ELFT HÍRADÓ

[Zimányiné Horváth Vera <Vera.Horvath AT eli-alps.hu>]

Előadó:                Debobrata Rajak (ELI ALPS)
Cím:                      Chiral molecules in strong laser fields

Helyszín:             az ELI ALPS konferenciaterme (Szeged, Wolfgang Sandner 
utca 3.)
Időpont:             2023. június 16., 9 óra


Az előadás rövid összefoglalója:
Light induced chemical processes are mediated by electronic interactions, 
which happens from atto-femto-pico second timescales, and are sensitive to 
the molecular structure. With advances in femto-second laser technology it 
has become possible to reach electric field values similar to the 
atomic/molecular binding potential. When an atom/molecule is exposed to such 
intense electromagnetic fields the potential barrier of the atom/molecule is 
considerably modified by the electromagnetic field. This modification is a 
dynamical process (see Fig 1.), occurring as the electromagnetic field 
oscillates, i.e. on the attosecond timescale (it takes only ~667 as for a 
visible electric field to go from its peak to zero). At the maximum of the 
laser field (Fig 1. a), the molecular potential barrier is lowered 
significantly and the electrons can tunnel out of this reduced barrier into 
the continuum (Fig 1. a 1). These tunnelled electrons are then driven by the 
oscillating laser field and can follow different trajectories (Fig 1. a 2). 
Some of them can be driven back to the ionic core, leading to a variety of 
processes: re-scattering, or recombination back to the ion emitting an XUV 
photon, or even diffraction from the molecular potential itself (Fig 1. b). 
These phenomena, referred to as "self-imaging", enable measuring structural 
and dynamics information with unprecedented resolutions - Angströms and 
attoseconds. However, as the complexity of the target increases, deciphering 
the information becomes more difficult, such that the majority of 
self-imaging measurements have up to now been restricted to small systems 
(diatomics, triatomics).

In this work, we investigate the sensitivity of self-imaging to molecular 
chirality. We measure the 3D photoelectron angular distributions resulting 
from the photoionization of fenchone and alpha-pinene molecules by a strong 
infrared laser field. When the field is circularly polarized, the electron 
distribution is asymmetric relative to the laser propagation axis: more 
electrons are ejected forward or backward, depending on the handedness of the 
molecule and the incident light. This chiroptical process, called 
Photo-Electron Circular Dichroism, is a pure electric dipole effect, leading 
to asymmetries in the few % range. When we switch the polarization state to 
elliptical, we observe the emergence of much higher energy electrons, which 
have been driven back towards their parent ion by the laser field before 
diffracting on the potential. We observe a strong forward-backward asymmetry 
in these diffracted electrons, and we show that this chiral laser-induced 
electron diffraction is very sensitive to the molecular structure. Last, we 
switch to linearly polarized laser pulses, and measure a chirosensitive 
rotation of the photoelectron angular distribution around the light 
propagation direction. This effect is interpreted as the result of the action 
of the laser magnetic field on the electron trajectories.
[cid:image002.png AT 01D99D2D.2170F3C0]

Figure 1. Dynamical processes involved in strong-field ionization: a) At peak 
electric field the electrons tunnels out of the modified potential barrier, 
b) when the electric field reverses sign in the next half cycle these 
electrons maybe driven back to ionic core leading to re-scattering, 
recombination or diffraction.

A szeminárium az alábbi link használatával online is meghallgatható:
https://teams.microsoft.com/l/meetup-join/19%3ameeting_NTQzNDY0NGItOGY4Zi00MGMxLWFmM2QtNDkyYjM5MjI5YTUw%40thread.v2/0?context=%7B%22Tid%22%3A%22b207389a-c5cb-4cb0-a1ad-227b94e96448%22%2C%22Oid%22%3A%22c993efcb-59ae-4652-9f68-d7a313727128%22%2C%22IsBroadcastMeeting%22%3Atrue%2C%22role%22%3A%22a%22%7D&btype=a&role=a


Minden érdeklődőt szívesen látunk.


ZIMÁNYINÉ HORVÁTH Vera
Látogatóközpont-vezető

ELI ALPS, ELI-HU Non-Profit Ltd.
H-6728 Szeged, Wolfgang Sandner utca 3.
Mobil: +36 70 491 14 12
E-mail: Vera.Horvath AT eli-alps.hu<http://Vera.Horvath AT eli-alps.hu/>
Honlap: www.eli-alps.hu<http://www.eli-alps.hu/>
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