Highly Efficient Nanosecond 1.7 μm Fiber Gas Raman Laser by H2-Filled Hollow-Core Photonic Crystal Fibers

High-power and narrow-linewidth nanosecond pulsed intracavity crystalline Raman laser operating at 1.7 µm

We report on a high-power and narrow-linewidth nanosecond pulsed intracavity crystalline Raman laser at 1.7 µm. Driven by an acousto-optically Q-switched 1314 nm two-crystal Nd:YLF laser, the highly efficient cascaded YVO4 Raman laser at 1715nm was obtained within the well-designed L-shaped resonator. Thanks to the absence of spatial hole burning in the stimulated Raman scattering process, significant spectral purification of second-Stokes radiation was observed by incorporating a fused silica etalon in the high-Q fundamental cavity. Under the repetition rate of 4 kHz, the highest average output power for single longitudinal mode operation was up to 2.2 W with the aid of precision vibration isolation and precision temperature controlling, corresponding to the pulse duration of ∼2.8 ns and the spectral linewidth of ∼330 MHz. Further increasing the launched pump power, the second-Stokes laser tended toward be always multimode, and the maximum average output power amounted to 4.8 W with the peak power of ∼0.8 MW and the spectral linewidth of ∼0.08 nm. The second-Stokes emission was near diffraction limited with M2 < 1.4 across the whole pump power range.

Pulsed fiber laser oscillator at 1.7 µm by stimulated Raman scattering in H2-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 H₂. 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.

All-Fiber Gas Raman Laser by D2-Filled Hollow-Core Photonic Crystal Fibers

We report here an all-fiber structure tunable gas Raman laser based on deuterium-filled hollow-core photonic crystal fibers (HC-PCFs). An all-fiber gas cavity is fabricated by fusion splicing a 49 m high-pressure deuterium-filled HC-PCF with two solid-core single-mode fibers at both ends. When pumped with a pulsed fiber amplifier seeded by a tunable laser diode at 1.5 μm, Raman lasers ranging from 1643 nm to 1656 nm are generated. The maximum output power is ~1.2 W with a Raman conversion efficiency of ~45.6% inside the cavity. This work offers an alternative choice for all-fiber lasers operating at 1.6–1.7 μm band.

All-Fiber Tunable Pulsed 1.7 μm Fiber Lasers Based on Stimulated Raman Scattering of Hydrogen Molecules in Hollow-Core Fibers

Fiber lasers that operate at 1.7 μm have important applications in many fields, such as biological imaging, medical treatment, etc. Fiber gas Raman lasers (FGRLs) based on gas stimulated Raman scattering (SRS) in hollow-core photonic crystal fibers (HC-PCFs) provide an elegant way to realize efficient 1.7 μm fiber laser output. Here, we report the first all-fiber structure tunable pulsed 1.7 μm FGRLs by fusion splicing a hydrogen-filled HC-PCF with solid-core fibers. Pumping with a homemade tunable pulsed 1.5 μm fiber amplifier, efficient 1693~1705 nm Stokes waves are obtained by hydrogen molecules via SRS. The maximum average output Stokes power is 1.63 W with an inside optical-optical conversion efficiency of 58%. This work improves the compactness and stability of 1.7 μm FGRLs, which is of great significance to their applications.