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Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional π-conjugate Systems
Published on: February 10, 2020
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Vibrational line shape effects in plasmon-enhanced stimulated Raman spectroscopies
1Intel Corporation, 2501 NW 229th Ave., Hillsboro, Oregon 97124, USA.
The Journal of Chemical Physics
|November 21, 2021
Summary
A new density matrix model explains plasmon-enhanced (PE) stimulated Raman spectroscopies. This model reveals how plasmon enhancement influences spectral line shapes in PE-FSRS and PE-SRG/L, crucial for understanding these advanced techniques.
Area of Science:
- Physical Chemistry
- Spectroscopy
- Plasmonics
Background:
- Plasmon-enhanced (PE) spectroscopies offer enhanced sensitivity for molecular analysis.
- Understanding the theoretical underpinnings of PE nonlinear spectroscopies is crucial for their application.
- Previous models have not fully captured the temporal dynamics of plasmon-enhanced fields.
Purpose of the Study:
- To develop a comprehensive density matrix treatment for plasmon-enhanced stimulated Raman spectroscopies.
- To elucidate the origins of dispersive vibrational line shapes in PE-SRG/L and PE-FSRS.
- To analyze the influence of plasmon resonance and pulse characteristics on PE-FSRS.
Main Methods:
- A density matrix formalism is employed to describe the interaction of light with molecules under plasmonic enhancement.
- A Lorentz oscillator model is utilized to represent the time-dependent behavior of plasmon-enhanced optical fields.
- The theoretical framework is applied to plasmon-enhanced stimulated Raman Gain/Loss (PE-SRG/L), coherent anti-Stokes Raman scattering (PE-CARS), and femtosecond stimulated Raman spectroscopy (PE-FSRS).
Main Results:
- Dispersive vibrational line shapes in PE-SRG/L and PE-FSRS spectra are primarily attributed to the square of the complex optical field enhancement factor.
- The derived PE-FSRS intensity expression demonstrates dependencies on plasmon resonance, pulse characteristics (picosecond and femtosecond), and molecular vibrational properties.
- The absence of dispersive line shapes in PE spontaneous Raman spectroscopy is explained by differences in signal detection mechanisms.
Conclusions:
- The developed density matrix treatment provides a robust theoretical foundation for understanding plasmon-enhanced nonlinear molecular spectroscopies.
- The model accurately predicts spectral line shape features, particularly dispersive components, in PE-SRG/L and PE-FSRS.
- This work offers insights into optimizing experimental parameters for enhanced spectroscopic measurements.
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