Probing Multiphoton Photophysics Using Two-Beam Action Spectroscopy

Area of Science:

• Nonlinear Optics
• Photophysics
• Spectroscopy

Background:

• Multiphoton absorption (MPA) is crucial for various applications but challenging to characterize due to low probabilities.
• Existing methods using optical emission for nonlinear absorption characterization have limitations.

Purpose of the Study:

• Introduce and validate two-beam constant emission intensity (2-BCEIn) spectroscopy for MPA characterization.
• Investigate nonlinear absorption in crystal violet lactone (CVL) across a transition from two-photon to three-photon absorption.

Main Methods:

• Developed and applied 2-BCEIn spectroscopy, a novel technique for nonlinear absorption studies.
• Studied CVL solutions at excitation wavelengths from 750 nm to 830 nm.
• Utilized a kinetic model incorporating intrapulse excited-state absorption.

Main Results:

• 2-BCEIn spectroscopy directly measures local exponents, overcoming dynamic range limitations of nonlinear fluorescence excitation (NFE).
• Demonstrated that nonlinear excitation of CVL at 800 nm involves more than simple two-photon and three-photon absorption.
• Successfully modeled complex photophysics, enabling determination of the ratio of three-photon to two-photon absorption cross sections.

Conclusions:

• 2-BCEIn spectroscopy offers significant advantages for characterizing complex multiphoton absorption processes.
• The technique provides insights into photophysical mechanisms not accessible by conventional NFE.
• Highlights the versatility of two-beam action spectroscopies for advanced optical studies.