Spin and orbital angular momentum probing of nanoscale polycrystalline texture in complex biological medium

Understanding structural anisotropy at the nanoscale is essential for the development of advanced photonic and quantum materials. We present a novel optical framework leveraging the combined spin and orbital angular momentum (SAM and OAM) of light for the characterization of polycrystalline and nanostructured materials, including biological analogs. Structured light beams with engineered polarization and helical phase are shown to be highly sensitive to local grain orientation, boundary domains, and refractive index discontinuities typical of complex crystalline or fibrous media. By exploiting the phase coherence and topological features of OAM beams, alongside polarization singularities, we demonstrate non-invasive, label-free detection of polycrystalline textures through their unique scattering and interference signatures. The approach is validated in model media and extended to biologically relevant tissues with pseudo-crystalline order. This photonic method reveals new pathways for spin-OAM-assisted optical sensing in materials science and biophotonics, offering a powerful diagnostic tool for real-time monitoring of nanoscale structural organization in optoelectronic, quantum,