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Multiphoton-excited visible emission by serotonin solutions
Photochemistry and Photobiology
|June 1, 1997
Summary
Nonlinear excitation of serotonin (5HT) creates a blue-green light-emitting product. This requires six-photon absorption, involving a four-photon excitation followed by two-photon emission, likely via photoionization.
Area of Science:
- Photochemistry
- Nonlinear Optics
- Biophysics
Background:
- Serotonin (5HT) exhibits characteristic UV fluorescence.
- Nonlinear optical phenomena enable multi-photon absorption processes.
Purpose of the Study:
- To investigate the nonlinear excitation of serotonin in aqueous solution.
- To characterize the photoproducts and emission mechanisms involved.
Main Methods:
- Nonlinear excitation using near-IR photons from a titanium: sapphire laser.
- Diffusional steady-state and transient measurements of emission.
- Analysis of excitation intensity dependence and emission spectra.
Main Results:
- Visible emission scales with the sixth power of excitation intensity, indicating six-photon absorption.
- A two-step nonlinear process was identified: four-photon absorption followed by two-photon emission.
- Photoionization is proposed as the primary mechanism for photoproduct generation.
Conclusions:
- Serotonin undergoes photochemical transformation via multi-photon absorption to a visible-emitting photoproduct.
- The two-photon emission action cross section has a minimum bound of ~10^-51 cm^4 s photon^-1.
- Observed intensities are achievable with advanced laser systems and are below water's dielectric breakdown threshold.