Ouroboros-like electron spirals from photoionization by synchronous crossed chirped laser pulses

Even-arm spiral patterns in the photoelectron momentum distribution (PMD) by photoionization of an S-state atom using time-delayed co-propagating oppositely circularly polarized attosecond transform-limited pulses (TLPs) was predicted$^{1}$ in 2015, and confirmed experimentally$^{2}$ in 2017. In 2021, time-delayed crossed TLPs involving linear and circular polarizations were shown to lead to single-arm spiral patterns$^{3}$. However, a reliable time delay is feasible but hard to attain with crossed pulses in an experimental setting. The 2022 discovery of reversible spiral patterns$^{4}$ by co-propagating synchronous laser pulses that are chirped (instead of having a time delay) suggests that new patterns can emerge when revisiting the 2021 scheme using chirped pulses. Here we investigate one-photon single-ionization of both hydrogen and helium atoms by synchronous, chirped laser pulses in the configuration where one pulse is linearly polarized along the propagation direction of another pulse that is circularly polarized. For pulses of identical chirp, the PMD is found to exhibit a monopole (horseshoe-like) pattern. For differently chirped pulses, single-arm reversible spirals resembling the patterns of a snake biting its own tail (Ouroboros patterns) emerge in the PMD. This new type of spirals is controlled by changing the chirp amounts, pulse duration, helicity, and ellipticity of the second pulse. These results are valid for any S-state atom, as illustrated here for hydrogen and helium.

[1] J.M. Ngoko Djiokap, S.X. Hu, L.B. Madsen, N.L. Manakov, A.V. Meremianin, A.F. Starace, Phys. Rev. Lett. \textbf{115}, 113004 (2015)

[2] D. Pengel, S. Kerbstadt, D. Johannmeyer, L. Englert, T. Bayer, and M. Wollenhaupt, Phys. Rev. Lett. \textbf{118}, 053003 (2017)

[3] J. M. Ngoko Djiokap, A. V. Meremianin, and N. L. Manakov, Phys. Rev. A \textbf{103}, 023103 (2021)

[4] N. J. Strandquist, Jr. and J. M. Ngoko Djiokap, Phys. Rev. A \textbf{106}, 043110 (2022)

[5] L. Pedersen and J. M. Ngoko Djiokap, Manuscript submitted to Phys. Rev. A in October 2023.