研究目的
Investigating the cascaded Raman generation of the 2nd Stokes order in a 1.1-km long graded-index fiber (GIF) with 100-μm core directly pumped by 915-nm diodes, focusing on beam quality improvement and efficiency.
研究成果
The study demonstrates high-power (27 W) 2nd-order random lasing at 996 nm in an all-fiber scheme with high slope efficiency (~70%) and nearly diffraction limited output beam (M2 ≈ 1.6). The random generation in multimode GIF is more efficient and provides higher beam quality than conventional RFL schemes. The developed laser combines beam clean-up at Raman conversion, low-order transverse mode selection by special FBGs, and the influence of Rayleigh backscattering, offering a high-brightness laser source for various applications.
研究不足
The study is limited by the maximum pump power available and the threshold for the next Stokes order generation. The beam quality and efficiency are also dependent on the specific configurations of the FBGs and the Raman gain profile.
1：Experimental Design and Method Selection:
The study utilizes an all-fiber scheme for cascaded Raman generation in a 1.1-km long GIF with 100-μm core, directly pumped by 915-nm diodes. The 1st Stokes order is generated in a linear cavity formed by two fiber Bragg gratings (FBGs), and the 2nd Stokes wave is generated in either a linear or half-open cavity with random distributed feedback via Rayleigh backscattering.
2：1-km long GIF with 100-μm core, directly pumped by 915-nm diodes. The 1st Stokes order is generated in a linear cavity formed by two fiber Bragg gratings (FBGs), and the 2nd Stokes wave is generated in either a linear or half-open cavity with random distributed feedback via Rayleigh backscattering.
Sample Selection and Data Sources:
2. Sample Selection and Data Sources: The GIF used has a 100-μm core and is 1.1-km long. Pump radiation is from three fiber pigtailed high-power LDs operating at 915 nm.
3：1-km long. Pump radiation is from three fiber pigtailed high-power LDs operating at 915 nm.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: High-power LDs, multimode fiber pump combiner, FBGs, dichroic mirrors, bandpass filters, power meters, optical spectrum analyzer, Thorlabs M2-measurement system.
4：Experimental Procedures and Operational Workflow:
Pump radiation is combined and coupled into the GIF. The 1st Stokes wave is generated in a linear cavity formed by FBGs, and the 2nd Stokes wave is generated in either a linear or half-open cavity. Output power, spectrum, and beam quality are measured.
5：Data Analysis Methods:
Output power and spectrum are measured directly. Beam quality parameter M2 is measured using the Thorlabs M2-measurement system.
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