Inversion of complex refractive index of natural kapok fibers based on BRDF scattering experiments and FDTD-QPSO method

The systematic research and development of fiber materials in the field of radiative regulation depends on the complex refractive index of the base material. However, there are some problems in the complex refractive index measurement of fiber materials based on ellipsometry, which makes the complex refractive index difficult to obtain and the measurement results may be problematic. Based on the first-principles calculations of electromagnetic scattering, an FDTD-QPSO method is proposed to invert the complex refractive index of the fiber by using the scattering characteristics. In this paper, the inversion of the complex refractive index of hollow fiber is studied and the appropriate inversion error interval is given. The results show that the method has good convergence effect and accuracy in the inversion calculation. Finally, the complex refractive index of natural kapok fiber is retrieved, and the inversion results are analyzed by combining K-K relations and the visible light color of actual kapok fiber. This work improves the complex refractive index inversion model of fiber materials and provides a certain numerical basis for studying the complex refractive index or radiative regulation mechanism of fiber materials.