The average power of diode-pumped fiber lasers has been developed deeply into the kW regime in the past years.However, stimulated Raman scattering(SRS) is still a major factor limiting the further power scaling. Here,...The average power of diode-pumped fiber lasers has been developed deeply into the kW regime in the past years.However, stimulated Raman scattering(SRS) is still a major factor limiting the further power scaling. Here, we have demonstrated the mitigation of SRS in kilowatt-level diode-pumped fiber amplifiers using a chirped and tilted fiber Bragg grating(CTFBG) for the first time. The CTFBG is designed and inscribed in large-mode-area(LMA) fibers, matching with the operating wavelength of the fiber amplifier. With the CTFBG inserted between the seed laser and the amplifier stage, an SRS suppression ratio of ~10 dB is achieved in spectrum at the maximum output laser power of 2.35 kW,and there is no reduction in laser slope efficiency and degradation in beam quality. This work proves the feasibility and practicability of CTFBGs for SRS suppression in high-power fiber lasers, which is very useful for the further power scaling.展开更多
The experimental investigation of mode distortion induced by stimulated Raman scattering(SRS)in a high-power fiber amplifier,which includes the evolutions of optical spectra,spatial beam profiles,and time-frequency ch...The experimental investigation of mode distortion induced by stimulated Raman scattering(SRS)in a high-power fiber amplifier,which includes the evolutions of optical spectra,spatial beam profiles,and time-frequency characteristics,has been carried out in detail.Temporal-frequency characteristics have been studied for the first time,to the best of our knowledge,by using a low-speed camera and high-speed photodiode traces,which revealed that temporal-frequency characteristics of SRS-induced mode distortion are different from traditional dynamic mode instability(MI).The experimental results show that the output beam profile remains stable before the mode distortion occurs and fluctuates obviously after the onset of SRS-induced MI but on a time scale of seconds,which is much lower than that of Yb-gain-induced MI featuring millisecond-level beam profile fluctuation.It also shows that the mode distortion became measurable in company with the onset of inter-mode four-wave mixing(IM-FWM)when the ratio of Raman light reaches 3%;further,the beam quality factor M2degrades gradually from 1.4 to 2.1 as the ratio of Raman light increases.The mode distortion is accompanied by an obvious temperature increase of the output passive fiber,which further confirms that the mode distortion originates from SRS.The cause of the mode distortion induced by SRS has been explained in the context of core-pumped SRS effect,and the investigation on the accompanying IM-FWM effect indicates that the main content of the SRSinduced high-order mode is the LP21 mode.展开更多
We demonstrate a high-power single-frequency master oscillator power amplifier （MOPA） fiber laser.The central wavelength of the single-frequency fiber laser seed is 1 063.8 nm,with a linewidth narrower than 20 kHz a...We demonstrate a high-power single-frequency master oscillator power amplifier （MOPA） fiber laser.The central wavelength of the single-frequency fiber laser seed is 1 063.8 nm,with a linewidth narrower than 20 kHz and output power of 120 mW.By using two-stage amplification,a single-frequency fiber laser with an output power of 122 W is obtained,and the optical-optical conversion efficiency is 72%.No significant amplified spontaneous emission （ASE） or stimulated Brillouin scattering （SBS） is observed.The output power can be further increased by launching more pump power.展开更多
A modified multiple-component scattering power decomposition for analyzing polarimetric synthetic aperture radar(PolSAR)data is proposed.The modified decomposition involves two distinct steps.Firstly,ei⁃genvectors of ...A modified multiple-component scattering power decomposition for analyzing polarimetric synthetic aperture radar(PolSAR)data is proposed.The modified decomposition involves two distinct steps.Firstly,ei⁃genvectors of the coherency matrix are used to modify the scattering models.Secondly,the entropy and anisotro⁃py of targets are used to improve the volume scattering power.With the guarantee of high double-bounce scatter⁃ing power in the urban areas,the proposed algorithm effectively improves the volume scattering power of vegeta⁃tion areas.The efficacy of the modified multiple-component scattering power decomposition is validated using ac⁃tual AIRSAR PolSAR data.The scattering power obtained through decomposing the original coherency matrix and the coherency matrix after orientation angle compensation is compared with three algorithms.Results from the experiment demonstrate that the proposed decomposition yields more effective scattering power for different PolSAR data sets.展开更多
While waveguide-based light concentrators offer significant advantages,their application has not been considered an interesting option for assisting multijunction or other two-terminal tandem solar cells.In this study...While waveguide-based light concentrators offer significant advantages,their application has not been considered an interesting option for assisting multijunction or other two-terminal tandem solar cells.In this study,we present a simple yet effective approach to enhancing the output power of transfer-printed multijunction InGaP/GaAs solar cells.By utilizing a simply combinable waveguide concentrator featuring a coplanar waveguide with BaSO4 Mie scattering elements,we enable the simultaneous absorption of directly illuminated solar flux and indirectly waveguided flux.The deployment of cells is optimized for front-surface photon collection in monofacial cells.Through systematic comparisons across various waveguide parameters,supported by both experimental and theoretical quantifications,we demonstrate a remarkable improvement in the maximum output power of a 26%-efficient cell,achieving an enhancement of~93%with the integration of the optimal scattering waveguide.Additionally,a series of supplementary tests are conducted to explore the effective waveguide size,validate enhancements in arrayed cell module performance,and assess the drawbacks associated with rear illumination.These findings provide a comprehensive understanding of our proposed approach towards advancing multi-junction photovoltaics.展开更多
A Nd:YAG master oscillator power amplifier (MOPA) system, pumped by a pulse flash-lamps as the pump source of optical parametric oscillator (OPO), is employed to improve the pump beam quality of OPO pump source. A bac...A Nd:YAG master oscillator power amplifier (MOPA) system, pumped by a pulse flash-lamps as the pump source of optical parametric oscillator (OPO), is employed to improve the pump beam quality of OPO pump source. A back amplifying configuration with stimulated Brillouin scattering (SBS) phase conjugation mirror is used. OPO pump laser energy of 611 mJ/pulse with 30-ns pulse duration is obtained, and near diffraction limited beam quality is achieved. Based on the type Ⅱ degenerate non-critically phase-matched KTP crystal, the OPO is used to convert pump beam from 1.064 μm to 1.57 μm, eye-safe near infrared laser range source. 1.57-μm output energy of 209 mJ/pulse with 18-ns pulse duration is attained with a short cavity KTP OPO, when pump laser energy is approximately 611 mJ. OPO conversion efficiency is up to 38.7% when pump laser energy is approximately 200 mJ.展开更多
基金supported by the National Natural Science Foundation of China(No.11274385)
文摘The average power of diode-pumped fiber lasers has been developed deeply into the kW regime in the past years.However, stimulated Raman scattering(SRS) is still a major factor limiting the further power scaling. Here, we have demonstrated the mitigation of SRS in kilowatt-level diode-pumped fiber amplifiers using a chirped and tilted fiber Bragg grating(CTFBG) for the first time. The CTFBG is designed and inscribed in large-mode-area(LMA) fibers, matching with the operating wavelength of the fiber amplifier. With the CTFBG inserted between the seed laser and the amplifier stage, an SRS suppression ratio of ~10 dB is achieved in spectrum at the maximum output laser power of 2.35 kW,and there is no reduction in laser slope efficiency and degradation in beam quality. This work proves the feasibility and practicability of CTFBGs for SRS suppression in high-power fiber lasers, which is very useful for the further power scaling.
基金National Natural Science Foundation of China(61905226)National Key Research and Development Program of China(2017YFB1104401)。
文摘The experimental investigation of mode distortion induced by stimulated Raman scattering(SRS)in a high-power fiber amplifier,which includes the evolutions of optical spectra,spatial beam profiles,and time-frequency characteristics,has been carried out in detail.Temporal-frequency characteristics have been studied for the first time,to the best of our knowledge,by using a low-speed camera and high-speed photodiode traces,which revealed that temporal-frequency characteristics of SRS-induced mode distortion are different from traditional dynamic mode instability(MI).The experimental results show that the output beam profile remains stable before the mode distortion occurs and fluctuates obviously after the onset of SRS-induced MI but on a time scale of seconds,which is much lower than that of Yb-gain-induced MI featuring millisecond-level beam profile fluctuation.It also shows that the mode distortion became measurable in company with the onset of inter-mode four-wave mixing(IM-FWM)when the ratio of Raman light reaches 3%;further,the beam quality factor M2degrades gradually from 1.4 to 2.1 as the ratio of Raman light increases.The mode distortion is accompanied by an obvious temperature increase of the output passive fiber,which further confirms that the mode distortion originates from SRS.The cause of the mode distortion induced by SRS has been explained in the context of core-pumped SRS effect,and the investigation on the accompanying IM-FWM effect indicates that the main content of the SRSinduced high-order mode is the LP21 mode.
文摘We demonstrate a high-power single-frequency master oscillator power amplifier （MOPA） fiber laser.The central wavelength of the single-frequency fiber laser seed is 1 063.8 nm,with a linewidth narrower than 20 kHz and output power of 120 mW.By using two-stage amplification,a single-frequency fiber laser with an output power of 122 W is obtained,and the optical-optical conversion efficiency is 72%.No significant amplified spontaneous emission （ASE） or stimulated Brillouin scattering （SBS） is observed.The output power can be further increased by launching more pump power.
基金Supported by the National Natural Science Foundation of China(62376214)the Natural Science Basic Research Program of Shaanxi(2023-JC-YB-533)Foundation of Ministry of Education Key Lab.of Cognitive Radio and Information Processing(Guilin University of Electronic Technology)(CRKL200203)。
文摘A modified multiple-component scattering power decomposition for analyzing polarimetric synthetic aperture radar(PolSAR)data is proposed.The modified decomposition involves two distinct steps.Firstly,ei⁃genvectors of the coherency matrix are used to modify the scattering models.Secondly,the entropy and anisotro⁃py of targets are used to improve the volume scattering power.With the guarantee of high double-bounce scatter⁃ing power in the urban areas,the proposed algorithm effectively improves the volume scattering power of vegeta⁃tion areas.The efficacy of the modified multiple-component scattering power decomposition is validated using ac⁃tual AIRSAR PolSAR data.The scattering power obtained through decomposing the original coherency matrix and the coherency matrix after orientation angle compensation is compared with three algorithms.Results from the experiment demonstrate that the proposed decomposition yields more effective scattering power for different PolSAR data sets.
基金supported in part by the research fund of Hanyang University(HY-202300000003126)in part by the National Research Foundation of Korea(NRF)funded by the Ministry of Science,ICT under Grants RS-2023-00209380,RS-2024-00415821,NRF-2021M3H4A6A01048300,NRF-2021M3H4A1A02051253,and NRF-2022M318A2078705in part by the Technology Innovation Program(20018379,Development of high-reliability light-emitting fiber-based woven wearable displays)funded by the Ministry of Trade,Industry&Energy of the Republic of Korea.
文摘While waveguide-based light concentrators offer significant advantages,their application has not been considered an interesting option for assisting multijunction or other two-terminal tandem solar cells.In this study,we present a simple yet effective approach to enhancing the output power of transfer-printed multijunction InGaP/GaAs solar cells.By utilizing a simply combinable waveguide concentrator featuring a coplanar waveguide with BaSO4 Mie scattering elements,we enable the simultaneous absorption of directly illuminated solar flux and indirectly waveguided flux.The deployment of cells is optimized for front-surface photon collection in monofacial cells.Through systematic comparisons across various waveguide parameters,supported by both experimental and theoretical quantifications,we demonstrate a remarkable improvement in the maximum output power of a 26%-efficient cell,achieving an enhancement of~93%with the integration of the optimal scattering waveguide.Additionally,a series of supplementary tests are conducted to explore the effective waveguide size,validate enhancements in arrayed cell module performance,and assess the drawbacks associated with rear illumination.These findings provide a comprehensive understanding of our proposed approach towards advancing multi-junction photovoltaics.
基金This work was supported by the National Key Laboratory Foundation (No. 51402010301ZS62010), and Harbin Institute of Technology Science Foundation (No. HIT.2001.02).
文摘A Nd:YAG master oscillator power amplifier (MOPA) system, pumped by a pulse flash-lamps as the pump source of optical parametric oscillator (OPO), is employed to improve the pump beam quality of OPO pump source. A back amplifying configuration with stimulated Brillouin scattering (SBS) phase conjugation mirror is used. OPO pump laser energy of 611 mJ/pulse with 30-ns pulse duration is obtained, and near diffraction limited beam quality is achieved. Based on the type Ⅱ degenerate non-critically phase-matched KTP crystal, the OPO is used to convert pump beam from 1.064 μm to 1.57 μm, eye-safe near infrared laser range source. 1.57-μm output energy of 209 mJ/pulse with 18-ns pulse duration is attained with a short cavity KTP OPO, when pump laser energy is approximately 611 mJ. OPO conversion efficiency is up to 38.7% when pump laser energy is approximately 200 mJ.
