Coherent Dual-Frequency Emission of a Vertical External-Cavity Semiconductor Laser at the Cesium ${\rm D}_{2}$ Line

We describe the dual-frequency and dual-polarization emission of a diode-pumped vertical external-cavity semiconductor laser at 852 nm dedicated to the coherent population trapping of cesium atoms. The output power reaches ~20 mW on each frequency, with a frequency difference in the gigahertz range.