1-Watt, sub-kilohertz-linewidth 1123 nm MOPA laser based on an NPRO seed

We present a low-noise 1123 nm laser based on a master oscillator power amplifier (MOPA) configuration. A specially coated Nd:YAG nonplanar ring oscillator (NPRO) is employed as the seed, generating single-frequency radiation at 1123 nm with low intensity and frequency noise. Two cascaded ytterbium-doped fiber amplifiers (YDFA) boost the output power to 1 W while preserving the seed's spectral purity. The combined solution of NPRO and MOPA can ensure high output power while maintaining low noise. In free-running operation the laser achieves a sub-kilohertz linewidth (834 ± 63 Hz), a signal-to-noise ratio (SNR) exceeding 50 dB, and excellent power stability (<0.5% over 4000 s). Relative intensity noise (RIN) reaches 1×10^-2 Hz^-1/2 at 1 mHz, and frequency noise is 7.9×10⁴ Hz/Hz^1/2 at 1 Hz.