扩展柯西色散模型是表征混合液晶在可见光至红外光谱的通用双折射率色散模型,然而随着混合液晶的应用范围进入紫外光谱区,扩展柯西色散模型不能很好地表征混合液晶在该波长范围内的双折射率色散。为此,引入Sellmeier模型表征混合液晶在紫外至红外光谱的双折射率色散,并利用光谱椭偏仪精确测量混合液晶的双折射率数值,然后采用非线性拟合的方法求解Sellmeier模型系数。结果显示,扩展柯西模型的χ2检验数值为0.0349,而Sellmeier模型的χ2检验数值为0.0019,在标准测试波长589 nm以及紫外波段378 nm下,Sellmeier模型拟合值都更接近于实际测量值。通过实验和χ2检验对比分析可以证明,相比于扩展柯西色散模型,Sellmeier模型在紫外至红外波段具有更好的拟合效果。

The extended Cauchy model is a common model for describing the birefringence dispersion of liquid crystal mixture, however, in ultraviolet spectral ranges, the extended Cauchy model can not fit well with the experimental data. Here, we report a Sellmeier model for fitting the birefringence dispersion of liquid crystal mixture in a broad wavelength range from ultraviolet to near infrared. For this purpose, the principal birefringence values were accurately measured using spectroscopic ellipsometer and the Sellmeier coefficients were then obtained by a nonlinear fitting method. The results show that the χ2 of the Sellmeier model is 0.0019 and the χ2 of the extended Cauchy model is 0.0349. In addition, at the standard test wavelength of 589 nm and the ultraviolet wavelength of 378 nm, the fitting values show that the Sellmeier model were closer to the measured values. Both experimental result and χ2 test demonstrate that Sellmeier model has a better fit than extended Cauchy model.