A robust phase-locked diode laser system for EIT experiments in cesium

We describe a phase-locked diode laser system specifically designed for experiments that require two stable frequency-offset locked wavelengths, here used to prepare coherence in atomic media. The system consists of two external-cavity diode lasers that are phase-locked using an ultra-low phase-noise digital-only phase detector and appropriate loop filters. The residual phase-noise variance sigma (phi) (2) was measured to be less than 0.02 rad(2). The system was used to demonstrate electromagnetically induced transparency (EIT) in Cs reaching a transmission of > 60% for a transparency window width of 1.1 MHz. We present a theoretical description of the measured transmission curves relying on the dephasing rate as the only free parameter.