Evmenova Ekaterina A, Kuznetsov Alexey G, Nemov Ilya N, Wolf Alexey A, Dostovalov Alexandr V, Kablukov Sergey I, Babin Sergey A
Institute of Automation and Electrometry SB RAS, Novosibirsk, 630090, Russia.
Novosibirsk State University, Novosibirsk, 630090, Russia.
Sci Rep. 2018 Nov 30;8(1):17495. doi: 10.1038/s41598-018-35767-9.
Raman lasing in a graded-index fiber (GIF) attracts now great deal of attention due to the opportunity to convert high-power multimode laser diode radiation into the Stokes wave with beam quality improvement based on the Raman clean-up effect. Here we report on the cascaded Raman generation of the 2nd Stokes order in the 1.1-km long GIF with 100-μm core directly pumped by 915-nm diodes. In the studied all-fiber scheme, the 1st Stokes order is generated at 950-954 nm in a linear cavity formed at GIF ends by two fiber Bragg gratings (FBGs) securing beam quality improvement from M ≈ 30 to M ≈ 2.3 due to special transverse structure of FBGs. The 2nd Stokes wave is generated either in linear (two FBGs) or half-open (one FBG) cavity with random distributed feedback via Rayleigh backscattering. Their comparison shows that the random lasing provides better beam quality and higher slope efficiency. Nearly diffraction limited beam (M ≈ 1.6) with power up to 27 W at maximum gain (996 nm), and 17 W at the detuned wavelength of 978 nm has been obtained, thus demonstrating that the 2-order random lasing in diode-pumped GIF with FBGs provides high-efficiency high-quality beam generation in a broad wavelength range within the Raman gain spectral profile.
由于基于拉曼净化效应有机会将高功率多模激光二极管辐射转换为具有改善光束质量的斯托克斯波，渐变折射率光纤（GIF）中的拉曼激光如今备受关注。在此，我们报告了在一根1.1千米长、纤芯为100微米的GIF中，由915纳米二极管直接泵浦产生二级斯托克斯级联拉曼效应的情况。在研究的全光纤方案中，一阶斯托克斯波在950 - 954纳米处产生，该线性腔由GIF两端的两个光纤布拉格光栅（FBG）构成，由于FBG特殊的横向结构，可确保光束质量从M≈30改善至M≈2.3。二级斯托克斯波在具有通过瑞利背向散射实现随机分布反馈的线性（两个FBG）或半开放（一个FBG）腔中产生。对比表明，随机激光提供了更好的光束质量和更高的斜率效率。在最大增益（996纳米）时获得了近衍射极限光束（M≈1.6），功率高达27瓦，在978纳米的失谐波长处功率为17瓦，这表明在带有FBG的二极管泵浦GIF中进行二阶随机激光可在拉曼增益光谱范围内的宽波长范围内高效产生高质量光束。
