along the $z$ axis. The integrated profile along the direction of propagation (top) is in good agreement with a Gaussian distribution. The integrated profile in the plane of polarization (side) is used to determine the intensity.Reuse & Permissions

Figure 2

(a) Measured and calculated distributions at $3.2\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$, integrated along the propagation axis. The quality of the fit to data is significantly improved by including the momentum distribution of tunneled electrons in our algorithm. (b) The electron wave packet at 800 and 1400 nm is shown along the $p_z$ axis. The laser intensity was $1.8\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$ for both wavelengths. Also shown is a Gaussian fit to the measurement and the prediction of the ADK theory [Eq. (2)] at this intensity. The small offset of the center from zero is due to photon linear momentum [33].Reuse & Permissions

Figure 3

(a) Width $\sigma$ of the momentum distribution as a function of average laser field in the focus for argon at 800 and 1400 nm. The data are compared with predictions of nonadiabatic and ADK theories. (b) Width of the momentum distribution as a function of the field for neon.Reuse & Permissions

Figure 4

Integrated lateral distribution from ionization of Ar at 400 nm using circularly polarized light at approximately $2\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$. Inset shows the measured 2D electron distribution (log color scale).Reuse & Permissions