The effect of orbital symmetry on high harmonic generation in molecules

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The effect of orbital symmetry on high harmonic
generation in molecules
Shambhu Ghimire, Bing Shan, and Zenghu Chang
J. R. Macdonald Laboratory
Kansas State University Manhattan, KS
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High harmonic generation
Step1 Ionization Step2 Acceleration Step3
Recombination
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High harmonic generation Effect of ellipticity on
atoms

• Laser is linearly polarized

HHG emission

• Laser is circularly polarized

y
x
No HHG emission
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Motivation

• Weather the molecules behaves same as the atoms
  for the ellipticity dependence of HHG or not??
• Does the orbital symmetry of molecules plays any
  role in ellipticity dependence of HHG
• Application to atto-second pulse generation

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High harmonic generationExperimental Setup
Kansas Light Source 4 mJ, 25fs 0.8 mm
MCP Phosphor
Gas nozzle
CCD
Grating
Filter
HHG Spectrum
HHG Spectrum
I1014 W/cm2
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The effect of orbital symmetry Slower dependence
for anti-bonding
Experimental results
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Previous workHigh harmonic generationEffect of
ellipticity on molecules
Harmonic yield decreases slower in molecules
??
Flettner et al, Eur. Phys. J. D, 21, 115 (2002)
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Orbital symmetry in molecules Wave function in
real space
N2

• Bonding (N2)

• Anti-Bonding (O2)

O2
Lein, J. Phys. B 36(2003)
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Orbital symmetry in molecules Wave function in
momentum space
N2

• Bonding

Ey
No HHG emission

• Anti-Bonding

O2
HHG emission
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Simulation resultslower dependence for
anti-bonding
Dr. Changs simulation
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Summary

• Molecules behaves differently than atoms for
  ellipticity dependence of HHG
• For near cutoff harmonics, O2 is less sensitive
  to ellipticity than N2.
• The difference between O2 and N2 is explained by
  the parity of molecules.
• Simulation results agrees qualitatively with the
  experiments

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