Measuring optical properties at temperature

[rnewstrom]

I am working on a project where I need to measure optical properties on a plastic disc at high and low temperature. The disc is supposed to be flat.

One of our techs used two polarizing lenses, cross polarized and sandwiching the disc. This revealed a light/dark pattern that changes as the disc cools off from high temperature.

However, we are not entirely sure what this signifies. For one there is a cross pattern related to orientation of the filters (it doesn't change orientation when the disc is rotated). But the pattern definitely changes as the disc cools from high temperature, so it doesn't appear to be just an effect of the filters.

I have two questions:
1. Does anyone know, or know where I can find information on, what the patterns signify?

2. Is there a better way to measure what is going on? I was thinking of using some oil to get thin film measurements, which would at least tell me about the surface deformations...

Thanks!

 

[IRstuff]

All that signifies is that the plastic's polarization orientation is changing as a function of temperature. If you want to check flatness, then check for flatness. You should then be looking for either optical flats, checking for changes in the fringe pattern, or an interferometer, checking the same.

Another possibility, if the flatness change is large, is to use a laser profilometer, which will directly compute the surface variations.

TTFN

FAQ731-376

 

[DanStro]

What specific properties are you trying to measure?