Triple differential cross sections and nuclear recoil in two-photon double ionization of helium

Abstract

Triple differential cross sections (TDCS) for two-photon double ionization of helium are calculated using the method of exterior complex scaling both above and below the threshold for sequential ionization (54.4 eV). It is found that sequential ionization produces characteristic behavior in the TDCS that identifies that process when it is in competition with nonsequential ionization. Moreover we see the signature in the TDCS and nuclear recoil cross sections of "virtual sequential ionization" below the threshold for the sequential process.

Direct two-photon double ionization of H2

“…For further details about the models, see Refs. [18,52]. The relevant photoionization cross sections for the single ionization of H 2 was calculated by Sánchez and Martín [53].…”

Two-photon double ionization of helium: Evolution of the joint angular distribution with photon energy and two-electron energy sharing

“…For the discretization of the radial wave function R L l 1 ,l 2 (r 1 ,r 2 ,t), we employ the finite element discrete variable representation (FE-DVR), which has been successfully applied in numerous studies of the dynamics of few-electron atomic and molecular systems in intense laser fields (see, e.g., [38][39][40][56][57][58]). For details of the FE-DVR, please consult these previous works.…”

“…The TDCS provides a much more sensitive test of our code than does the total-ionization cross section, for which it is much easier to get a converged result [38]. We have chosen a photon energy of 42 eV for these tests since, for this energy, TPDI has been intensively studied by various theoretical methods [27,33,[38][39][40]. Although most previous results for the TDCS show qualitative agreement, the detailed shape and magnitude of the TDCS is very sensitive to the particular approximations used to solve the TDSE and to the particular laser parameters chosen.…”

“…Others present polar plots of the angular distribution of one electron resulting from integration of the triply differential cross section (TDCS) over all emission angles of the other electron [29,41,49]. Still others present nuclear recoil angular distributions [40,45,47]. As far as we know, the TDCS as a function of the emission angles of both ionized electrons [which we call here the joint angular distribution (JAD)] still needs to be thoroughly investigated.…”

Electron correlation in two-photon double ionization of helium from attosecond to XFEL pulses

“…With the advent of intense XUV pulses, the focus has shifted from single-photon double ionization [13][14][15][16][17] and intense-IR laser ionization by rescattering ( [18][19][20] and references therein) to multiphoton ionization. Two-photon double ionization (TPDI) has recently received considerable attention, both in the so-called "nonsequential" or "direct" regime (39.5 eV < ω < 54.4 eV), where the electrons necessarily have to share energy via electron-electron interaction to achieve double ionization [21][22][23][24][25][26][27][28][29][30][31][32][33][34], and in the "sequential" regime ( ω > 54.4 eV), where electron-electron interaction is not a priori necessary [11,[35][36][37][38][39][40].…”