Narrow-Linewidth Megahertz-Repetition-Rate Optical Parametric Oscillator for High-Speed Flow and Combustion Diagnostics

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 third harmonic output of a "burst-mode" Nd:YAG laser. Burst sequences consisting of 6-10 pulses separated in time by 6-10 microsecond are obtained, with average total conversion efficiency from the 355 nm pump to the near-IR signal and idler wavelengths of approx. 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 approx 300 MHz, which is near the 220 MHz Fourier transform limit. Line narrowing is achieved without recourse to active cavity stabilization.
Sponsored in part by the National Science Foundation, Division of Chemical and Transport Systems. Prepared in collaboration with Innovative Scientific Solutions, Inc., Dayton, OH; the Department of Mechanical Engineering, Iowa State University, Ames, IA; and the Propulsion Directorate, Air Force Research Laboratory, Wright-Patterson AFB, OH. Published in Applied Optics, v47 n1 p64-71, 1 Jan 2008.