On-line re-optimization

• The main goal of the on-line re-optimization is the compensation for errors in thicknesses of already deposited layers. On-line re-optimization is done on the basis of the on-line characterization results. Thus high accuracy and reliability of these results is essential for the success of the on-line re-optimization.
• The OptiReOpt re-optimization routine corrects theoretical thicknesses of those design layers that haven’t been deposited yet. This correction is done with respect to the theoretical targets used for coating design so as to provide the best possible fit of theoretical targets by spectral characteristics of re-optimized design.
• If for some reason theoretical design targets are not available, then the correction is done with respect to the spectral transmittance/reflectance calculated for the initial theoretical design.
• The OptiReOpt re-optimization routine is extremely efficient from the computational point of view and does not require interrupting the deposition process in order to wait for the corrected theoretical design.

On-line re-optimization is only sensible if we have reliable on-line characterization results.

A reliable on-line characterization is much more computationally extensive than the on-line re-optimization, especially when the number of deposited layers is high. OptiReOpt provides extremely efficient optimization routines allowing to prevent interruptions of a deposition process caused by the delays of characterization results.

• On-line re-optimization is a refinement procedure;
• On-line re-optimization is activated only if the registered error exceeds specified threshold level;
• On-line re-optimization is not performed if it results in a small decrease of the merit function;
• It is worthwhile to skip on-line re-optimization in the case when the last deposited layer is a low-index layer. If necessary, the online re-optimization can be done one step later, after the deposition of the next high index layer.

Combination of broadband optical monitoring with OptiReOpt on-line characterization and subsequent on-line re-optimization has proven to be an efficient technique for production of complex optical multilayer coatings. See details here:

• S. Waldner, M. Padrun, Assessing the Suitability of Coating Designs for In-Process Reoptimization, Optical Interference Coatings Technical Digest,  2013, WB.7
• http://www.dynavac.com/systems/thin-film-systems/precision-optical-coating-systems/spectrum-pro-optical-monitoring-system/
• https://www.photonics.com \Article.aspx?AID=52257

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.