Abstract
We describe novel fiber Raman lasers pumped directly by spectrally combined high power multimode laser diodes at ~975 nm and emitting at ~1019 nm. With a commercial multimode graded-index fiber, we reached 20 W of laser output power with a record slope efficiency of 80%. With an in-house double-clad fiber, the beam quality improved to M2 = 1.9, albeit with lower output power and slope efficiency due to higher fiber loss. We believe this is the first publication of a fiber Raman laser cladding-pumped directly by diodes.
Highlights
Fiber lasers have become leading candidates in the high power regime thanks to advantages over traditional solid-state lasers such as gain efficiency, compactness, ruggedness, and flexibility
Ytterbium-doped fiber (YDF) lasers emitting around 1 μm work well, and have reached 20 kW of output power with excellent beam quality [2]
While fiber Raman lasers (FRLs) pumped by MM diodes have been demonstrated recently at wavelengths as short as 0.8 μm [13], the high fiber loss meant that the required pump brightness could only be reached in pulsed mode, which restricted the average power
Summary
Fiber lasers have become leading candidates in the high power regime thanks to advantages over traditional solid-state lasers such as gain efficiency, compactness, ruggedness, and flexibility. This includes wavelengths not covered by alternative practical pump sources, e.g., in the 800–1000 nm range Despite these attractions, power-scaling of diode-pumped FRLs has been held back by the high pump densities and low fiber propagation losses that are needed to reach laser threshold, since stimulated. While FRLs pumped by MM diodes have been demonstrated recently at wavelengths as short as 0.8 μm [13], the high fiber loss meant that the required pump brightness could only be reached in pulsed mode, which restricted the average power. For power-scaling of FRLs, lower fiber loss and superior cw brightness and power make 0.9–1 μm diodes a better choice, and devices based on MM pumping of MM fibers have recently been demonstrated [14] These still operated relatively close to threshold, with output power of 3 W and slope efficiency of 35% or less. We estimate the improvements possible with optimized and lower-loss laser configurations, as well as with improved Raman gain fibers and pump sources
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