Quantitative Polarization-Resolved Second-Harmonic-Generation Microscopy of Glycine Microneedles

Second-harmonic generation (SHG) is a nonlinear optical process that can provide disease diagnosis through characterization of biological building blocks such as amino acids, peptides, and proteins. The second-order nonlinear susceptibility tensor chi((2))of a material characterizes its tendency to cause SHG. Here, a method for finding the chi((2))elements from polarization-resolved SHG microscopy in transmission mode is presented. The quantitative framework and analytical approach that corrects for micrometer-scale morphology and birefringence enable the determination and comparison of the SHG susceptibility tensors of beta- and gamma-phase glycine microneedles. The maximum nonlinear susceptibility coefficients ared(33) = 15 pm V(-1)for the beta andd(33) = 5.9 pm V(-1)for the gamma phase. The results demonstrate glycine as a useful biocompatible nonlinear material. This combination of the analytical model and polarization-resolved SHG transmission microscopy is broadly applicable for quantitative SHG material characterization and diagnostic imaging.