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Dependence of the laser two-photon ionization process in solution on the laser pulse width
1Department of Molecular Science and Technology, Kyushu University, Fukuoka, Japan.
Analytical Chemistry
|May 17, 2001
Summary
Investigating laser two-photon ionization reveals distinct mechanisms based on pulse width. Ultrafast femtosecond lasers enable simultaneous two-photon processes, differing from picosecond stepwise ionization.
Area of Science:
- Physical Chemistry
- Atomic and Molecular Physics
- Laser Spectroscopy
Background:
- Laser two-photon ionization is a complex process.
- Understanding the ionization mechanism is crucial for various applications.
- The role of laser pulse width in ionization pathways requires clarification.
Purpose of the Study:
- To elucidate the mechanism of laser two-photon ionization.
- To differentiate between stepwise and simultaneous ionization pathways.
- To investigate the influence of laser pulse width on the ionization process.
Main Methods:
- Simultaneous irradiation using UV and IR laser beams.
- Varying laser pulse widths (300 ps and 100 fs).
- Observation of signal enhancement and molecular response at different wavelengths.
Main Results:
- Picosecond (ps) pulse widths indicated a stepwise ionization via a geminate pair state, evidenced by signal enhancement.
- Femtosecond (fs) pulse widths showed no signal enhancement, suggesting a simultaneous two-photon process.
- Intense signals were observed even for molecules lacking absorption at the laser wavelength with fs pulses.
Conclusions:
- Laser two-photon ionization proceeds via a stepwise mechanism with ps pulses.
- Ultrafast fs laser excitation facilitates a simultaneous two-photon ionization process.
- Detection limits are sensitive to laser fluctuations, impacting experimental precision.