阐述了包络法、色散模型拟合法、K-K变换法等常用的光学常数获取方法,并分析了每种方法的局限性。针对光学薄膜普遍在中红外波段存在水吸收,而导致其光学常数难以准确计算的特点,在以上几种方法的基础上,提出了一种改进的计算方法,并对该方法进行了推导。采用离子束溅射技术,制备了单层Ta2O5、Al2O3和Nb2O5薄膜,并用该方法计算了薄膜中红外波段的光学常数,结果显示,三种薄膜的消光系数均在2.7～4 μm波段存在明显峰值,表明用该方法计算的光学常数,能清晰地反映薄膜水吸收的特性,较常规方法具有更高的精度。

Commonly used methods to acquire optical constants, such as envelope method, dispersion model fitting and K-K transform are introduced. The limitations of these methods are analyzed. To overcome the difficulty of calculating optical constants caused by water absorption in the mid-infrared range of optical thin films, an improved method is developed and the mathematical deduction is given. Single layer Al2O3, Nb2O5 and Ta2O5 films are prepared by ion beam sputtering deposition, and the optical constants of these films are calculated by the new method. Results show that the extinction coefficients of the three kinds of films have an obvious peak in 2.7～4 μm region. This method can clearly reflect the water absorption in thin films, and has indicating higher precision than traditional methods.