Time-resolved Chemical Imaging with infrared Lasers • Electron diffraction and X-ray diffraction cannot be used for time- resolved imaging at the femtoseconds level • Can use IR lasers to probe molecular structure? • First needs to identify the role of molecular structure in laser-induced phenomena: electron momentum spectra and HHG
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Time-resolved Chemical Imaging with infrared Lasers
Time-resolved Chemical Imaging with infrared Lasers. Electron diffraction and X-ray diffraction cannot be used for time-resolved imaging at the femtoseconds level Can use IR lasers to probe molecular structure? - PowerPoint PPT Presentation
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Time-resolved Chemical Imaging with infrared Lasers
• Electron diffraction and X-ray diffraction cannot be used for time-resolved imaging at the femtoseconds level • Can use IR lasers to probe molecular structure?
• First needs to identify the role of molecular structure in laser-induced phenomena: electron momentum spectra and HHG
•Retrieve the molecular structure (inverse scattering)
Tomography of Molecular Orbitals
•HHG from molecules via rescattering/recombination
•HHG depends on the target HOMO orbital
•Retrieve HOMO orbital from HHG via Tomography
Validity of the plane wave approximation: not adequate for typical returning electrons
PWA –Tomographic imaging of Itatani et al Nature 2004
(HHG)TDSE=(WP) (crs)exact
(HHG)SFA=(WP) (crs)PWA
Model: HHG= (wave packet) x (photo-recombination cross section) -- Electron wave packet is determined by the driving laser only
--- Compare two atomic systems with identical ionization potential Neon vs Scaled atomic hydrogen-- or from strong field approximation
Extract Photo-recombination cross sections from HHG— based on results from TDSE
4-cycle pulse
Electron wave Packets “derived” from HHG
Photoionization crs derived from HHG by comparing Ar vs H
Model for molecules
),()( ),(),()(~),( kii ekeWNdw
W: Returning electron wave-packet
σ: Photorecombination cross section
θ: Alignment angle (for molecule)
k: Electron momentum, k2/2=ω-Ip
W is largely independent of target for targets with similar Ip
Cooper minimum
Different lasers are usedPhoto-recombination can be extracted with high accuracy!
PhaseCross section
Cooper minimum
Ne: 1064 nm, 10.3 fs (FWHM), 2x1014 W/cm2
Wave-packet from the Lewenstein model is good!
Current SFA model not adequate (even for atoms!) For molecules, the interference minimum positions not correctly
predicted by SFA
Our strategy: use the wave-packet from SFA or TDSE for system with similar ionization potential