Probe Beam Dichroism and Birefringence in Stimulated Raman Scattering in Polyatomic Molecules

Area of Science:

• * Molecular Spectroscopy
• * Nonlinear Optics
• * Quantum Chemistry

Background:

• * Stimulated Raman Scattering (SRS) is a powerful technique for probing molecular vibrations.
• * Understanding polarization effects like dichroism and birefringence is crucial for accurate SRS analysis.
• * Previous theoretical models often simplified polarization states or propagation geometries.

Purpose of the Study:

• * To theoretically investigate dichroism and birefringence in polyatomic molecules undergoing SRS.
• * To derive general expressions for the polarization matrix change of a probe beam in an isotropic molecular sample.
• * To provide a framework for experimentally separating the contributions of dichroism and birefringence to the SRS signal.

Main Methods:

• * Theoretical derivation of general expressions for probe beam polarization change using spherical tensor operators.
• * Analysis of arbitrary polarization states and propagation directions for pump and probe beams.
• * Detailed consideration of near-collinear propagation geometry.

Main Results:

• * General expressions were derived for the polarization matrix of the probe beam transmitted through an SRS-excited molecular sample.
• * Dichroism and birefringence were shown to be related to the nonlinear optical susceptibility element $$.
• * A method using a polarization analyzer was proposed for experimentally separating these contributions.

Conclusions:

• * The theoretical framework allows for the separation of dichroism and birefringence in SRS.
• * The findings are applicable to both off-resonant and resonant SRS processes.
• * Experimental verification using Stokes polarization parameters is facilitated by the derived expressions.