The signal field was generated by a 780 nm external cavity diode laser (ECDL, MOGLabs CEL), which was blue detuned from the $5S_{1/2}(F'=2)$ feature. The control field was generated by a 776 nm ECDL (MOGLabs CEL) and was intensity modulated by an electro-optic modulator (Exail NIR-MPX800), and then amplified (MOGLabs MOAL) to produce a square control pulse of approximately 25 mW peak power and down to 42 ns pulse duration. Each laser was frequency stabilized using a scanning transfer cavity. The relative position of the signal and control field resonances are measured and then an error signal was generated from a RedPitaya locking system. The cavity consists of two beamsplitters and two mirrors, with an atomic vapor cell placed inside. The atomic medium is isotropically enriched rubidium-87 vapor, and is placed inside the ring cavity. The vapor is contained within a 5 cm glass cell with anti-reflection coatings, heated to approximately 60$^\circ$C to increase the optical depth whilst minimizing atomic absorption. A lens inside the cavity focuses the signal and control to the centre of the atomic vapor cell. The signal and control light is coupled into the fundamental transverse cavity mode, such that sharp resonances are seen on an oscilloscope. When the control field is applied, the signal field undergoes a phase shift, and is switched from the transmitted to reflected port. The reflected signal travels back on the control arm of the experiment and is detected after a circulator, and the transmitted light exits the cavity on the second port and is detected in free-space.