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Stress in optical thin films

In parallel to these studies of the optical and spectral properties of single- and multi-layer stacks, theoretical and experimental works have been performed on the effect of mechanical stresses in thin layers on the warpage induced effects of substrates.
Some first studies have allowed characterizing precisely the dependence of stress level on layer thickness for various classical materials.
In particular, we have demonstrated a non-linear dependence of stress on layer thickness.
This parametric study was carried by using Zernike decomposition of the flatness measurement of the warped coated substrates.
Additional work have also allowed identifying generic methods for the compensation of stress-induced deformation of coated substrates such as it is now able to control of flatness of coated samples with a precision of a few tens of nanometers and even to a few nanometers.
The combination of the control of stressed-induced deformation and the deposition of multilayers with high damage threshold have allow developing high performances mirrors that are being integrated within the laser delivery system and the laser beam circulator of the project ELI-NP.