Differences in forest attributes and carbon sequestration of each organ and layer between broadleaved and conifer forests of central and outer urban areas are not well-defined,hindering the precise management of urban...Differences in forest attributes and carbon sequestration of each organ and layer between broadleaved and conifer forests of central and outer urban areas are not well-defined,hindering the precise management of urban forests and improvement of function.To clarify the effect of two forest types with different urbanization intensities,we determined differences in vegetation composition and diversity,structural traits,and carbon stocks of 152 plots(20 m×20 m)in urban park forests in Changchun,which had the largest green quantity and carbon density effectiveness.We found that 1.1-fold thicker and healthier trees,and 1.6-to 2.0-fold higher,healthier,denser,and more various shrubs but with sparser trees and herbs occurred in the central urban forests(p<0.05)than in the outer forests.The conifer forests exhibited 30–70%obviously higher tree aboveground carbon sequestration(including stem and leaf)and 20%bigger trees,especially in the outer forests(p<0.05).In contrast,1.1-to 1.5-fold higher branch stocks,healthier and more diverse trees were found in broadleaved forests of both the inner and outer forests(p<0.05).Plant size and dominant species had similarly important roles in carbon stock improvement,especially big-sized woody plants and Pinus tabuliformis.In addition,a higher number of deciduous or needle species positively affected the broadleaved forest of the central urban area and conifer forest of the outer urban area,respectively.These findings can be used to guide precise management and accelerate the improvement of urban carbon function in Northeast China in the future.展开更多
We report here the first hundred-watt continuous wave fiber gas laser in H_(2)-filled hollow-core photonic crystal fiber(PCF)by stimulated Raman scattering.The pump source is a homemade narrow-linewidth fiber oscillat...We report here the first hundred-watt continuous wave fiber gas laser in H_(2)-filled hollow-core photonic crystal fiber(PCF)by stimulated Raman scattering.The pump source is a homemade narrow-linewidth fiber oscillator with a 3 dB linewidth of 0.15 nm at the maximum output power of 380 W.To efficiently and stably couple several-hundred-watt pump power into the hollow core and seal the gas,a hollow-core fiber end-cap is fabricated and used at the input end.A maximum power of 110 W at 1153 nm is obtained in a 5 m long hollow-core PCF filled with 36 bar H2,and the conversion efficiency of the first Stokes power is around 48.9%.This work paves the way for high-power fiber gas Raman lasers.展开更多
We report here on a diode-pumped pulsed mid-infrared laser source based on gas-filled hollow-core fibers(HCFs)towards an all-fiber structure by the tapering method. The pump laser is coupled into an acetylene-filled H...We report here on a diode-pumped pulsed mid-infrared laser source based on gas-filled hollow-core fibers(HCFs)towards an all-fiber structure by the tapering method. The pump laser is coupled into an acetylene-filled HCF through a tapered single-mode fiber. By precisely tuning the wavelength of the diode to match different absorption lines of acetylene near 1.5 μm, mid-infrared emission around 3.1–3.2 μm is generated. With 2 m HCFs and3 mbar acetylene gas, a maximum average power of 130 m W is obtained with a laser slope efficiency of ~24%.This work provides a potential scheme for all-fiber mid-infrared fiber gas lasers.展开更多
Fibre lasers operating at the mid-IR have attracted enormous interest due to the plethora of applications in defence,security,medicine,and so on.However,no continuous-wave(CW)fibre lasers beyond 4μm based on rare-ear...Fibre lasers operating at the mid-IR have attracted enormous interest due to the plethora of applications in defence,security,medicine,and so on.However,no continuous-wave(CW)fibre lasers beyond 4μm based on rare-earth-doped fibres have been demonstrated thus far.Here,we report efficient mid-IR laser emission from HBr-filled silica hollow-core fibres(HCFs)for the first time.By pumping with a self-developed thulium-doped fibre amplifier seeded by several diode lasers over the range of 1940–1983 nm,narrow linewidth mid-IR emission from 3810 to 4496 nm has been achieved with a maximum laser power of about 500 mW and a slope efficiency of approximately 18%.To the best of our knowledge,the wavelength of 4496 nm with strong absorption in silica-based fibres is the longest emission wavelength from a CW fibre laser,and the span of 686 nm is also the largest tuning range achieved to date for any CW fibre laser.By further reducing the HCF transmission loss,increasing the pump power,improving the coupling efficiency,and optimizing the fibre length together with the pressure,the laser efficiency and output power are expected to increase significantly.This work opens new opportunities for broadly tunable high-power mid-IR fibre lasers,especially beyond 4μm.展开更多
Fiber gas lasers based on gas-filled hollow-core fibers(HCFs)perfectly combine the advantages of fiber lasers and gas lasers and have obtained fast development in the past years.However,stable and efficient coupling o...Fiber gas lasers based on gas-filled hollow-core fibers(HCFs)perfectly combine the advantages of fiber lasers and gas lasers and have obtained fast development in the past years.However,stable and efficient coupling of high-power pump lasers into the HCFs is one of the key problems to be solved.In this paper,we study the coupling of high-power continuous wave fiber lasers into anti-resonant HCFs through an end-cap.By optimizing the splicing parameters,a maximum laser power of 1167 W was injected into the 1-m-long HCFs,and 1021W was obtained at the output end,giving a total transmission efficiency of〜87.5%.A more than 1 h test showed the stability of such a coupling method.Meanwhile,the laser beam quality was well maintained.This work opens new opportunities for stable and highly efficient coupling of high-power lasers into HCFs,which is significant for its applications in many other fields besides high-power fiber gas lasers,such as high-power laser delivering.展开更多
We report here a single-pass 1.56 μm fiber gas Raman laser in a deuterium-filled hollow-core fiber and a 2.86 μm cascade fiber gas Raman laser with methane in the second stage.The maximum output powers at 1.56 and 2...We report here a single-pass 1.56 μm fiber gas Raman laser in a deuterium-filled hollow-core fiber and a 2.86 μm cascade fiber gas Raman laser with methane in the second stage.The maximum output powers at 1.56 and 2.86 μm are 27 and 8.5 m W with Raman conversion efficiency of 30% and 42%, respectively.The results offer a new method to produce a 1.5 μm fiber source and prove the potential of the cascade fiber gas Raman laser in extending the available wavelength.展开更多
基金the Youth Growth Technology Project,Science and Technology Department of Jilin Province(20230508130RC)Bureau of Forestry and Landscaping of Changchun.
文摘Differences in forest attributes and carbon sequestration of each organ and layer between broadleaved and conifer forests of central and outer urban areas are not well-defined,hindering the precise management of urban forests and improvement of function.To clarify the effect of two forest types with different urbanization intensities,we determined differences in vegetation composition and diversity,structural traits,and carbon stocks of 152 plots(20 m×20 m)in urban park forests in Changchun,which had the largest green quantity and carbon density effectiveness.We found that 1.1-fold thicker and healthier trees,and 1.6-to 2.0-fold higher,healthier,denser,and more various shrubs but with sparser trees and herbs occurred in the central urban forests(p<0.05)than in the outer forests.The conifer forests exhibited 30–70%obviously higher tree aboveground carbon sequestration(including stem and leaf)and 20%bigger trees,especially in the outer forests(p<0.05).In contrast,1.1-to 1.5-fold higher branch stocks,healthier and more diverse trees were found in broadleaved forests of both the inner and outer forests(p<0.05).Plant size and dominant species had similarly important roles in carbon stock improvement,especially big-sized woody plants and Pinus tabuliformis.In addition,a higher number of deciduous or needle species positively affected the broadleaved forest of the central urban area and conifer forest of the outer urban area,respectively.These findings can be used to guide precise management and accelerate the improvement of urban carbon function in Northeast China in the future.
基金supported by the National Natural Science Foundation of China(NSFC)(Nos.11974427 and 12004431)the Science and Technology Innovation Program of Hunan Province(No.2021RC4027)the Postgraduate Scientific Research Innovation Project of Hunan Province(No.CX20200017)
文摘We report here the first hundred-watt continuous wave fiber gas laser in H_(2)-filled hollow-core photonic crystal fiber(PCF)by stimulated Raman scattering.The pump source is a homemade narrow-linewidth fiber oscillator with a 3 dB linewidth of 0.15 nm at the maximum output power of 380 W.To efficiently and stably couple several-hundred-watt pump power into the hollow core and seal the gas,a hollow-core fiber end-cap is fabricated and used at the input end.A maximum power of 110 W at 1153 nm is obtained in a 5 m long hollow-core PCF filled with 36 bar H2,and the conversion efficiency of the first Stokes power is around 48.9%.This work paves the way for high-power fiber gas Raman lasers.
基金supported by the Outstanding Youth Science Fund Project of Hunan Provincial Natural Science Foundation(No.2019JJ20023)the National Natural Science Foundation of China(NSFC)(No.61705266)
文摘We report here on a diode-pumped pulsed mid-infrared laser source based on gas-filled hollow-core fibers(HCFs)towards an all-fiber structure by the tapering method. The pump laser is coupled into an acetylene-filled HCF through a tapered single-mode fiber. By precisely tuning the wavelength of the diode to match different absorption lines of acetylene near 1.5 μm, mid-infrared emission around 3.1–3.2 μm is generated. With 2 m HCFs and3 mbar acetylene gas, a maximum average power of 130 m W is obtained with a laser slope efficiency of ~24%.This work provides a potential scheme for all-fiber mid-infrared fiber gas lasers.
基金the Outstanding Youth Science Fund Project of Hunan Province Natural Science Foundation(2019JJ20023)National Natural Science Foundation of China(NSFC)(11974427,12004431)+1 种基金State Key Laboratory of Pulsed Power Laser Technology(SKL-2020-ZR05,SKL-2021-ZR01)Postgraduate Scientific Research Innovation Project of Hunan Province(CX20190026,CX20200047).
文摘Fibre lasers operating at the mid-IR have attracted enormous interest due to the plethora of applications in defence,security,medicine,and so on.However,no continuous-wave(CW)fibre lasers beyond 4μm based on rare-earth-doped fibres have been demonstrated thus far.Here,we report efficient mid-IR laser emission from HBr-filled silica hollow-core fibres(HCFs)for the first time.By pumping with a self-developed thulium-doped fibre amplifier seeded by several diode lasers over the range of 1940–1983 nm,narrow linewidth mid-IR emission from 3810 to 4496 nm has been achieved with a maximum laser power of about 500 mW and a slope efficiency of approximately 18%.To the best of our knowledge,the wavelength of 4496 nm with strong absorption in silica-based fibres is the longest emission wavelength from a CW fibre laser,and the span of 686 nm is also the largest tuning range achieved to date for any CW fibre laser.By further reducing the HCF transmission loss,increasing the pump power,improving the coupling efficiency,and optimizing the fibre length together with the pressure,the laser efficiency and output power are expected to increase significantly.This work opens new opportunities for broadly tunable high-power mid-IR fibre lasers,especially beyond 4μm.
基金This work was supported by the Outstanding Youth Science Fund of Hunan Provincial Natural Science Foundation(No.2019JJ20023)National Natural Science Foundation of China(NSFC)(Nos.11974427 and 12004431)+2 种基金State Key Laboratory of Pulsed Power Laser(Nos.SKL2020ZR05 and SKL2021ZR01)Science and Technology Innovation Program of Hunan Province(No.2021RC4027)Postgraduate Scientific Research Innovation Project of Hunan Province(No.CX20200017).
文摘Fiber gas lasers based on gas-filled hollow-core fibers(HCFs)perfectly combine the advantages of fiber lasers and gas lasers and have obtained fast development in the past years.However,stable and efficient coupling of high-power pump lasers into the HCFs is one of the key problems to be solved.In this paper,we study the coupling of high-power continuous wave fiber lasers into anti-resonant HCFs through an end-cap.By optimizing the splicing parameters,a maximum laser power of 1167 W was injected into the 1-m-long HCFs,and 1021W was obtained at the output end,giving a total transmission efficiency of〜87.5%.A more than 1 h test showed the stability of such a coupling method.Meanwhile,the laser beam quality was well maintained.This work opens new opportunities for stable and highly efficient coupling of high-power lasers into HCFs,which is significant for its applications in many other fields besides high-power fiber gas lasers,such as high-power laser delivering.
基金supported by the Outstanding Youth Science Fund Project of Natural Science Foundation of Hunan Province(No.19JJ20023)the National Natural Science Foundation of China(NSFC)(No.61705266)
文摘We report here a single-pass 1.56 μm fiber gas Raman laser in a deuterium-filled hollow-core fiber and a 2.86 μm cascade fiber gas Raman laser with methane in the second stage.The maximum output powers at 1.56 and 2.86 μm are 27 and 8.5 m W with Raman conversion efficiency of 30% and 42%, respectively.The results offer a new method to produce a 1.5 μm fiber source and prove the potential of the cascade fiber gas Raman laser in extending the available wavelength.
