Power scaling based on traditional ytterbium-doped fibers(YDFs)is limited by optical nonlinear effects and transverse mode instability(TMI)in high-power fiber lasers.Here,we propose a novel long tapered fiber with a c...Power scaling based on traditional ytterbium-doped fibers(YDFs)is limited by optical nonlinear effects and transverse mode instability(TMI)in high-power fiber lasers.Here,we propose a novel long tapered fiber with a constant cladding and tapered core(CCTC)along its axis direction.The tapered-core region of the fiber is designed to enhance the stimulated Raman scattering(SRS)threshold and suppress higher-order mode resonance in the laser cavity.The CCTC YDF was fabricated successfully with a modified chemical vapor deposition(MCVD)method combined with solution doping technology,which has a cladding diameter of 400µm and a varying core with a diameter of~24μm at both ends and~31μm in the middle.To test the performance of the CCTC fiber during high-power operation,an all-fiber laser oscillator based on a CCTC YDF was investigated experimentally.As a result,a maximum output power of 3.42 kW was achieved with an optical-to-optical efficiency of 55.2%,although the TMI effect was observed at an output power of~3.12 kW.The measured beam quality(M^(2)factor)was~1.7,and no sign of the Raman component was observed in the spectrum.We believe that CCTC YDF has great potential to simultaneously mitigate the SRS and TMI effects,and further power scaling is promising by optimizing the structure of the YDF.展开更多
A visible-light-induced metal-free desulfurization method for thiols and disulfides has been explored.This radical desulfurization features mild conditions,robustness,and excellent functionality compatibility.It was s...A visible-light-induced metal-free desulfurization method for thiols and disulfides has been explored.This radical desulfurization features mild conditions,robustness,and excellent functionality compatibility.It was successfully applied not only to the desulfurization of small molecules,but also to peptides.展开更多
The radical suppression of the photodarkening effect and laser performance deterioration via H2 loading were demonstrated in high-power Yb-doped fiber(YDF)amplifiers.The photodarkening loss at equilibrium was114.4 d B...The radical suppression of the photodarkening effect and laser performance deterioration via H2 loading were demonstrated in high-power Yb-doped fiber(YDF)amplifiers.The photodarkening loss at equilibrium was114.4 d B/m at 702 nm in the pristine fiber,while it vanished in the H2-loaded fiber.To obtain a deeper understanding of the impact of photodarkening on laser properties,the evolution of the mode instability threshold and output power in fiber amplifiers was investigated.After pumping for 300 min,the mode instability threshold of the pristine fiber dropped from 770 to 612 W,and the periodic fluctuation of the output power became intense,finally reaching 100 W.To address the detrimental effects originating from photodarkening,H2 loading was applied in contrast experiments.The output power remained stable,and no sign of mode instability was observed in the H2-loaded fiber.Moreover,the transmittance at 638 nm confirmed the absence of the photodarkening effect.The results pave the way for the further development of high-power fiber lasers.展开更多
基金the National Natural Science Foundation of China(Nos.61735007 and 61705266).
文摘Power scaling based on traditional ytterbium-doped fibers(YDFs)is limited by optical nonlinear effects and transverse mode instability(TMI)in high-power fiber lasers.Here,we propose a novel long tapered fiber with a constant cladding and tapered core(CCTC)along its axis direction.The tapered-core region of the fiber is designed to enhance the stimulated Raman scattering(SRS)threshold and suppress higher-order mode resonance in the laser cavity.The CCTC YDF was fabricated successfully with a modified chemical vapor deposition(MCVD)method combined with solution doping technology,which has a cladding diameter of 400µm and a varying core with a diameter of~24μm at both ends and~31μm in the middle.To test the performance of the CCTC fiber during high-power operation,an all-fiber laser oscillator based on a CCTC YDF was investigated experimentally.As a result,a maximum output power of 3.42 kW was achieved with an optical-to-optical efficiency of 55.2%,although the TMI effect was observed at an output power of~3.12 kW.The measured beam quality(M^(2)factor)was~1.7,and no sign of the Raman component was observed in the spectrum.We believe that CCTC YDF has great potential to simultaneously mitigate the SRS and TMI effects,and further power scaling is promising by optimizing the structure of the YDF.
基金We thank Shanghai Jiao Tong University and the National"1000-Youth Talents Plan"for financial support.
文摘A visible-light-induced metal-free desulfurization method for thiols and disulfides has been explored.This radical desulfurization features mild conditions,robustness,and excellent functionality compatibility.It was successfully applied not only to the desulfurization of small molecules,but also to peptides.
基金National Natural Science Foundation of China(61735007)National Key Research and Development Program of China(2017YFB1104400)。
文摘The radical suppression of the photodarkening effect and laser performance deterioration via H2 loading were demonstrated in high-power Yb-doped fiber(YDF)amplifiers.The photodarkening loss at equilibrium was114.4 d B/m at 702 nm in the pristine fiber,while it vanished in the H2-loaded fiber.To obtain a deeper understanding of the impact of photodarkening on laser properties,the evolution of the mode instability threshold and output power in fiber amplifiers was investigated.After pumping for 300 min,the mode instability threshold of the pristine fiber dropped from 770 to 612 W,and the periodic fluctuation of the output power became intense,finally reaching 100 W.To address the detrimental effects originating from photodarkening,H2 loading was applied in contrast experiments.The output power remained stable,and no sign of mode instability was observed in the H2-loaded fiber.Moreover,the transmittance at 638 nm confirmed the absence of the photodarkening effect.The results pave the way for the further development of high-power fiber lasers.
