Interference in thin films: why thin?

[yoran]

Hi,

When you have interference in thin films, why does the film has to be thin? Why doesn't it work with "thick" films? In my textbook they don't explain this constraint...

Thank you.

 

[Andy Resnick]

Interference can indeed work with thick films (or large cavities). Thin films are used in real devices because they are easier to make- most antireflection coatings consist of many, many layers of materials. And manufacturing errors are more forgiving for thin film interference rather than thick film interference.

I think there is a difference in polarization, tho- there, thin films/objects give better performance (zero-order retarders, for example) than higher order devices.

 

[yoran]

Ok thank you. So it's more based on practical reasons than theoretical ones.