Pulsed fiber laser oscillator at 1.7 µm by stimulated Raman scattering in H-filled hollow-core photonic crystal fibers.

We have reported a pulsed fiber gas Raman laser oscillator at 1.7 µm based on an all-fiber resonant cavity, which is made by splicing solid-core fibers with a 50-meter-long hydrogen-filled hollow-core photonic crystal fiber and further introducing homemade fiber Bragg gratings at the Raman wavelength. Pumping by a homemade pulsed 1540 nm fiber amplifier, a 1693 nm Stokes wave is obtained by pure rotational stimulated Raman scattering of H. The maximum optical-to-optical efficiency inside the hollow-core fiber is about 54% with the repetition frequency of 6 MHz, giving an average Raman power of 1.5 W, and the Raman threshold of peak power is as low as 3.6 W, which is more than 10 times lower than that of the single-pass structure. The relationship between pulse characteristics and Raman threshold is systematically studied, and the Raman threshold can be reduced dramatically when the repetition frequency of pulses is consistent with the resonant frequency of the cavity. This work provides good guidance for achieving low-threshold pulsed all-fiber gas Raman lasers, which is significant for development and application.