Material correction factors

Not only layer refractive indices but also layer thicknesses may exhibit variations after the exposition to air. The ratio of layer thicknesses in air and vacuum is called correction factor. Correction factors are different for different layer materials and are dependent on the type of deposition process and many other factors. We recommend performing preliminary comparative investigation of single layer parameters in vacuum and air in order to check whether layer thicknesses are stable after the exposition to air or non-unit correction factors should be introduced for the some layer materials. OptiChar characterization software is especially well suited for such investigation.

Correction factors can be also used in the case of indirect spectral photometric monitoring when photometric measurements are done for a witness sample while manufactured samples are located in other positions inside the chamber as compared to this sample. In this case correction factors represent the ratios of layer thicknesses of manufactured samples to the corresponding layer thicknesses of witness sample.

If indirect optical monitoring is used and layer thicknesses also exhibit variations after the exposition to air, then correction factors should take into account both factors.

References:

1. A. V. Tikhonravov, M. K. Trubetskov, Online characterization and reoptimization of optical coatings, Proc. SPIE. 5250, Advances in Optical Thin Films 406 (2004)
2. 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).
3. 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.
4. 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.