generation of ripples or harmonics in the interface of the coating.
According to Ogurtani's irreversible thermodynamic theory of surfaces and interfaces, the uni- and bi-axial surface compressive stresses induced and/or enhanced surface roughness even they trigger crack formation and propagation. On the other hand uni and bi-axial tension stresses inhibit surface roughness and ripples .
In your case may be due the lattice miss- match or thermal expansion coefficient differences between matrix and the coating material some compressive stresses are generated at the interface because of which you have this problems.
Conventional theory of Asoro-Tiller theory can't explain the effects of the sign difference between tension and compression on the surface stability because it uses only the strain energy density, which is all ways positive quantity. Best regards
Note: In the case of grain boundary grooving just the opposite effect occurs when you apply uniaxial tension then the thermal grooving shows acceleration and finally ends up with the crack initiation at the groove tip causing premature GB fracture. But uni or bi-axial axial compressive stops thermal grooving! rather produces surface ridges around GB regions as observed experimentally.
I am not sure to understand the question. If the ripples, sidelobes and harmonics that you describe are seen in the optical spectrum of the multilayer (reflectance, transmittance; where this terminology is often used), than I suggest to try to make a rugate (graded index) filter to remove the harmonics, with an apodization envelop to remove the ripples (Kaiser function is efficient for that).
yes sir, the sidelobes or ripples can be reduced by using graded index rugate coatings. but for fabrication of these types of filters its a challenging task. in this filter fabrication what and all necessary precautions should we need to take.
please explain it clearly sir.
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