Second harmonic generation in two different arrangement of type I collagen on nonlinear microscopy

Second harmonic generation (SHG) microscopy has emerged as a powerful tool for biomedical research, especially in fibrosis-related disease studies. In this letter, two different arrangement models were established to compare SHG in type I collage, which is a major risk factor for fibrotic diseases. Different models result in distinct SHG intensity curves, which are functions of polarization angle. Based on those models, the influences of different scatters array and incident polarization on SHG in biological tissues were discussed. For practical application, this theoretical approach can guide us to judge the array pattern or the slice type of biological tissues and lead us to analyze the severity of collage diseases. Moreover, the relationship between the SHG intensity and parameter ρ was revealed, which is closely related to the age of living organisms.