Fiber optic sensing technology,with its low transmission loss,wide bandwidth,and broad dynamic range,offers significant advantages for high-sensitivity measurements.In this study,a multi-band soliton modulation system...Fiber optic sensing technology,with its low transmission loss,wide bandwidth,and broad dynamic range,offers significant advantages for high-sensitivity measurements.In this study,a multi-band soliton modulation system for stress sensing is proposed,utilizing Ti_(3)C_(2)T_(x)to generate ultrashort pulses.By applying stress to microfibers,dichromatic periodic multisoliton mode-locking at 1530 nm and 1555.2 nm is achieved.Vibrational mechanical stress further modulates cross-phase interactions between solitons,inducing higher-order bound solitons with small-amplitude oscillations.These dynamic processes reveal complex nonlinear optical behaviors and enhance sensing capabilities.Additionally,the feasibility of stable mode-locking of Ti_(3)C_(2)T_(x)in a 1µm multimode cavity is analyzed using the multimode nonlinear Schrodinger equation,and multisoliton states are experimentally demonstrated by integrating a 1µm narrow-linewidth ultrafast multimode laser with a stressed microfiber.展开更多
Inconel 738 LC samples were fabricated using laser powder bed fusion under continuous-wave and pulsed-wave modes.Microstructure,surface quality and mechanical properties were compared to evaluate the printing quality ...Inconel 738 LC samples were fabricated using laser powder bed fusion under continuous-wave and pulsed-wave modes.Microstructure,surface quality and mechanical properties were compared to evaluate the printing quality between these 2 laser beam modes.The results show that the application of pulsed wave could effectively eliminate cracking in the as-fabricated sample,despite 0.046%porosity generated.Further microstructure analysis revealed that the refinement of grains by the pulsed-wave laser beam was the main contributor in eliminating the cracks.And this refinement was ascribed to the higher cooling rate under the discontinuous radiation of laser beam proofed by the numerical simulation.And the pore formation was related to Rayleigh instability and residual bubbles in the sample under the pulsed-wave mode,while pores were less detrimental to the mechanical properties than cracks.Therefore,the part under the pulsed-wave mode exhibited superior mechanical performance compared to that under the continuous-wave mode.展开更多
Continuous-wave cavity ring-down spectroscopy(CW-CRDS)is an important technical means to monitor greenhouse gases in atmospheric environment.In this paper,a CW-CRDS system is built to meet the needs of atmospheric met...Continuous-wave cavity ring-down spectroscopy(CW-CRDS)is an important technical means to monitor greenhouse gases in atmospheric environment.In this paper,a CW-CRDS system is built to meet the needs of atmospheric methane monitoring.The problem of mode matching is explained from the perspective of transverse mode and longitudinal mode,and the influence of laser injection efficiency on measurement precision is further analyzed.The results of cavity ring-down time measurement show that the measurement precision is higher when the laser is coupled with the fundamental mode.In the experiment,DFB laser is used to calibrate the system with standard methane concentration,and the measurement residual is less than±4×10^(-4)μs^(-1).The methane concentration in the air is monitored in real time for two days.The results show the consistency of the concentration changes over the two days,which further demonstrates the reliability of the system for the measurement of trace methane.By analyzing the influence of mode matching,it not only assists the adjustment of the optical path,but also further improves the sensitivity of the system measurement.展开更多
We report on the design and fabrication of λ-7.2μm distributed feedback quantum cascade lasers lot very high temperature cw operation and low electrical power consumption. The cw operation is reported above 90℃. Fo...We report on the design and fabrication of λ-7.2μm distributed feedback quantum cascade lasers lot very high temperature cw operation and low electrical power consumption. The cw operation is reported above 90℃. For a 2-mm-long and 10-μm-wide laser coated with high-reflectivity on the rear facet, more than 170mW of output power is obtained at 20℃ with a threshold power consumption of 2.4 W, corresponding to 30mW with a threshold power consumption of 3.9 W at 90℃. Robust single-mode emission with a side-mode suppression ratio above 25 dB is continuously tunable by the heat sink temperature or injection current.展开更多
In this paper, we have demonstrated an Er-doped ultrafast laser with a single mode fiber-gradient index multimode fiber-single mode fiber(SMF-GIMF-SMF, SMS) structure as saturable absorber(SA), which can generate not ...In this paper, we have demonstrated an Er-doped ultrafast laser with a single mode fiber-gradient index multimode fiber-single mode fiber(SMF-GIMF-SMF, SMS) structure as saturable absorber(SA), which can generate not only stable single-pulse state, but also special mode-locked pulses with the characteristics of high energy and noisy behaviors at proper pump power and cavity polarization state. In addition, we have deeply investigated the real-time spectral evolutions of the mode-locked pulses through the dispersive Fourier transformation(DFT) technique. It can be found that the pulse regime can actually consist of a lot of small noise pulses with randomly varying intensities. We believe that these results will further enrich the nonlinear dynamical processes in the ultrafast lasers.展开更多
The transition state between the continuous wave region and the mode-locked region in a passively mode-locked erbium-doped fibre ring laser has been experimentally observed by utilizing the nonlinear polarization rota...The transition state between the continuous wave region and the mode-locked region in a passively mode-locked erbium-doped fibre ring laser has been experimentally observed by utilizing the nonlinear polarization rotation technique. When the pump power reaches the mode-locked threshold, the metastable pulse train with a tunable repetition rate is obtained in the transition from the continuous wave state to the passive mode-locked state via proper adjustment of the polarization controller. A simpie model has been established to explain the experimental observation.展开更多
The locking of tearing modes by the error field is studied by nonlinear numerical modeling.The threshold of mode locking for J-TEXT tokamak plasmas is found.
Synchronized dual-wavelength mode-locked laser is investigated numerically and experimentally in the normal dispersion regime.A programmable optical processor is introduced to shape the spectral profile and adjust the...Synchronized dual-wavelength mode-locked laser is investigated numerically and experimentally in the normal dispersion regime.A programmable optical processor is introduced to shape the spectral profile and adjust the net dispersion,which is demonstrated be a convenient and reliable approach to generate dual-color solitons.The time-stretch dispersive Fourier transform and frequency-resolved optical grating techniques are utilized to measure the spectral and temporal characteristics of dual-color solitons,respectively.The numerical results are consistent with experimental results.This work may facilitate the development of filter-based mode-locked laser and the understanding of multi-wavelength soliton dynamics.展开更多
CsPbBr3 nanocrystal is used as the saturable absorber(SA) for mode-locking Tm-doped fiber laser in a ring fiber cavity.The modulation depth, saturable intensity, and non-saturable loss of the fabricated SA are 14.1%, ...CsPbBr3 nanocrystal is used as the saturable absorber(SA) for mode-locking Tm-doped fiber laser in a ring fiber cavity.The modulation depth, saturable intensity, and non-saturable loss of the fabricated SA are 14.1%, 2.5 MW/cm^2,and 5.9%, respectively.In the mode-locking operation, the mode-locked pulse train has a repetition rate of 16.6 MHz with pulse width of 24.2 ps.The laser wavelength is centered at 1992.9 nm with 3-dB spectrum width of 2.5 nm.The maximum output power is 110 mW with slope efficiency of 7.1%.Our experiment shows that CsPbBr3 nanocrystal can be used as an efficient SA in the 2-μm wavelength region.展开更多
Passive harmonic mode locking of an erbium-doped fiber laser based on few-layer molybdenum disulfide(MoS2)saturable absorber(SA) is demonstrated. The few-layer MoS2 is prepared by the chemical vapor deposition(CVD) me...Passive harmonic mode locking of an erbium-doped fiber laser based on few-layer molybdenum disulfide(MoS2)saturable absorber(SA) is demonstrated. The few-layer MoS2 is prepared by the chemical vapor deposition(CVD) method and then transferred onto the end face of a fiber connector to form a fiber-compatible Mo S2SA. The 20 th harmonic modelocked pulses at 216-MHz repetition rate are stably generated with a pulse duration of 1.42 ps and side-mode suppression ratio(SMSR) of 36.1dB. The results confirm that few-layer MoS2 can serve as an effective SA for mode-locked fiber lasers.展开更多
This paper reports the periodic power variation of the pulse-train in a passively mode-locked soliton fiber ring laser. It can obtain either the uniform or nonuniform pulse-train output by simply rotating the polariza...This paper reports the periodic power variation of the pulse-train in a passively mode-locked soliton fiber ring laser. It can obtain either the uniform or nonuniform pulse-train output by simply rotating the polarization controllers. The experimental results show that the pulse-train nonuniformity is caused by the interaction between the nonuniform polarization states of the soliton pulses and the passive polarizer in the cavity.展开更多
We report on the generation of conventional and dissipative solitons in erbium-doped fiber lasers by the evanescent field interaction between the propagating light and a multilayer molybdenum disulfide（MoS_2） thin f...We report on the generation of conventional and dissipative solitons in erbium-doped fiber lasers by the evanescent field interaction between the propagating light and a multilayer molybdenum disulfide（MoS_2） thin film. The MoS_2 film is fabricated by depositing the MoS_2 water–ethanol mixture on a D-shape-fiber（DF） repetitively. The measured nonsaturable loss, saturable optical intensity, and the modulation depth of this device are 13.3%, 110 MW/cm^2, and 3.4% respectively.Owing to the very low nonsaturable loss, the laser threshold of conventional soliton is as low as 4.8 mW. The further increase of net cavity dispersion to normal regime, stable dissipation soliton pulse trains with a spectral bandwidth of 11.7 nm and pulse duration of 116 ps are successfully generated. Our experiment demonstrates that the MoS_2-DF device can indeed be used as a high performance saturable absorber for further applications in ultrafast photonics.展开更多
An all-fiber mode-locked fiber laser was achieved with a saturable absorber based on a tapered fiber deposited with layered molybdenum selenide(MoSe_2). The laser was operated at a central wavelength of 1558.35 nm wit...An all-fiber mode-locked fiber laser was achieved with a saturable absorber based on a tapered fiber deposited with layered molybdenum selenide(MoSe_2). The laser was operated at a central wavelength of 1558.35 nm with an output spectral width of 2.9 nm, and a pulse repetition rate of 16.33 MHz. To the best of our knowledge, this is the first report on mode-locked fiber lasers using MoSe_2 saturable absorbers based on tapered fibers.展开更多
A Kerr-lens mode-locked Ti：sapphire laser operating in a non-soliton regime is demonstrated. Dispersive wave generation is observed as a result of third order dispersion in the vicinity of zero dispersion. The charac...A Kerr-lens mode-locked Ti：sapphire laser operating in a non-soliton regime is demonstrated. Dispersive wave generation is observed as a result of third order dispersion in the vicinity of zero dispersion. The characteristics of the Ti：sapphire l^ser operating in a positive dispersion regime are presented, where the oscillator directly generates pulses with duration continuously tunable from 0.37 ps to 2.11 ps, and 36 fs pulses are achieved atter extracavity compression. The oscillation is numerically simulated with an extended nonlinear Schr6dinger equation, and the simulation results are in good agreement with the experimental results.展开更多
A high-gradient radiofrequency(RF)gun operated in continuous-wave(CW)mode is required in various accelerating applications.Due to the high RF power loss,a traditional normal-conducting(NC)RF electron gun has difficult...A high-gradient radiofrequency(RF)gun operated in continuous-wave(CW)mode is required in various accelerating applications.Due to the high RF power loss,a traditional normal-conducting(NC)RF electron gun has difficulty meeting the requirement of generating a high-repetition-rate electron beam.The development of a scheme for a CW NC-RF gun is urgently required.Demonstrated as a photoinjector of a high-repetition-rate free-electron laser(FEL),an electron gun operated in CW mode and the VHF band is designed.An analysis of the reentrant gun cavity is presented in this paper to increase the gradient and decrease the power density and power dissipation.Referring to the analysis results,the design of a162.5 MHz gun cavity is optimized by a multi-objective evolutionary algorithm to achieve better performance in CW mode.Multipacting and thermal analyses are also deliberated in the design to coordinate with RF and mechanical design.The optimized 162.5 MHz gun cavity can be operated in CW mode to generate a high-repetition-rate beam with voltage up to 1 MV and gradient up to 32.75 MV/m at the cathode.展开更多
An environmentally stable, repetition rate tunable, all-polarization-maintaining, Er-doped pulse fiber laser with a single-wall carbon nanotubes saturated absorber is demonstrated. The ring laser cavity includes a del...An environmentally stable, repetition rate tunable, all-polarization-maintaining, Er-doped pulse fiber laser with a single-wall carbon nanotubes saturated absorber is demonstrated. The ring laser cavity includes a delay line enabling a tunable repetition rate to vary from 35.52 MHz to 35.64 MHz with continuous mode-locked operation. The laser output parameters confirm that the tunable mode-locked operations are stable. High environmental stability is also confirmed by the -130 dBc/Hz low phase noise, a 70-dB signal-to-noise ratio of radio frequency signals, a low amplitude fluctuation of 5.76 × 10-4, and a low fluctuation of reoetition rate of 12 Hz. The laser shows a high de^ree of oolarization of 93%.展开更多
This paper demonstrates the passively mode-locked Nd：GdVO4 laser operating on the ^4F3/2-^4I9/2 transition at 912 nm by using a semiconductor saturable-absorber mirror for passive mode locking, stable continuous wave...This paper demonstrates the passively mode-locked Nd：GdVO4 laser operating on the ^4F3/2-^4I9/2 transition at 912 nm by using a semiconductor saturable-absorber mirror for passive mode locking, stable continuous wave modelocked 912nm laser was achieved with a repetition rate of 176 MHz. At the incident pump power of 17.7W, 22.6mW average output power of stable mode-locked laser was obtained with a slope efficiency of 0.3%.展开更多
The effects of externally applied resonant magnetic perturbation (RMP) on the locked mode of the neoclassical tearing mode (NTM) are numerically investigated by means of a set of reduced magnetohydrodynamic equations....The effects of externally applied resonant magnetic perturbation (RMP) on the locked mode of the neoclassical tearing mode (NTM) are numerically investigated by means of a set of reduced magnetohydrodynamic equations.It is found that,for a small bootstrap current fraction,three regimes,namely the slight suppression regime,the small locked island (SLI) regime and the big locked island (BLI) regime,are discovered with the increase of RMP strength.For a much higher bootstrap current fraction,however,a new oscillation regime appears instead of the SLI regime,although the other regimes still remain.The physical process in each regime is analyzed in detail based on the phase difference between the NTM and the RMP.Moreover,the critical values of the RMP in both SLI and BLI regimes are obtained,and their dependence on key plasma parameters is discussed as well.展开更多
Magnetohydrodynamic(MHD)instabilities are widely observed during tokamak plasma operation.Magnetic diagnostics provide important information which supports the understanding and control of MHD instabilities.This paper...Magnetohydrodynamic(MHD)instabilities are widely observed during tokamak plasma operation.Magnetic diagnostics provide important information which supports the understanding and control of MHD instabilities.This paper presents the current status of the magnetic diagnostics dedicated to measuring MHD instabilities at the J-TEXT tokamak;the diagnostics consist of five Mirnov probe arrays for measuring high-frequency magnetic perturbations and two saddle-loop arrays for low-frequency magnetic perturbations,such as the locked mode.In recent years,several changes have been made to these arrays.The structure of the probes in the poloidal Mirnov arrays has been optimized to improve their mechanical strength,and the number of in-vessel saddle loops has also been improved to support better spatial resolution.Due to the installation of high-field-side(HFS)divertor targets in early 2019,some of the probes were removed,but an HFS Mirnov array was designed and installed behind the targets.Owing to its excellent toroidal symmetry,the HFS Mirnov array has,for the first time at J-TEXT,provided valuable new information about the locked mode and the quasi-static mode(QSM)in the HFS.Besides,various groups of magnetic diagnostics at different poloidal locations have been systematically used to measure the QSM,which confirmed the poloidal mode number m and the helical structure of the QSM.By including the HFS information,the 2/1 resonant magnetic perturbation(RMP)-induced locked mode was measured to have a poloidal mode number m of~2.展开更多
We demonstrated a scheme of phase-locked terahertz quantum cascade lasers(THz QCLs)array,with a single-mode pulse power of 108 mW at 13 K.The device utilizes a Talbot cavity to achieve phase locking among five ridge l...We demonstrated a scheme of phase-locked terahertz quantum cascade lasers(THz QCLs)array,with a single-mode pulse power of 108 mW at 13 K.The device utilizes a Talbot cavity to achieve phase locking among five ridge lasers with first-order buried distributed feedback(DFB)grating,resulting in nearly five times amplification of the single-mode power.Due to the optimum length of Talbot cavity depends on wavelength,the combination of Talbot cavity with the DFB grating leads to better power amplification than the combination with multimode Fabry-Perot(F-P)cavities.The Talbot cavity facet reflects light back to the ridge array direction and achieves self-imaging in the array,enabling phase-locked operation of ridges.We set the spacing between adjacent elements to be 220μm,much larger than the free-space wavelength,ensuring the operation of the fundamental supermode throughout the laser's dynamic range and obtaining a high-brightness far-field distribution.This scheme provides a new approach for enhancing the single-mode power of THz QCLs.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12275240,12261131495,and 12475008)the Natural Science Foundation of Zhejiang Province(Grant No.LY24A050002).
文摘Fiber optic sensing technology,with its low transmission loss,wide bandwidth,and broad dynamic range,offers significant advantages for high-sensitivity measurements.In this study,a multi-band soliton modulation system for stress sensing is proposed,utilizing Ti_(3)C_(2)T_(x)to generate ultrashort pulses.By applying stress to microfibers,dichromatic periodic multisoliton mode-locking at 1530 nm and 1555.2 nm is achieved.Vibrational mechanical stress further modulates cross-phase interactions between solitons,inducing higher-order bound solitons with small-amplitude oscillations.These dynamic processes reveal complex nonlinear optical behaviors and enhance sensing capabilities.Additionally,the feasibility of stable mode-locking of Ti_(3)C_(2)T_(x)in a 1µm multimode cavity is analyzed using the multimode nonlinear Schrodinger equation,and multisoliton states are experimentally demonstrated by integrating a 1µm narrow-linewidth ultrafast multimode laser with a stressed microfiber.
基金financially supported by National Natural Science Foundation of China(No.91860131 and No.52074157)National Key Research and Development Program of China(No.2017YFB0702901)+1 种基金Shenzhen Science and Technology Innovation Commission under the Projects(No.JCYJ20170817111811303,No.KQTD20170328154443162 and ZDSYS201703031748354)joint Ph.D.program between SUSTech and UoB(No.FEFE/GAS1792)。
文摘Inconel 738 LC samples were fabricated using laser powder bed fusion under continuous-wave and pulsed-wave modes.Microstructure,surface quality and mechanical properties were compared to evaluate the printing quality between these 2 laser beam modes.The results show that the application of pulsed wave could effectively eliminate cracking in the as-fabricated sample,despite 0.046%porosity generated.Further microstructure analysis revealed that the refinement of grains by the pulsed-wave laser beam was the main contributor in eliminating the cracks.And this refinement was ascribed to the higher cooling rate under the discontinuous radiation of laser beam proofed by the numerical simulation.And the pore formation was related to Rayleigh instability and residual bubbles in the sample under the pulsed-wave mode,while pores were less detrimental to the mechanical properties than cracks.Therefore,the part under the pulsed-wave mode exhibited superior mechanical performance compared to that under the continuous-wave mode.
基金This research is financial supported by the Natural National Science Foundation of China(Grant Nos.11874364,41877311,and 42005107)the National Key Research and Development Program of China(Grant No.2017YFC0805004)the CAS&Bengbu Technology Transfer Project(Grant No.ZKBB202102).
文摘Continuous-wave cavity ring-down spectroscopy(CW-CRDS)is an important technical means to monitor greenhouse gases in atmospheric environment.In this paper,a CW-CRDS system is built to meet the needs of atmospheric methane monitoring.The problem of mode matching is explained from the perspective of transverse mode and longitudinal mode,and the influence of laser injection efficiency on measurement precision is further analyzed.The results of cavity ring-down time measurement show that the measurement precision is higher when the laser is coupled with the fundamental mode.In the experiment,DFB laser is used to calibrate the system with standard methane concentration,and the measurement residual is less than±4×10^(-4)μs^(-1).The methane concentration in the air is monitored in real time for two days.The results show the consistency of the concentration changes over the two days,which further demonstrates the reliability of the system for the measurement of trace methane.By analyzing the influence of mode matching,it not only assists the adjustment of the optical path,but also further improves the sensitivity of the system measurement.
基金Supported by the National Basic Research Program of China under Grant No 2013CB632801the National Key Research and Development Program under Grant No 2016YFB0402303+2 种基金the National Natural Science Foundation of China under Grant Nos61435014,61627822,61574136 and 61306058the Key Projects of Chinese Academy of Sciences under Grant No ZDRW-XH-2016-4the Beijing Natural Science Foundation under Grant No 4162060
文摘We report on the design and fabrication of λ-7.2μm distributed feedback quantum cascade lasers lot very high temperature cw operation and low electrical power consumption. The cw operation is reported above 90℃. For a 2-mm-long and 10-μm-wide laser coated with high-reflectivity on the rear facet, more than 170mW of output power is obtained at 20℃ with a threshold power consumption of 2.4 W, corresponding to 30mW with a threshold power consumption of 3.9 W at 90℃. Robust single-mode emission with a side-mode suppression ratio above 25 dB is continuously tunable by the heat sink temperature or injection current.
基金supported by the Guangdong Basic and Applied Basic Research Foundation (No.2023A1515010093)the Shenzhen Fundamental Research Program (Stable Support Plan Program)(Nos.JCYJ20220809170611004, 20231121110828001 and 20231121113641002)the National Taipei University of Technology-Shenzhen University Joint Research Program (No.2024001)。
文摘In this paper, we have demonstrated an Er-doped ultrafast laser with a single mode fiber-gradient index multimode fiber-single mode fiber(SMF-GIMF-SMF, SMS) structure as saturable absorber(SA), which can generate not only stable single-pulse state, but also special mode-locked pulses with the characteristics of high energy and noisy behaviors at proper pump power and cavity polarization state. In addition, we have deeply investigated the real-time spectral evolutions of the mode-locked pulses through the dispersive Fourier transformation(DFT) technique. It can be found that the pulse regime can actually consist of a lot of small noise pulses with randomly varying intensities. We believe that these results will further enrich the nonlinear dynamical processes in the ultrafast lasers.
基金Project supported by the National Natural Science Foundation of China(Grant No.11074078)the Specialized Research Fund for the Doctoral Program of Higher Education,China(Grant No.20094407110002)+1 种基金the Key Program for Scientific and Technological Innovations of Higher Education Institutes in Guangdong Province,China(Grant No.cxzd1011)the Foundation for Distinguished Young Talents in Higher Education of Guangdong,China(Grant No.C10183)
文摘The transition state between the continuous wave region and the mode-locked region in a passively mode-locked erbium-doped fibre ring laser has been experimentally observed by utilizing the nonlinear polarization rotation technique. When the pump power reaches the mode-locked threshold, the metastable pulse train with a tunable repetition rate is obtained in the transition from the continuous wave state to the passive mode-locked state via proper adjustment of the polarization controller. A simpie model has been established to explain the experimental observation.
基金by the National Natural Science Foundation of China under Grant No 10805022the ITER Special Foundation(2009GB105003,2010GB108004)the National Basic Research Program of China under Grant No 2008CB717805.
文摘The locking of tearing modes by the error field is studied by nonlinear numerical modeling.The threshold of mode locking for J-TEXT tokamak plasmas is found.
基金Project supported by the Innovation Program for Quantum Science and Technology(Grant No.2023ZD0301000)the National Natural Science Foundation of China(Grant Nos.12434018,62475073,1243000542,11621404,11561121003,11727812,61775059,12074122,62405090,62035005,and 11704123)+1 种基金the Natural Science Foundation of Shanghai(Grant No.23ZR1419000)China Postdoctoral Science Foundation(Grant Nos.2023M741188 and 2024T170275)。
文摘Synchronized dual-wavelength mode-locked laser is investigated numerically and experimentally in the normal dispersion regime.A programmable optical processor is introduced to shape the spectral profile and adjust the net dispersion,which is demonstrated be a convenient and reliable approach to generate dual-color solitons.The time-stretch dispersive Fourier transform and frequency-resolved optical grating techniques are utilized to measure the spectral and temporal characteristics of dual-color solitons,respectively.The numerical results are consistent with experimental results.This work may facilitate the development of filter-based mode-locked laser and the understanding of multi-wavelength soliton dynamics.
基金Project supported by the National Key R&D Program of China(Grant No.2018YFB0504500)the National Natural Science Foundation of China(Grant Nos.51472162,51672177,and 61475171)the Talent Introduction Research Project of Shanghai Institute of Technology,China(Grant No.YJ 2018-8)
文摘CsPbBr3 nanocrystal is used as the saturable absorber(SA) for mode-locking Tm-doped fiber laser in a ring fiber cavity.The modulation depth, saturable intensity, and non-saturable loss of the fabricated SA are 14.1%, 2.5 MW/cm^2,and 5.9%, respectively.In the mode-locking operation, the mode-locked pulse train has a repetition rate of 16.6 MHz with pulse width of 24.2 ps.The laser wavelength is centered at 1992.9 nm with 3-dB spectrum width of 2.5 nm.The maximum output power is 110 mW with slope efficiency of 7.1%.Our experiment shows that CsPbBr3 nanocrystal can be used as an efficient SA in the 2-μm wavelength region.
基金supported by the National Natural Science Foundation of China(Grant Nos.61378028,61421002,61475030,and 61377042)the National Basic Research Program of China(Grant No.2012CB315701)the New Century Excellent Talents Program in University,China(Grant No.NCET-13-0092)
文摘Passive harmonic mode locking of an erbium-doped fiber laser based on few-layer molybdenum disulfide(MoS2)saturable absorber(SA) is demonstrated. The few-layer MoS2 is prepared by the chemical vapor deposition(CVD) method and then transferred onto the end face of a fiber connector to form a fiber-compatible Mo S2SA. The 20 th harmonic modelocked pulses at 216-MHz repetition rate are stably generated with a pulse duration of 1.42 ps and side-mode suppression ratio(SMSR) of 36.1dB. The results confirm that few-layer MoS2 can serve as an effective SA for mode-locked fiber lasers.
基金Project supported by the Natural Science Foundation of Guangdong Province,China (Grant No 04010397)
文摘This paper reports the periodic power variation of the pulse-train in a passively mode-locked soliton fiber ring laser. It can obtain either the uniform or nonuniform pulse-train output by simply rotating the polarization controllers. The experimental results show that the pulse-train nonuniformity is caused by the interaction between the nonuniform polarization states of the soliton pulses and the passive polarizer in the cavity.
基金Project supported by the National Natural Science Foundation of China(Grant No.61378024)
文摘We report on the generation of conventional and dissipative solitons in erbium-doped fiber lasers by the evanescent field interaction between the propagating light and a multilayer molybdenum disulfide（MoS_2） thin film. The MoS_2 film is fabricated by depositing the MoS_2 water–ethanol mixture on a D-shape-fiber（DF） repetitively. The measured nonsaturable loss, saturable optical intensity, and the modulation depth of this device are 13.3%, 110 MW/cm^2, and 3.4% respectively.Owing to the very low nonsaturable loss, the laser threshold of conventional soliton is as low as 4.8 mW. The further increase of net cavity dispersion to normal regime, stable dissipation soliton pulse trains with a spectral bandwidth of 11.7 nm and pulse duration of 116 ps are successfully generated. Our experiment demonstrates that the MoS_2-DF device can indeed be used as a high performance saturable absorber for further applications in ultrafast photonics.
基金Project supported by the National Key Research and Development Program of China(Grant No.2018YFB0504500)the National Natural Science Foundation of China(Grant Nos.61475171,61705244,61307056,and 61875052)the Natural Science Foundation of Shanghai,China(Grant Nos.17ZR1433900 and17ZR1434200)
文摘An all-fiber mode-locked fiber laser was achieved with a saturable absorber based on a tapered fiber deposited with layered molybdenum selenide(MoSe_2). The laser was operated at a central wavelength of 1558.35 nm with an output spectral width of 2.9 nm, and a pulse repetition rate of 16.33 MHz. To the best of our knowledge, this is the first report on mode-locked fiber lasers using MoSe_2 saturable absorbers based on tapered fibers.
基金Project supported by the National Basic Research Program of China (Grant No. 2006CB806002)the National High Technology Research and Development Program of China (Grant No. 2007AA03Z447)+3 种基金National Natural Science Foundation of China (Grant Nos. 60678012 and 60838004)the Foundation for Key Program of Ministry of Education, China (Grant No. 108032)FANEDD(Grant No. 2007B34)NCET (Grant No. NCET-07-0597)
文摘A Kerr-lens mode-locked Ti：sapphire laser operating in a non-soliton regime is demonstrated. Dispersive wave generation is observed as a result of third order dispersion in the vicinity of zero dispersion. The characteristics of the Ti：sapphire l^ser operating in a positive dispersion regime are presented, where the oscillator directly generates pulses with duration continuously tunable from 0.37 ps to 2.11 ps, and 36 fs pulses are achieved atter extracavity compression. The oscillation is numerically simulated with an extended nonlinear Schr6dinger equation, and the simulation results are in good agreement with the experimental results.
文摘A high-gradient radiofrequency(RF)gun operated in continuous-wave(CW)mode is required in various accelerating applications.Due to the high RF power loss,a traditional normal-conducting(NC)RF electron gun has difficulty meeting the requirement of generating a high-repetition-rate electron beam.The development of a scheme for a CW NC-RF gun is urgently required.Demonstrated as a photoinjector of a high-repetition-rate free-electron laser(FEL),an electron gun operated in CW mode and the VHF band is designed.An analysis of the reentrant gun cavity is presented in this paper to increase the gradient and decrease the power density and power dissipation.Referring to the analysis results,the design of a162.5 MHz gun cavity is optimized by a multi-objective evolutionary algorithm to achieve better performance in CW mode.Multipacting and thermal analyses are also deliberated in the design to coordinate with RF and mechanical design.The optimized 162.5 MHz gun cavity can be operated in CW mode to generate a high-repetition-rate beam with voltage up to 1 MV and gradient up to 32.75 MV/m at the cathode.
文摘An environmentally stable, repetition rate tunable, all-polarization-maintaining, Er-doped pulse fiber laser with a single-wall carbon nanotubes saturated absorber is demonstrated. The ring laser cavity includes a delay line enabling a tunable repetition rate to vary from 35.52 MHz to 35.64 MHz with continuous mode-locked operation. The laser output parameters confirm that the tunable mode-locked operations are stable. High environmental stability is also confirmed by the -130 dBc/Hz low phase noise, a 70-dB signal-to-noise ratio of radio frequency signals, a low amplitude fluctuation of 5.76 × 10-4, and a low fluctuation of reoetition rate of 12 Hz. The laser shows a high de^ree of oolarization of 93%.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 60225005, 60308001, 60321003 and 60490280）.
文摘This paper demonstrates the passively mode-locked Nd：GdVO4 laser operating on the ^4F3/2-^4I9/2 transition at 912 nm by using a semiconductor saturable-absorber mirror for passive mode locking, stable continuous wave modelocked 912nm laser was achieved with a repetition rate of 176 MHz. At the incident pump power of 17.7W, 22.6mW average output power of stable mode-locked laser was obtained with a slope efficiency of 0.3%.
基金National Key R&D Program of China (Nos. 2017YFE0301900 and 2017YFE0301100)National Natural Science Foundation of China (No. 11675083)+1 种基金the Fundamental Research Funds for the Central Universities (Nos. DUT18ZD101 and DUT17LK38)the Dalian Youth Science and Technology Project Support Program (No. 2015R01).
文摘The effects of externally applied resonant magnetic perturbation (RMP) on the locked mode of the neoclassical tearing mode (NTM) are numerically investigated by means of a set of reduced magnetohydrodynamic equations.It is found that,for a small bootstrap current fraction,three regimes,namely the slight suppression regime,the small locked island (SLI) regime and the big locked island (BLI) regime,are discovered with the increase of RMP strength.For a much higher bootstrap current fraction,however,a new oscillation regime appears instead of the SLI regime,although the other regimes still remain.The physical process in each regime is analyzed in detail based on the phase difference between the NTM and the RMP.Moreover,the critical values of the RMP in both SLI and BLI regimes are obtained,and their dependence on key plasma parameters is discussed as well.
基金supported by the National MCF Energy R&D Program of China(No.2018YFE0309100)National Natural Science Foundation of China(NSFC)(No.11905078)‘the Fundamental Research Funds for the Central Universities’(No.2020kfy XJJS003)。
文摘Magnetohydrodynamic(MHD)instabilities are widely observed during tokamak plasma operation.Magnetic diagnostics provide important information which supports the understanding and control of MHD instabilities.This paper presents the current status of the magnetic diagnostics dedicated to measuring MHD instabilities at the J-TEXT tokamak;the diagnostics consist of five Mirnov probe arrays for measuring high-frequency magnetic perturbations and two saddle-loop arrays for low-frequency magnetic perturbations,such as the locked mode.In recent years,several changes have been made to these arrays.The structure of the probes in the poloidal Mirnov arrays has been optimized to improve their mechanical strength,and the number of in-vessel saddle loops has also been improved to support better spatial resolution.Due to the installation of high-field-side(HFS)divertor targets in early 2019,some of the probes were removed,but an HFS Mirnov array was designed and installed behind the targets.Owing to its excellent toroidal symmetry,the HFS Mirnov array has,for the first time at J-TEXT,provided valuable new information about the locked mode and the quasi-static mode(QSM)in the HFS.Besides,various groups of magnetic diagnostics at different poloidal locations have been systematically used to measure the QSM,which confirmed the poloidal mode number m and the helical structure of the QSM.By including the HFS information,the 2/1 resonant magnetic perturbation(RMP)-induced locked mode was measured to have a poloidal mode number m of~2.
基金funded by National Natural Science Foundation of China, grant numbers 62335006, 62274014, 62235016, 61734006, 61835011, 61991430funded by Key Program of the Chinese Academy of Sciences, grant numbers XDB43000000, QYZDJSSW-JSC027Beijing Municipal Science & Technology Commission, grant number Z221100002722018
文摘We demonstrated a scheme of phase-locked terahertz quantum cascade lasers(THz QCLs)array,with a single-mode pulse power of 108 mW at 13 K.The device utilizes a Talbot cavity to achieve phase locking among five ridge lasers with first-order buried distributed feedback(DFB)grating,resulting in nearly five times amplification of the single-mode power.Due to the optimum length of Talbot cavity depends on wavelength,the combination of Talbot cavity with the DFB grating leads to better power amplification than the combination with multimode Fabry-Perot(F-P)cavities.The Talbot cavity facet reflects light back to the ridge array direction and achieves self-imaging in the array,enabling phase-locked operation of ridges.We set the spacing between adjacent elements to be 220μm,much larger than the free-space wavelength,ensuring the operation of the fundamental supermode throughout the laser's dynamic range and obtaining a high-brightness far-field distribution.This scheme provides a new approach for enhancing the single-mode power of THz QCLs.
