Defining and Evaluating Multilayer Coatings in FRED Marko Swoboda

What are Multilayer Coatings? Anti-Reflection Coatings consist of one or more layers Dielectric Mirrors use constructive/destructive interference interferometric filters select narrow lines by clever layer sequence required:  precise control of optical layer thickness  homogeneous deposition of dielectric/optical media

Examples of Coatings Distributed Bragg-Reflector:Narrow-band Interferometric Filter:   

What is their role in FRED? most raytraced objects act by their refractive indices, a coating is only a few micron thick  still major influence multilayer coatings act on the phase of the light, in reflection and transmission and achieve the highest possible reflectivities for single wavelengths all that makes it important to include such coatings in exact simulations of any system

How to make a coating? simple as that: two ways: -by clicking and typing -by script and data (also typing)

Coatings by Clicking tons of options:  focus on the most general: Thin Film Layered Coatings

Coatings by Clicking layers can be repeated in groups (e.g. lambda/4 stacks)

Coatings by Clicking 3-pair DBR don’t forget to include the materials into your database from the standard or self-defined materials!  later

Plotting Coating Properties once defined, coatings can be added to any surface in FRED their properties are evaluated with the plot function

Plot Function Options great number of settings wavelength region always the maximum of present rays polarization sensitive amplitude AND phase of reflected light

Plot Function Results: 3-pair DBR plot function 0 degree incidence saveable as text file

Other Option for Coating Definition write a script, defining the properties:

Evaluation still has to be done by hand... click on plot coating  the filter just defined narrowband transmission peak!

One more example: DBR with high-index layer on top: reflectance

One more example: DBR with high-index layer on top: phase phase jump at design wavelength!

One more example: solution: low-index-layer on top: phase-jump only in transmitted light!

Finally: New Materials Thin-Film layers so far are only limited by the availability of materials in the FRED-database defining a new material from external parameters helps:

Best way: Scripts generated by Matlab get lambda, n, k values from CXRO or your favourite website

Conclusion Coatings can greatly alter the behaviour of any surface in FRED they are defined a bit on the side, and can be evaluated independently from rays (mostly) they are defined from either standard materials in the optical region or from imported data (preferably with matlab) for any other wavelength region