Fig.1 The flowchart of the RAM for obtaining the RI of thin films at a wavenumber ka
Y. Jin, B. Song*,et al. OPTICS EXPRESS 25(25):31273-31280(2017).
The well-known Swanepoel method was often used to obtain the refractive index (RI) of thin films at the wavenumber values corresponding to the extremes of the transmission interference fringes. But it is difficult to accurately obtain the RI of chalcogenide thin films, especially at arbitrary wavenumber. Recently, Y. Jin and B. Song et al. proposed a regional approach method (RAM) here to extend Swanepoel method to arbitrary wavenumber. In the RAM the RI at arbitrary wavenumber was determined through dynamic matching. The calculated values were used to match the experimental transmittance. The accuracy of the RI is better than 0.5%. The RI of a well-known film was obtained by the RAM. And the results are in great agreement with the true values of the RI of the film which indicates the correctness and effectiveness of the RAM. Moreover, the transmission spectrum of Ge-Sb-Se film was measured in the ultra-broadband range of 2000-18000 cm-1 (555-5000 nm), and finally the RI of the film was obtained at the 22 wavenumbers of the spacer 600 cm-1 by the RAM.
Fig.2 The transmittance curve T' (black full curve) of a 1μm film. The inset shows the plot of transmittance versus interference order