Highly Efficient Sodium <i>D</i><sub>2</sub> Resonance Light Generation and Doppler-free Saturation Fluorescence Spectroscopy to Determine Reference Frequency for Sodium Lidar

The sodium D2 resonance light was generated in sum-frequency generation pumped with two continuous-wave distributed-feedback lasers. The output power reached 11 mW at a wavelength near the sodium D2 line with a high conversion efficiency in a fiber-coupled periodically poled LiNbO3 waveguide. Three dominant spectra, the D2-a, the D2-b, and the crossover resonance, were clearly observed in Doppler-free saturation spectroscopy by high-rate scanning the sum frequency at around the D2 resonance line with a linewidth of ≈ 3 MHz.