Multi-frequency Doppler-free spectroscopy of cesium using an external cavity diode laser

We employed a different approach to develop multi-frequency saturated-absorption spectroscopy (SAS) involving both cesium hyperfine ground state levels using a multimode external cavity diode laser (ECDL), which could operate with neither another independent laser nor a modulator. The multi-frequency SAS is formed by atomic velocity groups on resonance with both of the laser modes from an ECDL in multimode operation, which are counterpropagated through the vapor cell as a quasicoherent pair of laser beams. A sign reversal of the subDoppler resonance under special pump-probe polarization with and without applied magnetic fields is observed. Simultaneously, the optical microwave generation of the multimode ECDL is also investigated experimentally. The free-running linewidth of the beat note spectra between two modes is about 475 Hz, which indicates a high coherence between them. This oscillator- and modulator-free approach provides a complementary scheme for existing optical microwave generation and has potential for improvements. & COPY; 2023 Optica Publishing Group