Data from a digital polarimeter?

1. Jul 9, 2008

LtStorm

Not sure if this is where this really belongs, as it's a question about equipment rather than actual chemistry, but, it's equipment that's usually used by chemists, so I figured I'd have the best chance of something being familiar with it here.

It's a simple question really; what does the data put out by a digital polarimeter look like? What form does it show it in? Brightness vs. Angle of Rotation, or does it have some way to tell directly what the specific rotation of the sample is without human interpretation?

I have an analogue polarimeter I'm trying to work with, but because the substance I was attempting to study seems to have a "wide" angle of rotation range, I was trying to quantify things better using a light sensor to read the changes in brightness. This seems to be working; with a blank/distilled water/nothing in the machine, I get what looks like a sine wave when graphing brightness vs. angle of rotation. With the blank its peaks and valleys are at 90, 180, 270, and 0/360, as I'd have expected.

Optically active samples appear to cause those peaks and valleys to offset. One highly rotated sample, a sucrose solution, I measured by eye as having a rotation of 56.2 degrees and when measured using the sensor it had the peaks and valleys of the graph offset by about that many degrees, i.e. the sensor read the light as being brightest at around 40 degrees rather than 90.

So I'm trying to figure out whether or not this is something digital polarimeters normally give as output data, or if I'm doing something different here.

2. Jul 17, 2008

Andy Resnick

The classic book is Azzam and Bashara, "Ellipsometry and Polarized Light" It has extensive discussions about polarimeters, how to reduce the data set to elements of the Stokes vector, and all kinds of other goodies. Can't beat it.