Enhanced frequency tuning and suppressed <100 Hz relative intensity noise of A 3.4 W 770 nm all-PM fiber laser

In this work, we propose and demonstrate, for the first time, a high-power, narrow-linewidth, all-polarization-maintaining (PM) fiber laser operating at 770 nm featuring enhanced wavelength detuning capability and broadband linewidth tunability, which is expected for enhancing the measurement sensitivity of spin-exchange relaxation-free (SERF)-based atomic sensors. The 770 nm laser is realized via second-harmonic generation (SHG) in a periodically poled lithium niobate (PPLN) waveguide, delivering a maximum output power of 3.4 W, which represents the state-of-the-art power level among all-PM fiber lasers at this wavelength. The laser linewidth can be continuously tuned from 2.9 kHz to 123 GHz while sustaining an output power above 2.4 W. By adjusting the phase-matching temperature of the SHG process, a maximum wavelength detuning of ±40 GHz is achieved, further extending the overall linewidth tuning range to 148 GHz with a maintained output power exceeding 2.0 W. We eliminate parasitic 513 nm green light and adopt a two-stage polarization beam splitter combined with half-wave plates at the laser output, suppressing the 770 nm laser’s relative intensity noise (RIN) to state-of-the-art values: below −80 dBc/Hz @0.3–2 Hz, −100 to −110 dBc/Hz @2–10 Hz, and approximately −115 dBc/Hz@10–100 Hz.