Stokes vector based polarization resolved second harmonic microscopy of starch granules.

Area of Science:

• Optics and Photonics
• Biophysics
• Materials Science

Background:

• Starch granules possess a unique concentric shell structure.
• This structure acts as a natural photonic crystal, influencing light interactions.
• Second Harmonic Generation (SHG) is a nonlinear optical process sensitive to material structure and polarization.

Purpose of the Study:

• To measure and analyze the polarization state of SHG signals from starch granules.
• To extract various polarization parameters (DOP, DOLP, DOCP, anisotropy) from SHG images.
• To investigate the relationship between starch granule structure and SHG polarization properties.

Main Methods:

• Utilized a four-channel photon counting based Stokes-polarimeter for SHG signal measurement.
• Acquired 2D second harmonic Stokes images of starch granules.
• Analyzed polarization parameters from the generated images.

Main Results:

• Successfully extracted degree of polarization (DOP), degree of linear polarization (DOLP), degree of circular polarization (DOCP), and anisotropy.
• Observed that the concentric shell structure leads to similar SHG quantum efficiency irrespective of incident polarization.
• Demonstrated the potential to infer input beam polarization states from SHG micrographs.

Conclusions:

• The photonic crystal nature of starch granules influences SHG polarization.
• SHG imaging provides a method to characterize starch granule structure and incident light polarization.
• This technique offers insights into the optical properties of biological materials.