Pulse Propagation Effects in Optical 2D Fourier-Transform Spectroscopy: Theory

Area of Science:

• Atomic, Molecular, and Optical Physics
• Quantum Optics
• Spectroscopy

Background:

• Two-dimensional Fourier transform (2DFT) spectroscopy is a powerful tool for probing molecular dynamics.
• Understanding spectral distortions is crucial for accurate interpretation of experimental data, especially at high optical densities.
• Previous studies often focused on low optical density regimes, limiting insights into complex spectral behaviors.

Purpose of the Study:

• To simulate and analyze spectral distortions in rephasing 2DFT spectra of atomic rubidium vapor.
• To investigate the effects of increasing optical density on spectral features, including peak splitting and coherent transient twisting.
• To compare simulation results with experimental data and explore methods for mitigating distortions.

Main Methods:

• Solving Maxwell's equations in the three-dimensional frequency domain.
• Calculating rephasing 2DFT spectra using a homogeneous Bloch line shape model.
• Simulating experimental distortions arising from pulse propagation and varying experimental conditions like beam overlap and pseudo-time domain filtering.

Main Results:

• At high optical densities (up to 3), spectral distortions manifest as peak broadening, splitting, and novel coherent transient twisting.
• These distortions depend on waiting time and excited state lifetime, unlike the low optical density limit.
• Simulations quantitatively reproduced experimental observations of peak splitting and twisting in rubidium vapor spectra.

Conclusions:

• High optical density introduces significant distortions in 2DFT spectra, leading to complex phenomena like coherent transient twisting.
• The Bloch model, when accounting for finite optical density effects, accurately predicts these distortions.
• 2DFT rephasing spectra are susceptible to propagation distortions, unlike 2DFT relaxation spectra, and require careful consideration of experimental parameters.