16.8 GHz longitudinal mode spacing 486 nm blue laser for oceanic high-spectral-resolution lidar

A sub-nanosecond blue laser with a large longitudinal mode spacing at 486 nm was demonstrated based on a frequency-doubled potassium titanyl phosphate optical parametric oscillator. The pump laser was a 532 nm green laser with a pulse width of 0.76 ns at the maximum pulse energy of 4 mJ. With a cavity optical length of 8.9 mm, the output energy of 972 nm signal laser reached 0.8 mJ, corresponding to a conversion efficiency of 20%. The signal laser was frequency-doubled to a blue laser with a longitudinal mode spacing of 16.8 GHz, matching the frequency spacing of seawater Brillouin scattering signal peaks excited by 486 nm laser. The spectral linewidth, pulse width and single pulse energy of the blue laser were 0.28 nm, 0.57 ns, and 80 μJ, respectively. This blue laser provides a reliable laser source for verifying the feasibility of multi-longitudinal-mode laser technique in oceanic high-spectral-resolution lidar.