Thin Film Evaporation - Anti-reflective coating

[bnay]

Hello there,

Right now I'm in a physics lab in which I have a vacuum jar, a thin film evaporation apparatus, and the instructions to do something interesting. I'm looking at a bunch of ideas right now, but one project that appeals to me is a multi-layer anti-reflective coating. The way I'd like to do it is to create an index gradient between air (n~1) and glass (n~1.5) at index intervals of approximately 0.1. I've found several materials I can use for n=1.3 and 1.4, but when it comes to 1.1 and 1.2 I'm beginning to doubt there are any that I could readily acquire.

Anyways, my question is, are there any solid materials that I could evaporate onto a glass substrate with an index of refraction between 1 and 1.3? If not, is there another way to make a multi-layer anti-reflective coating (I have 8 lab periods and need to be able to write a fairly large report on this, so the single layer of Magnesium Fluoride I've made is a bit too simplistic for that), or should I just move on to high reflective coatings or wave plates?

 

[Gokul43201]

I've found several materials I can use for n=1.3 and 1.4, but when it comes to 1.1 and 1.2 I'm beginning to doubt there are any that I could readily acquire.

Your doubt is not misplaced.

Anyways, my question is, are there any solid materials that I could evaporate onto a glass substrate with an index of refraction between 1 and 1.3?

There are some polymers near 1.3, but not anything I'm aware of that's lower.

If not, is there another way to make a multi-layer anti-reflective coating (I have 8 lab periods and need to be able to write a fairly large report on this, so the single layer of Magnesium Fluoride I've made is a bit too simplistic for that), or should I just move on to high reflective coatings or wave plates?

You could probably make a multi-layer coating with MgF2 and a suitable, high-index glass, but you'll have something with a narrow bandwidth. So, if you're going to engineer such a device, you should start your design based on the wavelength of the laser that you'll be using for the demonstration.

Incidentally, have you measured your MgF2 film to see what the thickness variation or roughness looks like?

 

[RocketSci5KN]

http://www.aip.org/tip/INPHFA/vol-10/iss-5/p26.html [Broken]

Aerogels appear to fit the bill, but I can't see any way to coat them onto a substrate as a very thin film...