[NormalPolymer]

Hi, all:

I'm using a UV-vis spectroscope (Lambda-900, PerkinElmer) for a transmission measurement. I autozero the baseline from 300 to 700 nm using two parallel polarizers, and then set wavelength=0 nm so that the probing light is white light. By rotating the second polarizer, I should be able to get maximum when two polarizers are parallel and minimum when two are perpendicular. Now I have a problem: I got a negative transmission value when two polarizers are perpendicular.
What could cause a negative T value, and what can I do to solve this problem?
Thank you all!