The well-known method presented by Swanepoel can be used to determine the refractive index dispersion of thin films in the near-infrared region from wavelength values at maxima and minima, only, of the transmission interference fringes. In order to extend this method into the mid-infrared spectral region (our measurements are over the wavelength range from 2 to 25Â Âµm), the method is improved by using a two-term Sellmeier model instead of the Cauchy model as the dispersive equation. Chalcogenide thin films of nominal batch composition As40Se60 (at.%) and Ge16As24Se15.5Te44.5 (at.%) are prepared by a hot-pressing technique. The refractive index dispersion of the chalcogenide thin films is determined by the improved method with a standard deviation of less than 0.0027. The accuracy of the method is shown to be better than 0.4% at a wavelength of 3.1Â Âµm by comparison with a benchmark refractive index value obtained from prism measurements on Ge16As24Se15.5Te44.5 material taken from the same batch.
- Chalcogenide glasses
- Refractive index
Fang, Y. Z., Jayasuriya, D., Furniss, D., Tang, Z. Q., Sojka, M., Markos, C., Sujecki, S., Seddon, A. B., & Benson, T. M. (2017). Determining the refractive index dispersion and thickness of hot-pressed chalcogenide thin films from an improved Swanepoel method. Optical and Quantum Electronics, 49(7), . https://doi.org/10.1007/s11082-017-1057-9