单层TiO2/SiO2光学薄膜减散射理论与实验探究

Theoretical and Experimental Study on Scattering Reduction of Single-layer TiO2/SiO2 Optical Films

目的降低单层光学薄膜的散射损耗。方法通过相干散射理论研究,给出了单层光学薄膜减散射的理论依据。利用电子束热蒸发技术在K9玻璃上分别镀制了单层光学厚度为λ/2的TiO2和λ/4的SiO2薄膜,并通过改变工艺对薄膜的表面粗糙度进行了调控,利用horos散射仪分别测量了镀膜前后光学元件表面的双向反射分布函数。结果对于光学厚度为λ/2的单层TiO2薄膜,当薄膜上下界面粗糙度比值为0.7时,减散射效果明显优于比值为0.6和0.9,且比值越接近0.71,减散射效果越明显。对于光学厚度为λ/4的单层SiO2薄膜,当薄膜上下界面粗糙度比值为0.7时,减散射效果明显优于比值为0.8和1.4,且比值越接近0.13,减散射效果越明显。结论单层光学薄膜减散射条件不仅与光学薄膜的界面粗糙度有关,而且与薄膜光学厚度和膜料折射率也有着密切的关系。对于特定光学厚度的单层TiO2和SiO2薄膜,当薄膜上下界面的粗糙度比值满足减散射区间时,都可以实现减散射的效果,且比值越接近最佳减散射比值,减散射的效果越好。此外,在一定条件下,薄膜表面粗糙度大于基底表面粗糙度时,也有可能实现减散射的效果。

The work aims to reduce the scattering loss of single-layer optical films. The theoretical basis of the scattering reduction of single-layer optical films was proposed according to the theory of coherent scattering. A single layer of TiO2 with optical thickness λ/2 and SiO2 with optical thickness λ/4 were respectively deposited on K9 glass by electron beam thermal evaporation technique. The surface roughness of the film was adjusted by changing the process, and the horos scattering instrument was used to measure the bidirectional reflection distribution function on the surface of the optical element before and after coating. For the single-layer TiO2 film with optical thickness λ/2, when the ratio of the upper and lower interface roughness of the film was 0.7, the scattering reduction effect was obviously better than that with the ratio of 0.6 and 0.9, and the closer the ratio was to 0.71, the more obvious the scattering reduction effect was. For the single-layer SiO2 film with optical thickness λ/4,when the ratio of the upper and lower interface roughness of the film was 0.7, the scattering reduction effect was obviously better than that with the ratio of 0.8 and 1.4, and the closer the ratio was to 0.13, and the more obvious the scattering reduction effect was. The scattering resistance of the single-layer optical film is not only related to the interface roughness of the optical film, but also closely related to the optical thickness of the film and the refractive index of the film. For single-layer TiO2 and SiO2 films with specific optical thicknesses, when the roughness ratio of the upper and lower interfaces of the film satisfies the subtraction scattering interval, the effect of subtraction scattering can be achieved, and the closer the ratio is to the optimal subtraction ratio, the better the effect of subtract scattering is. Under certain conditions, when the surface roughness of the film is greater than the surface roughness of the substrate, it is also possible to achieve the effect of reducing the scattering.