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Nonlinear ionization of organic molecules in high intensity laser fields
1Femtosecond Science Program, Steacie Institute for Molecular Science, National Research Council, 100 Sussex Drive, Ottawa, Ontario, Canada K1A 0R6.
Physical Review Letters
|September 16, 2000
Summary
Organic molecules exhibit higher saturation intensities during intense laser pulse interactions than predicted by atomic ionization potentials. This study investigates the ionization dynamics of complex media using femtosecond laser pulses.
Area of Science:
- Physical Chemistry
- Atomic and Molecular Physics
- Nonlinear Optics
Background:
- Understanding the ionization dynamics of complex media is crucial for applications involving intense laser-matter interactions.
- Previous studies on dielectric breakdown with femtosecond pulses show similar high saturation intensities.
- The ionization behavior of organic molecules under intense laser fields requires further investigation.
Purpose of the Study:
- To investigate the ionization of 23 organic molecules using intense 40 fs, 0.8 µm laser pulses.
- To determine the ionization saturation intensities for these molecules and compare them to atomic expectations.
- To explore the factors influencing molecular ionization, excluding molecular alignment dependence.
Main Methods:
- Interaction of 23 organic molecules with intense, ultrashort (40 fs) laser pulses at 0.8 µm wavelength.
- Measurement of ionization saturation intensities.
- Analysis of intensity-dependent ionization yields to identify the range between single and multiple ionization.
Main Results:
- All studied organic molecules reached saturated ionization at higher intensities than expected based on their ionization potentials.
- The observed high saturation intensities are reminiscent of dielectric breakdown phenomena with femtosecond pulses.
- Molecular alignment with the laser field was ruled out as the cause for the elevated saturation intensities.
- A notable intensity range exists between complete single ionization and the onset of subsequent electron removal for all molecules.
Conclusions:
- Organic molecules exhibit distinct ionization saturation behaviors compared to atoms under intense ultrashort laser fields.
- The ionization process in complex media is complex and not solely dependent on ionization potential or molecular alignment.
- The identified intensity window for single ionization is significant for controlling laser-induced processes in organic materials.