Novel approaches in HHG spectroscopy Caterina Vozzi Istituto di - - PowerPoint PPT Presentation
Novel approaches in HHG spectroscopy Caterina Vozzi Istituto di Fotonica e Nanotecnologie Milano (Italy) ICTP Winter School 07/02/2018 Outline A few reminders of HHG spectroscopy the study of electron correlation in xenon:
Caterina Vozzi Istituto di Fotonica e Nanotecnologie Milano (Italy)
07/02/2018 ICTP Winter School
2
experiments and interpretation
development of the molecular imaging lab @ IFN-CNR
3
valence shell via tunnel ionization
laser field
released through the emission of a XUV photon
4
hνcutoff = Ip+3.17Up where Up ~ E2λ2
but... generation yield ~λ-α with α~5-6
5
valence shell
6
ionization time ts– τs recombination time ts photon energy ħΩ through the saddle point approximation
7 Shafir et al. Nature 485 85, 343 (2012)
The attosecond nature of the process is mapped into the HHG spectrum! Each saddle point solution defines a quantum trajectory
8
it is not a complex system...but:
9
gia iant resona sonance aroun
100 eV V
first channel: the returning electron recombines directly with the 5p electron vacancy second channel: the returning electron promotes an electron of the 4d inner shell to the 5p valence shell via inelastic scattering and then it recombines with the 4d electron vacancy
10
111, 233005 (2013)
11
12
Two possible polarization configurations: Parallel: Perpendicular:
half-wave plate @ 1500 nm
13
the symmetry between the two half cycles is broken this results in two classes of trajectories with two different cutoffs and ionization probabilities
cutoff 1 cutoff 2
14
cutoff 1 cutoff 2
cutoff1 cutoff2 Ionization rate 1 Ionization rate 2
SAE upper branch suppressed lower branch
Frolov et al., PRA 81, 063407 (2010)
15 Qualitative and quantitative agreement with TDCIS calculations when all 5p, 5s and 4d orbitals are interacting
5p 5p + 5s + 4d exp
time-dependent configuration interaction singles (TDCIS) calculations
by Stefan Pabst
16
the upper branch becomes visible in the HHG spectrum only when all 5p, 5s and 4d orbitals are interacting the GIANT RESONANCE counteracts the reduced ionization probability of the upper branch …Can we extract information on the electron- electron correlation from HHG spectra? In parallel polarization we cannot easily disentangle τs,ts, Ω
17
The second harmonic displaces the electron in the
direction, it acts as a gating which selects specific trajectories with a given energy There is an
phase delay φ between the two fields that maximizes the probability of recombination for each harmonic photon energy.
φ(Ω) is a measure of the recombination time of the electron tr
…it is a clock to probe dynamics!
18
(1) The xenon giant resonance gives access to the observation of unrevealed features:
it counteracts the reduced ionization probability of the upper branch
it enhances the contribution
(2) We measured the delay induced by the process in the energy region of the cutoff trajectories
the coulomb-exchange process. (3) Two-color HHG spectroscopy is sensitive to the phase of the dipole.
20
Dr Driv iving laser ser sour urce ce: <22 fs pulses 15 mJ energy 1 kHz repetition rate
the laser source
21
manipulating the light
Hig High ener energy OP OPA
1.2 2 – 3 µm
22
XUV XUV sp spec ectromet
detection VMI MI sp spec ectromet
for electrons up to 200 eV
Stefan Pabst
24
ASPIRE ITN
caterina.vozzi@cnr.it www.udyni.eu www.mi.ifn.cnr.it/research/ultrafast/molecularimaging