Stabilization of frequency-doubled synchronously pumped optical parametric oscillators using an optimized parasitic wavelength

We present a systematic study on cavity-length stabilization in frequency-doubled synchronously pumped optical parametric oscillators (SP-OPOs) utilizing parasitic optical pulses. Through an analysis of the correlation between the characteristics of parasitic light and the effectiveness of stabilization, we have determined that the response slope of parasitic light to cavity detuning is the key determinant of stabilization efficacy, independent of its nonlinear frequency-conversion origin. To overcome practical challenges in wavelength selection, we have developed a nonlinear envelope equation (NEE) simulation method that incorporates group-velocity dispersion, self-phase modulation, and <i>χ</i>⁽²⁾ interactions to model spectral features and response slopes near the SP-OPO oscillation peak accurately. Experimental validation conducted on a 31.3-μm-period periodically poled lithium niobate (PPLN) SP-OPO demonstrates good agreement with simulated results. Notably, the 656 nm <i>p</i> + <i>s</i> parasitic component, characterized by the most pronounced response slope, exhibits superior locking performance with an integrated relative intensity noise (RIN) of 0.025% (10 Hz to 50 kHz) for the frequency-doubled output. This represents an 8.4-fold reduction compared to the 648 nm component (0.21% integrated RIN), while maintaining 0.13% RMS power stability over one hour. Our methodology facilitates optimized stabilization and is adaptable to multi-period PPLN systems for the development of broadly tunable short-wavelength laser sources, thereby advancing applications in precision atomic spectroscopy and quantum optics.