This is mostly a question for the physics types here. Though any input/ questions are welcome. It's rather a complicated question and experimental setup, I'll do my best. It's mostly a question about electric dipole transition selection rules.
So I'm doing Saturated Absorption Spectroscopy(SAS), also called Doppler free spectroscopy. You can google that, I looked at several web pages but didn't think any worth a link. The technique involves splitting a tunable laser beam in two and to send the two beams counter-propagating (in opposite directions but over lapped spatially) through a sample. (in this case Rb vapour) You monitor the transmission of the probe beam as the stronger pump beam saturates the atomic transitions. (In practice there is more than simple saturation going on... optical pumping type things happen too.)
I wanted to use the technique to show the Zeeman splitting of the atomic levels. I picked the 795 nm line and the Rb87 transition from F=2 to F'=1, (F is the total angular momentum of the ground state, F' refers to the excited state.) I then used circularly polarized pump and probe beams to further reduce the allowed transitions. With Right Hand Circularly (RHC) polarized light the change in the z-component of the angular momentum must be +1. (for LHC it's -1) Here's a diagram of the allowed transitions.
Here is a pic of the spectrum,
And with the SAS features,
And finally a pic with the background subtracted, and zoomed in on just the first two features.
Ok I then the pump beam RHC polarized to saturate the same transitions. And that didn't work! Turning up the B field first caused the SAS feature to flip over, and then a messy spectrum. I had to use LHC polarization on the pump beam to get a nice Zeeman spectrum. Here,
And that (after a lot of introduction) is my question. I'm missing a sign somewhere, that tells me the selection rules for light beams propagating in opposite directions.
I will observe that if you look at how things are spinning RHC going away from you and LHC coming towards you both have to polarization going in what you would call a clockwise direction.
Oh as a treat for reading this far here are three spectra, zoomed in with B=0, B= +10mT and B= -10mT,
Thanks George H.
Here's my whole dropbox folder