Material refractive indices in vacuum and air
OptiReOpt DLL is intended for the support of manufacture of arbitrary multilayer optical coatings. In the case of two-component optical coatings high and low index materials are typically referred to as H- and L- materials.
For some manufacturing processes layer materials refractive indices exhibit variations after the coating exposition to air environment. The main source of such variations is layer porosity. Refractive index variations due to other factors, like small chemical or structural changes, are also possible.
One should always keep in mind that on-line monitoring and on-line characterization are done in vacuum while manufactured optical coating is intended for use in quite different environment. For this reason reliable information about layer material refractive indices in vacuum and air is required for the successful on-line characterization and re-optimization.
It is highly recommended to perform special pre-investigation of layer material properties in vacuum and ambient environment. Using literature data on material refractive indices is dangerous because actual layer material indices are dependent on the type and parameters of the deposition process in use.
It is necessary to investigate not only layer material refractive indices but also layers bulk inhomogeneity. Even dense layers produced by energetic deposition processes often feature bulk inhomogeneity (usually bulk inhomogeneity of a positive type). Ignoring layers inhomogeneity may lead to the accumulation of errors in the course of the on-line characterization and to the loss of accuracy of thickness determination with the growing number of deposited layers.
We recommend using OptiChar and OptiRE programs of the OptiLayer software family for the detailed investigation of layer material properties in vacuum and air.
- A. V. Tikhonravov, M. K. Trubetskov, Online characterization and reoptimization of optical coatings, Proc. SPIE. 5250, Advances in Optical Thin Films 406 (2004)
- S. Wilbrandt, O. Stenzel, N. Kaiser, M.K. Trubetskov, and A.V. Tikhonravov, "In situ optical characterization and reengineering of interference coatings," Appl. Opt. 47, C49-C54 (2008).
- S. Wilbrandt, O. Stenzel, N. Kaiser, M. K. Trubetskov, and A. V. Tikhonravov, "On-line Re-engineering of Interference Coatings," in Optical Interference Coatings, OSA Technical Digest (CD) (Optical Society of America, 2007), paper WC10.
- J. Oliver, A. Tikhonravov, M. Trubetskov, I. Kochikov, and D. Smith, "Real-Time characterization and optimization of e-beam evaporated optical coatings," in Optical Interference Coatings, OSA Technical Digest Series (Optical Society of America, 2001), paper ME8.