Wavelength switchable potassium Faraday laser.

A laser with a switchable wavelength between 770 nm and 767 nm, corresponding to the potassium D1 and D2 lines, is a promising tool for manipulating potassium atoms. Here, we develop a potassium Faraday laser using a potassium atom-based Faraday anomalous dispersion optical filter (FADOF) as its frequency selection element. By dynamically adjusting the central frequency of the peak transmission across the entire transmitted spectrum of the potassium FADOF, the laser can operate either in single mode at either 770 nm or 767 nm, or emit both simultaneously. In single-mode operation, the laser wavelength remains aligned with the atomic transitions, exhibiting a narrow linewidth of 14.96 kHz at 770 nm and 13.07 kHz at 767 nm. In dual-mode operation, both modes are sustained continuously, with frequency drifts of less than 0.3 GHz for 200 minutes. Furthermore, we perform modulation transfer spectroscopy (MTS) and stabilize the laser to the 39K 4S1/2F = (1, 2) → 4P1/2F' = 2 and 4S1/2F = (1, 2) → 4P3/2F' transitions. The corresponding frequency stability, measured by the optical heterodyne beat note between two identical systems, is 1.57 × 10-12 and 8.77 × 10-13 at 1 s, respectively. This architecture introduces a novel approach to the generation of wide-range wavelength switching within a single laser. In addition, with its narrow linewidth and impressive frequency stability, it serves as a reliable source for ultracold atom physics and quantum precision measurement.