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 results @ 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

narrowbandtransmissionpeak!

One more example:

• DBR with high-index layer on top: reflectance

One more example:

• DBR with high-index layer on top: phase

phasejump atdesignwavelength!

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