Raman-Ramsey CPT with a grating magneto-optical trap

We describe an experiment which combines cold ⁸⁷ Rb atoms from a grating magneto-optical trap (GMOT) with Lin±Lin coherent population trapping (CPT) and pulsed Ramsey interrogation. The bichromatic fields required for Lin±Lin are generated by combining light from a single external cavity diode laser (ECDL) with an electro-optic modulator (EOM) and an acousto-optic modulator (AOM). With this laser system and the GMOT, we are able to produce Raman-Ramsey fringes using either the F' = 1 or the F' = 2 excited states of the ⁸⁷Rb Di line. As a step towards realising a frequency standard based on the GMOT, we measure the Ramsey fringe amplitude as a function of the magnetic bias field and the excited state. We observe dark state interference with F^' = 1 and show that this interference is suppressed with F' = 2, as expected from prior work on CPT with ⁸⁷Rb in thermal vapour cells.