Speaker
Description
The TUCAN collaboration aims to provide a world-class measurement of the neutron EDM, with an eventual precision goal of $1\times10^{-27}\ e\cdot$cm. In order to achieve this target sensitivity the magnetic environment in the experimental region must be very carefully controlled and monitored. To this end TUCAN has developed a suite of Cs based optically pumped magnetometers with the primary purpose of magnetic field mapping, i.e. gradient determination up to third order in a spherical harmonic decomposition. These sensors operate by probing the D2 line in Cs with linearly polarized light. Optical pumping leads to the production of an aligned atomic state. Probing this state with resonant light leads to an optical rotation of the probing light, the time dependence of which gives a measurement of the Larmor frequency of the atomic ensemble, and therefore a measurement of the external magnetic field experienced by the Cs atoms. These sensors have been shown to have a probe laser frequency and power dependent measurement offset, which we call a light shift.
I present the theoretic basis for the shift, as well as the measurement technique developed to directly measure the light shift in-situ, which involves allowing the Cs atomic ensemble to precess in the absence of any pumping or probing light, a so-called precession-in-the-dark measurement. By observing the relative phase shift during the dark period, the true in-the-dark precession frequency can be found, which is nominally precisely the Larmor frequency and therefore a good measurement of the magnetic field. Preliminary measurements on the sensor with the most pronounced light shift show a shift of 154(5) pT at an optimal operating probe power of 7 uW.