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提出了一种同时测量强吸收衬底上薄膜厚度和折射率的方法。对生长于强吸收衬底上的透明薄膜,提出在该薄膜上镀一层薄金属,形成金属-薄膜-强吸收衬底的类波导结构。由于小角度入射光在强吸收衬底上具有较强的反射率,使该结构可容纳一系列共振模。利用自由空间耦合技术和导出的共振模模式本征方程,同时确定透明薄膜的厚度和折射率。实验中测量了硅衬底上制备的聚甲基丙烯酸甲酯(PMMA)薄膜的折射率和厚度,测量的相对误差均小于10-3。该方法具有简便、可靠、可测量任意折射率薄膜的优点。
A method for simultaneous measurement of film thickness and refractive index on strongly absorbing substrates is proposed. For a transparent film grown on a strongly absorbing substrate, a waveguide-like structure is proposed in which a thin metal layer is formed on the thin film to form a metal-film-strongly-absorbing substrate. Since small-angle incident light has a strong reflectivity on strongly absorbing substrates, the structure accommodates a series of resonant modes. Using the free-space coupling technique and the derived resonant mode intrinsic eigenvalue, the thickness and refractive index of the transparent film are determined simultaneously. In the experiment, the refractive index and thickness of polymethylmethacrylate (PMMA) thin films prepared on silicon substrate were measured. The relative errors of measurement were less than 10-3. The method has the advantages of simplicity, reliability, and measurability of an arbitrary refractive index film.