Spectral content and dispersion of hyper-Rayleigh scattering

Area of Science:

• Nonlinear optics
• Molecular spectroscopy
• Organic dyes

Background:

• Hyper-Rayleigh scattering (HRS) provides insights into molecular hyperpolarizability.
• Understanding light-matter interactions in organic dyes is crucial for optical applications.
• Two-photon fluorescence can compete with HRS, complicating spectral analysis.

Purpose of the Study:

• To investigate the spectral content of light scattered near the second harmonic for p-Nitroaniline and Disperse Red 1.
• To analyze the interplay between hyper-Rayleigh scattering and two-photon fluorescence.
• To determine the dispersion of the first hyperpolarizability for these organic dyes.

Main Methods:

• Utilized a high-intensity tunable picosecond infrared laser source.
• Measured spectral content of scattered light near the second harmonic.
• Employed a simple referencing technique to determine hyperpolarizability dispersion.

Main Results:

• Observed competing two-photon fluorescence and hyper-Rayleigh peaks in Disperse Red 1.
• Found that dephasing can lead to fluorescence dominating over HRS when the harmonic is near the linear absorption tail.
• Determined the dispersion of the first hyperpolarizability for both dyes, consistent with a two-level dispersion model.

Conclusions:

• The spectral response of organic dyes to nonlinear optical excitation is complex, involving competing processes.
• Hyper-Rayleigh scattering is sensitive to excited state dynamics and linear absorption properties.
• The two-level dispersion model adequately describes the observed hyperpolarizability dispersion in these dyes.