Inhomogeneous/Interlayers Refinement

Inhomogeneous/Interlayers Refinement option allows you to perform a refinement of coating design with taking into account bulk inhomogeneity of coating layers and interface surface roughness. All types of targets (conventional targets, color targets, integral targets) can be used by this option. All opportunities provided by the Cone Angle and Line Width databases are also supported by the new refinement option.

Example: Design of chirp mirror working in the spectral range from 13 nm to 17 nm. Target reflectance is 7% and target GDD is 3000 \(as^2\). Substrate is Si, thin film materials are Si and Mo. It is known that in the EUV spectral range bulk inhomogeneity and surface roughness affects spectral characteristics significantly, so they must be taken into account in the design process. Also, due technological reasons, lower and upper limits of layer thicknesses are 1.5 nm and 6 nm.

chirp mirror EUV chirp mirror EUV
Interlayers of 1 nm thickness are specified. It is seen that they affect reflectance and GDD. Performance is worsened. In order to improve the performance, constrained optimization with interlayers was applied. After this optimization, both R and GDD performances improved: 
chirp mirror in EUV dispersive mirror EUV

See the details in:

  1. A. Tikhonravov, M. Trubetskov,  "Design of optical coatings taking into account thin film inhomogeneity," in Optical Interference Coatings, OSA Technical Digest (Optical Society of America, 2013), paper TD.6.
  2. H. Jiao, X. Cheng, G. Bao, J. Han, J. Zheng, Zh. Wang, M. K. Trubetskov, A. V.Tikhonravov, "Study of the HfO2/SiO2 dichroic laser mirrors having refractive index inhomogeneity," in Optical Interference Coatings, OSA Technical Digest (Optical Society of America, 2013), paper FB.5.