Hi there, Having a bit of trouble working something out for a lab experiment at uni - not sure if this really counts as a 'homework' question - but if it does, moderators, feel free to move it there! So we've got linearly polarised laser light hitting a quarter waveplate to create circularly polarised light, where the incident laser light is incident at 45 degrees to one of the fast/slow axes on the waveplate. Then this circular light is going through a linear polariser before hitting a photodiode, connected to what is basically a voltmeter. A quick note about the linear polariser - we have that there to ensure the quarter waveplate is set up correctly - the linear polariser is crossed with the laser so that, on their own, nothing gets through to the photodiode. To ensure the quarter waveplate was set up correctly to create circular light, we rotated the quarter waveplate until no light was being picked up by the diode, noting that angle, and then rotating it again through 90 degrees so that nothing was being picked up by the photodiode again (the scale on the waveplate is arbitrary as it'd been cleaned and the dial had just been put back in some random position), so that halfway between the two angles (on the scale) gave the 45 degrees needed to create circularly polarised light. (is this right??) So, here's the problem: how do we use this set up to measure the voltages for the left handed and right handed circular components of the circular polarised light. The main problem here really is that we're not sure what's going on in between the linear polariser and the photodiode. Sorry if this all sounds rreally confused - I definitely am!