High-efficiency, 154  W CW, diode-pumped Raman fiber laser with brightness enhancement

Abstract

We demonstrate a high-power, high-efficiency Raman fiber laser pumped directly by laser diode modules at 978 nm. 154 W of CW power were obtained at a wavelength of 1023 nm with an optical to optical efficiency of 65%. A commercial graded-index (GRIN) core fiber acts as the Raman fiber in a power oscillator configuration, which includes spectral selection to prevent generation of the second Stokes. In addition, brightness enhancement of the pump beam by a factor of 8.4 is attained due to the Raman gain distribution profile in the GRIN fiber. To the best of our knowledge this is the highest power and highest efficiency Raman fiber laser demonstrated in any configuration allowing brightness enhancement (i.e., in either cladding-pumped configuration or with GRIN fibers, excluding step-index core pumped), regardless of pumping scheme (i.e., either diode pumped or fiber laser pumped).

High-brightness all-fiber Raman lasers directly pumped by multimode laser diodes

“…[5] with a focus on the opportunities of high-quality beam generation using fiber Bragg gratings (FBGs) as cavity mirrors [7][8][9][10] , whereas second one aims at high-power capabilities based on freespace pump coupling and bulk mirrors cavity [4,11,12] . In the last case, up to 154 W power is obtained at ∼1020 nm [12] , but Raman output at this wavelength is not as interesting, because higher power and narrower linewidth are available from YDFLs [13,14] . In addition, in spite of significant improvement of the output beam quality (M 2 = 4-8) in comparison with that for the pump beam (M 2 ∼ 20) due to the Raman clean-up effect in GRIN fibers, it is far from singlemode regime.…”

Greater than 2 kW all-passive fiber Raman amplifier with good beam quality

“…Yao et al proposed an LD-pumped RFL in 2015, obtaining a 20 W laser from GRIN fiber with an M 2 that was improved from 22 to 5, and a BE of 5.2 [27] . In 2016, Glick et al reported an LDpumped RFL based on GRIN fiber [28] , and the maximum power output reached 154 W with an M 2 of 8 and a BE of 3 through optimizing the fiber length [29] . Zlobina et al also studied RFL based on GRIN fiber, and the beam quality was quite good with an M 2 of~1.2 and a BE of~40, and the demonstrated power was 10 W [18] .…”

Pure Passive Fiber Enabled Highly Efficient Raman Fiber Amplifier With Record Kilowatt Power

“…Then higher power output is acquired through fiber lasers employing integrated Yb-Raman gain [12][13][14], nevertheless the brightness decreases in the Raman shifting process and the issues of PD reappear which will influence the performance of laser system. Recently the fast development of fiber components and the brightness enhancement of pump lasers make it possible for power scaling in passive fibers that employ pure Raman gain [15][16][17][18][19][20][21][22]. For instance, using graded-index (GRIN) fiber in core-pumped structure has a relatively simple construction and enhances the brightness in fiber core.…”

“…In 2016, Y. Glick et al report an LD-pumped Raman fiber laser in free space configuration which obtain 80 W Raman laser output, and brightness enhancement is achieved through the beam clean-up procedure of GRIN fiber in the cavity [18]. Then by means of modifying the system and adding up pump energy the lasing power increases to 154 W [19]. In 2017, A. Zlobina et al propose an all-fiber Raman fiber laser that also utilizes GRIN fiber and acquire power of 50 W at 954 nm, while the FBGs inscribed in GRIN fiber are the key devices which are specially fabricated for efficient reflection and mode selection effect [20].…”