Tunable and injection-seeded operation of a narrow-linewidth BBO optical parametric oscillator pumped by 355 nm laser

A tunable, narrow spectral linewidth nanosecond pulsed BBO optical parametric oscillator (OPO) is demonstrated by pumping with a 355 nm ultraviolet (UV) laser derived from a Nd:YAG non-planar ring oscillator (NPRO) through multi-stage cascade amplification and frequency tripling. The narrow linewidth operation of the 355 nm pump source, combined with the singly-resonant ring cavity design, enables tunable operation and narrow linewidth signal output. By angle-tuning the BBO crystal, the OPO achieves a signal laser output from 470 nm to 517 nm, with an energy exceeding 19 mJ and a spectral linewidth below 0.07 nm across the tuning range. Single-frequency continuous-wave (CW) seed injection at a selected wavelength further enhanced performance, producing a stable, narrow-linewidth output aligned with the H-β Fraunhofer absorption line at 486.134 nm. At this central wavelength, the OPO delivers a maximum signal pulse energy of 23.8 mJ, a pulse width of 4.5 ns, and a pump-to-signal conversion efficiency of 40.7%. The spectral linewidth is significantly narrowed to 0.017 nm, with a measured wavelength stability of 11 MHz over a 30-minute period. These results highlight the laser system’s potential for high-precision applications requiring tunable, narrow-linewidth laser sources.