Narrow-linewidth megahertz-repetition-rate optical parametric oscillator for high-speed flow and combustion diagnostics

摘要

We demonstrate the ability to generate ultra-high-frequency sequences of broadly wavelength-tunable, high-intensity laser pulses using a custom-built optical parametric oscillator pumped by the thirdharmonic output of a u22burst-modeu22 Nd:YAG laser. Burst sequences consisting of 6-10 pulses separated in time by 6-10 Îs are obtained, with average total conversion efficiency from the 355 nm pump to the near-IR signal and idler wavelengths of 33%. Typical individual pulse output energy for the signal and idler beams is in the range of 4-6 mJ, limited by the available pump energy. Line narrowing is demonstrated by means of injection seeding the idler wave using a low-power external-cavity diode laser at 827 nm. It is shown that seeding reduces the time-averaged linewidth of both the signal and idler outputs to 300 MHz, which is near the 220 MHz Fourier transform limit. Line narrowing is achieved without recourse to active cavity stabilization.