2 XUV Lasers for Ultrafast Electronic Control in H 2
45
ferences between energy-degenerate paths) or the broad bandwidth of the ultrashort
pulses.
2.6 Future Perspectives
A large diversity of photoionization problems has been explored, both theoretically
and experimentally, using as prototypical molecules H 2 and D 2 . As it has been
widely discussed in Sects. 2.2 and 2.3, the last decade has undergone a sprout of
studies on processes induced by ultrafast pulsed radiation, prompted by the new
XFEL facilities and rapid developments of HHG techniques. These sources nowadays allow to explore fundamental problems in atomic and molecular physics at
their intrinsic electronic and nuclear time scales. For instance, a substantial number of works have employed pump-probe set-ups, with pulses as short as a few
hundreds of as, to generate time-resolved images of electronic and nuclear wave
packets. However, further theoretical and experimental efforts are required to prove
the ability of these technologies to not only trace, but drive and steer the electron
and nuclear dynamics in atoms, molecules and, eventually, in larger systems.
This goal can only be reached through a deep knowledge of the underlying
physics in the laser-induced phenomena, which makes the hydrogen molecules, i.e.
the smallest multielectron molecular targets, the perfect candidates. As we have
seen, autoionization studies, in which doubly excited states are populated by absorption of one or two photons, have already shed some light on the role of electron
correlation combined with the nuclear motion. Moreover, existent robust theoretical methods, with demonstrated capability to predict laser-induced phenomena in
hydrogen molecules, have recently given strong support for experimental measurements that have only become available with the new radiation sources. Example of
those are XUV pump–IR probe experiments that have been able to achieve electron
localization in H 2 and D 2 [37, 38], and XUV pump–XUV probe schemes that map
nuclear wave packets created in H
+
2 into the full break up channels [33, 34]. The use
of these targets as benchmarks for novel experimental set-ups require constant theoretical input. Theoretical simulations are also valuable to predict novel phenomena
that may arise in laser-molecule interactions [51, 52] and to explore problems as
coherent control in multiphoton ionization [94]. However, despite the flexibility and
wide applicability of the methods described in this chapter, many interesting problems, even for simple molecules, still need the development of new theoretical tools.
This is the case of studies on one- and few-photon double ionization processes, in
which both electrons are simultaneously ejected by direct photoabsorption, or sequential absorption processes. These investigations will bring a better understanding of electron correlation effects and are encouraged by the above mentioned XUV
pump–XUV probe experiments [33, 34]. In this context, theoretical and computational efforts are being currently devoted to tackled double ionization problems in
hydrogen molecules. Such methodologies are also expected to be useful to explore
non-linear effects induced by strong IR fields. Accurate descriptions for these problems are still scarce and will be the subject of further work in the near future.
45
ferences between energy-degenerate paths) or the broad bandwidth of the ultrashort
pulses.
2.6 Future Perspectives
A large diversity of photoionization problems has been explored, both theoretically
and experimentally, using as prototypical molecules H 2 and D 2 . As it has been
widely discussed in Sects. 2.2 and 2.3, the last decade has undergone a sprout of
studies on processes induced by ultrafast pulsed radiation, prompted by the new
XFEL facilities and rapid developments of HHG techniques. These sources nowadays allow to explore fundamental problems in atomic and molecular physics at
their intrinsic electronic and nuclear time scales. For instance, a substantial number of works have employed pump-probe set-ups, with pulses as short as a few
hundreds of as, to generate time-resolved images of electronic and nuclear wave
packets. However, further theoretical and experimental efforts are required to prove
the ability of these technologies to not only trace, but drive and steer the electron
and nuclear dynamics in atoms, molecules and, eventually, in larger systems.
This goal can only be reached through a deep knowledge of the underlying
physics in the laser-induced phenomena, which makes the hydrogen molecules, i.e.
the smallest multielectron molecular targets, the perfect candidates. As we have
seen, autoionization studies, in which doubly excited states are populated by absorption of one or two photons, have already shed some light on the role of electron
correlation combined with the nuclear motion. Moreover, existent robust theoretical methods, with demonstrated capability to predict laser-induced phenomena in
hydrogen molecules, have recently given strong support for experimental measurements that have only become available with the new radiation sources. Example of
those are XUV pump–IR probe experiments that have been able to achieve electron
localization in H 2 and D 2 [37, 38], and XUV pump–XUV probe schemes that map
nuclear wave packets created in H
+
2 into the full break up channels [33, 34]. The use
of these targets as benchmarks for novel experimental set-ups require constant theoretical input. Theoretical simulations are also valuable to predict novel phenomena
that may arise in laser-molecule interactions [51, 52] and to explore problems as
coherent control in multiphoton ionization [94]. However, despite the flexibility and
wide applicability of the methods described in this chapter, many interesting problems, even for simple molecules, still need the development of new theoretical tools.
This is the case of studies on one- and few-photon double ionization processes, in
which both electrons are simultaneously ejected by direct photoabsorption, or sequential absorption processes. These investigations will bring a better understanding of electron correlation effects and are encouraged by the above mentioned XUV
pump–XUV probe experiments [33, 34]. In this context, theoretical and computational efforts are being currently devoted to tackled double ionization problems in
hydrogen molecules. Such methodologies are also expected to be useful to explore
non-linear effects induced by strong IR fields. Accurate descriptions for these problems are still scarce and will be the subject of further work in the near future.