Theoretical Foundation for Interface-Specific Hyper-Rayleigh Scattering in Uniaxial Chiral Assemblies

Area of Science:

• Nonlinear Optics
• Materials Science
• Biophysics

Background:

• Second Harmonic Generation (SHG) microscopy is valuable for analyzing heterogeneous materials like tissues and powders.
• Structural heterogeneity causes signal decoherence, challenging polarization analyses that assume pure signal polarization.
• Existing models for hyper-Rayleigh scattering (HRS) primarily address isotropic systems, not lower symmetry assemblies.

Purpose of the Study:

• To develop a mathematical framework for interpreting the incoherent component of SHG signals from uniaxially oriented assemblies.
• To extend the theory of HRS to include both achiral and chiral uniaxial systems.
• To explore the potential for new chiral-specific observables within the incoherent SHG response.

Main Methods:

• Developed a general theory for hyper-Rayleigh scattering (HRS) in uniaxially oriented assemblies.
• Included analysis for both achiral and chiral uniaxial systems.
• Investigated the symmetry properties of incoherent chiral contributions to SHG.

Main Results:

• The framework successfully interprets incoherent SHG signals from uniaxially oriented assemblies.
• Predicted the observation of electric dipole-allowed chiral-specific signals within the incoherent SHG component of chiral assemblies with polar, uniaxial symmetry.
• Demonstrated that these incoherent chiral contributions have distinct symmetry properties compared to coherent SHG chiral sensitivity.

Conclusions:

• The developed theory provides a method for analyzing decoherent SHG signals in heterogeneous and low-symmetry systems.
• The prediction of new incoherent chiral signals opens avenues for surface-specific and chiral-specific nonlinear optical analysis.
• This work offers insights into chiral SHG microscopy of biological tissues and suggests new experimental strategies.