A 780 nm Dual-Frequency Faraday Laser

We demonstrate a dual-frequency (DF) Faraday laser operating on 780 nm using an ⁸⁷Rb Faraday anomalous dispersion optical filter (FADOF) as the frequency selection element. The frequencies of the two modes correspond to the transition of ⁸⁷Rb 5²S1/2 (F=1) to 5²P3/2 and 5²S1/2 (F=2) to 5²P3/2, respectively. The output laser wavelength has good robustness to the laser diode’s current and temperature fluctuations. The frequency difference between the two modes is tunable with the temperature of ⁸⁷Rb vapor cell and cavity length. Besides, the two modes share good coherence with the most probable linewidth of the beat-note spectra being 3 kHz. Such a 780 nm DF Faraday laser can be used in precision measurement, such as, laser frequency stabilization, optical microwave generation, and coherent population trapping (CPT) atomic clocks.