Multistart spiral electron vortices in ionization by circularly polarized UV pulses

Abstract

Multistart spiral vortex patterns are predicted for the electron momentum distributions in the polarization plane following ionization of the helium atom by two time-delayed circularly polarized ultrashort laser pulses. For two ultraviolet (UV) pulses having the same frequency (such that two photons are required for ionization), single-color two-photon interferometry with corotating or counter-rotating time-delayed pulses is found to lead respectively to zero-start or four-start spiral vortex patterns in the ionized electron momentum distributions in the polarization plane. In contrast, two-color one-photon plus two-photon interferometry with time-delayed corotating or counter-rotating UV pulses is found to lead respectively to one-start or three-start spiral vortex patterns. These predicted multistart electron vortex patterns are found to be sensitive to the carrier frequencies, handedness, time delay, and relative phase of the two pulses. Our numerical predictions are obtained by solving the six-dimensional two-electron time-dependent Schrödinger equation (TDSE). They are explained analytically using perturbation theory (PT). Comparison of our TDSE and PT results for single-color two-photon processes probes the role played by the time-delay-dependent ionization cross channels in which one photon is absorbed from each pulse. Control of these cross channels by means of the parameters of the fields and the ionized electron detection geometries is discussed.

Kinematical vortices in double photoionization of helium by attosecond pulses

“…Our predictions stem from kinematic factors and are thus applicable to singleionization processes for any target system, as demonstrated recently by Yuan et al [47] for odd-start electron vortices in two-color single ionization of the H + 2 molecule. Very recently, our predicted spiral electron vortices [44,45] were experimentally observed in multiphoton single ionization of potassium atoms by a pair of time-delayed oppositely circularly polarized fs pulses [48]. For two-color, circularly polarized pulses having zero time delay, our predictions [45] are consistent with results for two-color single ionization of Ar [49] and H [50] atoms.…”

“…Intriguing electron phenomena were predicted in photoionized electron momentum distributions, including two-start spiral electron vortices in single-electron photoionization by a pair of oppositely circularly polarized attosecond xuv pulses [44] and multistart spiral electron vortices in single-electron multiphoton ionization by two circularly polarized uv pulses [45]. These matter wave spiral patterns require the broad bandwidth characteristic of ultrashort pulses and stem from an unusual kind of Ramsey interference of the single-electron wave packets produced by each of the time-delayed, oppositely circularly polarized pulses.…”

“…Recently, we have developed ab initio analytical and numerical tools for treating the He atom exposed to two time-delayed ultrashort circularly polarized pulses [44,45]. Intriguing electron phenomena were predicted in photoionized electron momentum distributions, including two-start spiral electron vortices in single-electron photoionization by a pair of oppositely circularly polarized attosecond xuv pulses [44] and multistart spiral electron vortices in single-electron multiphoton ionization by two circularly polarized uv pulses [45].…”

“…These matter wave spiral patterns require the broad bandwidth characteristic of ultrashort pulses and stem from an unusual kind of Ramsey interference of the single-electron wave packets produced by each of the time-delayed, oppositely circularly polarized pulses. Moreover, the even-start electron matter-wave vortices from single ionization [44,45] were found to have a counterpart in optics [46], providing thus a dramatic example of wave-particle duality. Our predictions stem from kinematic factors and are thus applicable to singleionization processes for any target system, as demonstrated recently by Yuan et al [47] for odd-start electron vortices in two-color single ionization of the H + 2 molecule.…”

Ultrashort polarization-tailored bichromatic fields from a CEP-stable white light supercontinuum

“…Ultrashort bichromatic laser fields have emerged as a new twist to coherently control ultrafast electron dynamics in atoms [1][2][3][4][5][6], molecules [7][8][9] and solids [10][11][12]. In recent years, (ω : 2ω)-fields have been employed in numerous applications to observe and manipulate the motion of electron wave packets on their intrinsic timescales.…”