采用光谱型椭偏仪(SE)和分光光度计分别测量了超薄类金刚石(DLC)薄膜和非晶硅(a-Si)薄膜的椭偏参数（y和D）和透射率T。由于薄膜的厚度与折射率、消光系数之间存在强烈的相关性，仅采用椭偏参数拟合，难以准确得到薄膜的光学常数。如果加入透射率同时进行拟合（以下简称SE+T 法），可简单、快速得到薄膜的厚度和光学常数。但随机噪声、样品表面的轻微污染或衬底上任何小的吸收都可能影响SE+T 法拟合的光学常数的准确性。因此将SE+T 法和光学常数参数化法联用，实现DLC、a-Si薄膜光学常数的参数化，以消除测量数据中的噪声对光学常数的影响。结果显示，联用时的拟合结果具有更好的唯一性，而且拟合得到的光学常数变得平滑、连续且符合Kramers-Kronig (K-K)关系。这种方法特别适合于精确表征厚度仅为几十纳米的非晶吸收薄膜的光学常数。

Spectroscopic ellipsometry (SE) and spectrophotometer are used to measure the ellipsometric parameters (y and D ) and transmittance of ultrathin diamond like carbon (DLC) film and amorphous silicon (a-Si) film respectively. Accurate determination of optical constants and thickness of DLC film and a- Si film is a difficult problem when ellipsometric parameters are used independently. It is due to the strong statistical correlation which exists between the optical constants and thickness of the film when these parameters are adjusted to fit the experimental ellipsometric parameters. By simultaneous fitting ellipsometric parameters and transmittance (SE+T), thickness and optical constants can be obtained easily and rapidly. However, noise, minor contamination on the film surface or any small absorption in the substrate will be mixed into the film′s optical constants. In order to determine the optical constants of ultrathin DLC and a-Si film accurately, the optical constants are parameterized by combining SE+T and optical constant parameterization approach. The results show that the adopted method is able to uniquely and accurately measure optical constants from a unique solution while maintaining smooth, continuous, and often Kramers-Kronig (K-K) consistent optical properties for the ultrathin DLC film and a-Si film. This method is expected to be of value for optical property measurement of other amorphous films with thickness of just a few tens of nanometers.