Abstract
Abstract We report a 2 kW all-fiberized Raman fiber amplifier with efficient brightness enhancement based on the graded-index fiber. The maximum power output reaches up to 2.034 kW centered at 1130 nm, with a conversion efficiency of 79.35% with respect to the injected pump power. To the best of our knowledge, this is the highest conversion efficiency obtained for any Raman laser system using graded-index fiber. An optimized fiber combiner adopting graded-index fiber as the pigtail fiber was fabricated, enabling the preservation of the seeding brightness in the core-pumped Raman fiber amplifier, and further enhancing the ultimate brightness of the output laser after amplification. At the maximum power output, the beam quality parameter M2 is 2.8, corresponding to a signal-to-pump brightness enhancement factor of 11.2. As far as we know, we obtain the highest brightness enhancement among Raman fiber lasers of over 100 W, and the best beam quality for graded-index Raman fiber lasers of over 150 W.
Highlights
The fiber laser has undergone rapid development, with outstanding properties in terms of power output, brightness and optical efficiency[1, 2]
We demonstrated an Raman fiber amplifier (RFA) with an optimized input seed beam quality M2 of 3.37, which is ~4.7 times higher than that in previous work[20]
The power output of the amplifier as a function of the launched pump power is shown in Figure 2, and the total power output rises almost linearly with increasing pump laser power
Summary
The fiber laser has undergone rapid development, with outstanding properties in terms of power output, brightness and optical efficiency[1, 2]. At the time of writing, the most common implementation is based on active fibers such as Yb-doped fiber, boosting the record for power scaling to greater than 10 kW[3,4,5]. Another way to obtain high-power laser output is the Raman fiber laser (RFL), which employs the stimulated Raman scattering (SRS) effect in a piece of passive fiber without any rare-earth dopants[6,7,8]. It can emit across almost the whole spectrum of transparency of a silica window, in particular beyond the emission band of rare-earth-doped fiber lasers[9,10,11,12,13,14,15,16,17,18,19]
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