In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four me...In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four metals with distinctly different thermal conductivities, i.e., titanium, nickel, molybdenum, and copper, are selected as light absorbers. The lap welding is conducted with an 808 nm diode laser and simulation experiments are also conducted. Nickel electroplating test is carried out to minimize the side-effects from different light absorptivities of different metals. The results show that the welding with an absorber of higher thermal conductivity can accommodate higher laser input power before smoking, which produces a wider and stronger welding seam.The positive role of the higher thermal conductivity can be attributed to the fact that a desirable thermal field distribution for the molecular diffusion and entanglement is produced from the case with a high thermal conductivity.展开更多
We numerically investigate the seven-core photonic crystal fiber (PCF) with the zero dispersion wavelength designed in the range of 1000 - 1080 nm, particularly suitable for the ytterbium-doped fiber laser pumping. Al...We numerically investigate the seven-core photonic crystal fiber (PCF) with the zero dispersion wavelength designed in the range of 1000 - 1080 nm, particularly suitable for the ytterbium-doped fiber laser pumping. Also, the PCFs are well designed for obtaining a flat in-phase mode by carefully adjusting the diameter of inner layer six holes, and the corresponding empirical values of fiber structure are summarized and listed. The variations of inner six holes to the amplitude of in-phase mode are further investigated, and our results show that a better tolerance can be achieved in the fiber structures with lower filling ratio configuration.展开更多
An integrated system has been provided with a-Si/H solar cells as energy conversion device,NiCo2O4 battery-supercapacitor hybrid(BSH)as energy storage device,and light emitting diodes(LEDs)as energy utilization device...An integrated system has been provided with a-Si/H solar cells as energy conversion device,NiCo2O4 battery-supercapacitor hybrid(BSH)as energy storage device,and light emitting diodes(LEDs)as energy utilization device.By designing three-dimensional hierarchical NiCo2O4 arrays as faradic electrode,with capacitive electrode of active carbon(AC),BSHs were assembled with energy density of 16.6 Wh kg-1,power density of 7285 W kg-1,long-term stability with 100% retention after 15,000 cycles,and rather low self-discharge.The NiCo2O4//AC BSH was charged to 1.6 V in 1 s by solar cells and acted as reliable sources for powering LEDs.The integrated system is rational for operation,having an overall efficiency of 8.1% with storage efficiency of 74.24%.The integrated system demonstrates a stable solar power conversion,outstanding energy storage behavior,and reliable light emitting.Our study offers a precious strategy to design a self-driven integrated system for highly efficient energy utilization.展开更多
The design, fabrication and performance of narrow-band rugate minus filters are investigated in this paper. A method of fabricating graded-index coatings by rapidly alternating deposition of low(Si O2) and high(Al2 O3...The design, fabrication and performance of narrow-band rugate minus filters are investigated in this paper. A method of fabricating graded-index coatings by rapidly alternating deposition of low(Si O2) and high(Al2 O3) refractive index materials is presented to fabricate a rugate structure. The narrow-band rugate minus filter design and fabrication approaches are discussed in detail. The experimental results, including transmittance spectrum, surface damage test and damage morphology investigated with a scanning electron microscope, demonstrate the high performance of the as-fabricated spatial filter and confirm the feasibility of the fabrication method for narrow-band rugate minus filters.展开更多
We present a high power diode-pumped continuous-wave Tm:YLF(Tm^(3+)-doped lithium yttrium fluoride) laser with a piece of silicon wafer as the output coupler(Si-OC laser) directly.Under the pump power of 40 W at 793 n...We present a high power diode-pumped continuous-wave Tm:YLF(Tm^(3+)-doped lithium yttrium fluoride) laser with a piece of silicon wafer as the output coupler(Si-OC laser) directly.Under the pump power of 40 W at 793 nm,a maximum output power of 12.1 W is obtained with a beam quality of M^2 ≤ 1.55 at 1887 nm,corresponding to an optical-to-optical efficiency of 30.25%and a slope efficiency of 33.21%.To the best of our knowledge,this is the first report on directly utilizing silicon as an output coupler(Si-OC) in the solid Tm:YLF laser system.Due to the intriguing characteristics of silicon,such as negligible absorption in the wavelength region around 2 μm,high damage threshold,low cost and long-pass filter properties,double-side polished monocrystalline silicon wafer is considered as an outstanding candidate output coupler in the high-power laser system 2 μm spectral region,which may dramatically reduce the total manufacturing costs of the 2 μm laser system.展开更多
Ultrafast pulse generation was demonstrated in thulium doped fiber laser mode locked by magnetron sputtering deposited Sb_2Te_3with the modulation depth,non-saturable loss,and saturable intensity of 38%,31.2%,and 3.3 ...Ultrafast pulse generation was demonstrated in thulium doped fiber laser mode locked by magnetron sputtering deposited Sb_2Te_3with the modulation depth,non-saturable loss,and saturable intensity of 38%,31.2%,and 3.3 MW/cm^2,respectively.Stable soliton pulses emitting at 1930.07 nm were obtained with pulse duration of 1.24 ps,a 3-dB spectral bandwidth of 3.87 nm,an average output power of 130 m W,and signal-to-noise ratio(SNR)of 84 dB.To our knowledge,this is the first demonstration of Sb_2Te_3-based SA in fiber lasers at 2-μm regime.展开更多
A switchable multi-wavelength erbium-doped photonic crystal fiber laser with a linear cavity configuration based on a Sagnac loop mirror is proposed and demonstrated experimentally.The laser is based on saturated spec...A switchable multi-wavelength erbium-doped photonic crystal fiber laser with a linear cavity configuration based on a Sagnac loop mirror is proposed and demonstrated experimentally.The laser is based on saturated spectral hole burning and the polarization hole burning effects can be switched among single-wavelength,dual-wavelength,triple-wavelength and quadruple-wavelength outputs at room temperature.The wavelength period of the output spectrum is easily varied by using polarization maintaining fibers of different lengths.The proposed fiber laser has a signal-to-noise ratio of higher than 30 dB and achieves a low threshold power of 37 mW.The power fluctuations of the lasing lines are less than 0.54 dB,1.7 dB and 2.9 dB when the laser operates at single-wavelength,dual-wavelength and triple-wavelength for one hour.展开更多
We report a cladding-pumped Tm^(3+)-doped domestic silica fiber laser operated at 2pm and actively Q-switched with an acousto-optic modulator.Pulse trains are obtained as pumped by a 785nm laser diode.The maximum aver...We report a cladding-pumped Tm^(3+)-doped domestic silica fiber laser operated at 2pm and actively Q-switched with an acousto-optic modulator.Pulse trains are obtained as pumped by a 785nm laser diode.The maximum average output power is 1.27W.Peak power up to 4.2kW and pulse energy up to 840μJ are obtained with the pulse duration of 200ns produced at a repetition rate of 1 kHz.The laser performance is studied under different repetition rates and pump powers.Lastly,we give some discussion.展开更多
Large-scale nanowires are grown on Si wafers by the catalyst-free one-step thermal reaction method in Ar/H_(2) mixture atmosphere at 1000°C.The x−ray diffraction and energy dispersive x-ray spectroscopy results r...Large-scale nanowires are grown on Si wafers by the catalyst-free one-step thermal reaction method in Ar/H_(2) mixture atmosphere at 1000°C.The x−ray diffraction and energy dispersive x-ray spectroscopy results reveal that the final nanowires are of silicon nanostructures.The field emission scanning electron microscopy shows that these self-organized Si nanowires(SiNWs)possess curly crowns with diameters varying from 10 to 300 nm and lengths of up to several hundreds of micrometers.The transmission electron microscopy indicates that the nanowires are pure Si with amorphous structures.All the measurement results show that no silicon oxide is generated in our products.The growth mechanism is proposed tentatively.Silicon oxide is reduced into Si nanoparticles under the Ar/H_(2) mixture,which is the main reason for the formation of such SiNWs.Our experiments offer a method of preparing Si nanostructures by simply reducing silicon oxide at high temperature.展开更多
We demonstrate an erbium-doped ring-cavity fiber laser Q-switched by a graphene oxide-based saturable absorber(GOSA).The GOSA was fabricated by vertically evaporating GO-polyvinylalcohol(GO/PVA)composite dispersion,an...We demonstrate an erbium-doped ring-cavity fiber laser Q-switched by a graphene oxide-based saturable absorber(GOSA).The GOSA was fabricated by vertically evaporating GO-polyvinylalcohol(GO/PVA)composite dispersion,and has a good performance under room temperature.Utilizing a specially fabricated fiber Bragg grating(FBG),stable five-wavelength lasing is realized and stabilized at different pump powers under any polarization.When the pump power increases from 78.4 mW to 379.3 mW,the output power ranging from 1.9 mW to 16.6 mW could be obtained,with pulse duration from 6.8μs to 2.72μs,single pulse energy from 123.73 nJ to 229.74 nJ,and pulse repetition rate from 15.36 kHz to 72.25 kHz.To the best of our knowledge,it is the first simultaneous realization of five-wavelength operation and pulse output in a GO Q-switched all fiber laser system.展开更多
Millimeter wave technology is one of the technologies developed rapidly in recent years. The research was mainly to study the transmission of millimeter wave through textile material named silk fabric. We observed the...Millimeter wave technology is one of the technologies developed rapidly in recent years. The research was mainly to study the transmission of millimeter wave through textile material named silk fabric. We observed the phenomenon of sub-millimeter-wave transmission and reflection of the silk fabric, and concluded that with the number of silk fabric layers increasing, effect of scattering and absorption of the millimeter wave enhanced. The conclusion could be further employed in millimeter wave and THz imaging, dangerous goods inspection and other security application.展开更多
We report on a mid-infrared fiber laser that uses a single-walled carbon nanotube saturable absorber mirror to realize the mode-locking operation.The laser generates 3.5 μm ultra-short pulses from an erbium-doped flu...We report on a mid-infrared fiber laser that uses a single-walled carbon nanotube saturable absorber mirror to realize the mode-locking operation.The laser generates 3.5 μm ultra-short pulses from an erbium-doped fluoride fiber by utilizing a dual-wavelength pumping scheme.Stable mode-locking is achieved at the 3.5 μm band with a repetition rate of 25.2 MHz.The maximum average power acquired from the laser in the mode-locking regime is 25 mW.The experimental results indicate that the carbon nanotube is an effective saturable absorber for mode-locking in the mid-infrared spectral region.展开更多
Temporal and spatial resonant modes are always possessed in physical systems with energy oscillation.In ultrafast fiber lasers,enormous progress has been made toward controlling the interactions of many longitudinal m...Temporal and spatial resonant modes are always possessed in physical systems with energy oscillation.In ultrafast fiber lasers,enormous progress has been made toward controlling the interactions of many longitudinal modes,which results in temporally mode-locked pulses.Recently,optical vortex beams have been extensively investigated due to their quantized orbital angular momentum,spatially donut-like intensity,and spiral phase front.In this paper,we have demonstrated the first to our knowledge observation of optical vortex mode switching and their corresponding pulse evolution dynamics in a narrow-linewidth mode-locked fiber laser.The spatial mode switching is achieved by incorporating a dual-resonant acousto-optic mode converter in the vortex mode-locked fiber laser.The vortex mode-switching dynamics have four stages,including quiet-down,relaxation oscillation,quasi mode-locking,and energy recovery prior to the stable mode-locking of another vortex mode.The evolution dynamics of the wavelength shifting during the switching process are observed via the time-stretch dispersion Fourier transform method.The spatial mode competition through optical nonlinearity induces energy fluctuation on the time scale of ultrashort pulses,which plays an essential role in the mode-switching dynamic process.The results have great implications in the study of spatial mode-locking mechanisms and ultrashort laser applications.展开更多
基金Supported by the National Key R&D Program of China under Grant No 2016YFA0401100the National Natural Science Foundation of China under Grant No 61575129the National High-Technology Research and Development Program of China under Grant No 2015AA021102
文摘In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four metals with distinctly different thermal conductivities, i.e., titanium, nickel, molybdenum, and copper, are selected as light absorbers. The lap welding is conducted with an 808 nm diode laser and simulation experiments are also conducted. Nickel electroplating test is carried out to minimize the side-effects from different light absorptivities of different metals. The results show that the welding with an absorber of higher thermal conductivity can accommodate higher laser input power before smoking, which produces a wider and stronger welding seam.The positive role of the higher thermal conductivity can be attributed to the fact that a desirable thermal field distribution for the molecular diffusion and entanglement is produced from the case with a high thermal conductivity.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61275144 and 61308049, the PhD Start-up Fund of Natural Science Foundation of Guangdong Province under Grant No $2013040012496, the Science and Technology Project of Shenzhen City under Grant Nos JCYJ20120613110637373 and JCYJ20130329142022715, the Improvement and Development Project of Shenzhen Key Lab under Grant No ZDSY20120612094924467, and the Natural Science Foundation of Shenzhen University under Grant No 201203.
文摘We numerically investigate the seven-core photonic crystal fiber (PCF) with the zero dispersion wavelength designed in the range of 1000 - 1080 nm, particularly suitable for the ytterbium-doped fiber laser pumping. Also, the PCFs are well designed for obtaining a flat in-phase mode by carefully adjusting the diameter of inner layer six holes, and the corresponding empirical values of fiber structure are summarized and listed. The variations of inner six holes to the amplitude of in-phase mode are further investigated, and our results show that a better tolerance can be achieved in the fiber structures with lower filling ratio configuration.
基金Supported by the National Natural Science Foundation of China under No 60471048, and the Shenzhen Science and Technology Bureau under Grant No 200617.
基金Supported by the National Natural Science Foundation of China under Grant No 10804074, the Key Natural Science Research Project of Guangdong Higher Education Institutions （No 05Z019）, the Science and Technology Project of Shenzhen （No 200718）, the Key Laboratory Upgrading and Developing Project.
基金the support of National Natural Science Foundation of China (Nos. 51702284 and 21878270)Zhejiang Provincial Natural Science Foundation of China (LR19B060002)+5 种基金the Startup Foundation for Hundred-Talent Program of Zhejiang University(112100-193820101/001/022)the support of Shenzhen Science and Technology Project of China (JCYJ20170412105400428)the support of Zhejiang Provincial Natural Science Foundation of China (LR16F040001)Open Project of Laboratory for Biomedical Engineering of Ministry of Education, Zhejiang Universitythe support of Innovation Platform of Energy Storage Engineering and New Material in Zhejiang University (K19-534202-002)Provincial Innovation Team on Hydrogen Electric Hybrid Power Systems in Zhejiang Province
文摘An integrated system has been provided with a-Si/H solar cells as energy conversion device,NiCo2O4 battery-supercapacitor hybrid(BSH)as energy storage device,and light emitting diodes(LEDs)as energy utilization device.By designing three-dimensional hierarchical NiCo2O4 arrays as faradic electrode,with capacitive electrode of active carbon(AC),BSHs were assembled with energy density of 16.6 Wh kg-1,power density of 7285 W kg-1,long-term stability with 100% retention after 15,000 cycles,and rather low self-discharge.The NiCo2O4//AC BSH was charged to 1.6 V in 1 s by solar cells and acted as reliable sources for powering LEDs.The integrated system is rational for operation,having an overall efficiency of 8.1% with storage efficiency of 74.24%.The integrated system demonstrates a stable solar power conversion,outstanding energy storage behavior,and reliable light emitting.Our study offers a precious strategy to design a self-driven integrated system for highly efficient energy utilization.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61275144 and 61308049, the PhD Start-up Fund of Natural Science Foundation of Guangdong Province under Grant Nos S2012040007242 and S2013040012496, the Science and Technology Project of Shenzhen City under Grant Nos JCYJ20120613110637373, JCYJ20130329142022715 and JC201105170655A, the Improvement and Development Project of Shenzhen Key Lab under Grant No ZDSY20120612094924467, and the Natural Science Foundation of Shenzhen University under Grant No 201203.
基金Project supported by the Postdoctoral Science Foundation of China(Grant Nos.2016M592528 and 2016M602517)the Natural Science Foundation of Guangdong Province,China(Grant No.2017A030310130)the National Natural Science Foundation of China(Grant No.11705259)
文摘The design, fabrication and performance of narrow-band rugate minus filters are investigated in this paper. A method of fabricating graded-index coatings by rapidly alternating deposition of low(Si O2) and high(Al2 O3) refractive index materials is presented to fabricate a rugate structure. The narrow-band rugate minus filter design and fabrication approaches are discussed in detail. The experimental results, including transmittance spectrum, surface damage test and damage morphology investigated with a scanning electron microscope, demonstrate the high performance of the as-fabricated spatial filter and confirm the feasibility of the fabrication method for narrow-band rugate minus filters.
基金Supported by the Science and Technology Project of Shenzhen under Grant Nos JCYJ20140509172609175 and JSGG20140519104809878the Science and Technology Project of Guangdong Province under Grant No 2014B010131006
文摘We present a high power diode-pumped continuous-wave Tm:YLF(Tm^(3+)-doped lithium yttrium fluoride) laser with a piece of silicon wafer as the output coupler(Si-OC laser) directly.Under the pump power of 40 W at 793 nm,a maximum output power of 12.1 W is obtained with a beam quality of M^2 ≤ 1.55 at 1887 nm,corresponding to an optical-to-optical efficiency of 30.25%and a slope efficiency of 33.21%.To the best of our knowledge,this is the first report on directly utilizing silicon as an output coupler(Si-OC) in the solid Tm:YLF laser system.Due to the intriguing characteristics of silicon,such as negligible absorption in the wavelength region around 2 μm,high damage threshold,low cost and long-pass filter properties,double-side polished monocrystalline silicon wafer is considered as an outstanding candidate output coupler in the high-power laser system 2 μm spectral region,which may dramatically reduce the total manufacturing costs of the 2 μm laser system.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61775146,11704260,61405126,and 61605122)the Shenzhen Science and Technology Project(Grant Nos.JCYJ20160427105041864,JSGG20160429114438287,KQJSCX20160226194031,JCYJ20160422103744090,and JCY20150324141711695)the Natural Science Foundation of Guangdong Province,China(Grant Nos.2016A030310049,2016A030310059,and2017A030310402)
文摘Ultrafast pulse generation was demonstrated in thulium doped fiber laser mode locked by magnetron sputtering deposited Sb_2Te_3with the modulation depth,non-saturable loss,and saturable intensity of 38%,31.2%,and 3.3 MW/cm^2,respectively.Stable soliton pulses emitting at 1930.07 nm were obtained with pulse duration of 1.24 ps,a 3-dB spectral bandwidth of 3.87 nm,an average output power of 130 m W,and signal-to-noise ratio(SNR)of 84 dB.To our knowledge,this is the first demonstration of Sb_2Te_3-based SA in fiber lasers at 2-μm regime.
基金Supported in part by the Double Hundred Project of Shenzhen under Grant No 001096.
文摘A switchable multi-wavelength erbium-doped photonic crystal fiber laser with a linear cavity configuration based on a Sagnac loop mirror is proposed and demonstrated experimentally.The laser is based on saturated spectral hole burning and the polarization hole burning effects can be switched among single-wavelength,dual-wavelength,triple-wavelength and quadruple-wavelength outputs at room temperature.The wavelength period of the output spectrum is easily varied by using polarization maintaining fibers of different lengths.The proposed fiber laser has a signal-to-noise ratio of higher than 30 dB and achieves a low threshold power of 37 mW.The power fluctuations of the lasing lines are less than 0.54 dB,1.7 dB and 2.9 dB when the laser operates at single-wavelength,dual-wavelength and triple-wavelength for one hour.
基金Supported by the National Natural Science Foundation of China under Grant No 61007054the Natural Science Foundation of Guangdong Province(9451806001002428)the Science and Technology Project of Shenzhen City(200716).
文摘We report a cladding-pumped Tm^(3+)-doped domestic silica fiber laser operated at 2pm and actively Q-switched with an acousto-optic modulator.Pulse trains are obtained as pumped by a 785nm laser diode.The maximum average output power is 1.27W.Peak power up to 4.2kW and pulse energy up to 840μJ are obtained with the pulse duration of 200ns produced at a repetition rate of 1 kHz.The laser performance is studied under different repetition rates and pump powers.Lastly,we give some discussion.
基金Supported by the China Postdoctoral Fund under Grant No.20100470902the Shenzhen Natural Science Foundation of China Under Grant No.JC200903120019A.
文摘Large-scale nanowires are grown on Si wafers by the catalyst-free one-step thermal reaction method in Ar/H_(2) mixture atmosphere at 1000°C.The x−ray diffraction and energy dispersive x-ray spectroscopy results reveal that the final nanowires are of silicon nanostructures.The field emission scanning electron microscopy shows that these self-organized Si nanowires(SiNWs)possess curly crowns with diameters varying from 10 to 300 nm and lengths of up to several hundreds of micrometers.The transmission electron microscopy indicates that the nanowires are pure Si with amorphous structures.All the measurement results show that no silicon oxide is generated in our products.The growth mechanism is proposed tentatively.Silicon oxide is reduced into Si nanoparticles under the Ar/H_(2) mixture,which is the main reason for the formation of such SiNWs.Our experiments offer a method of preparing Si nanostructures by simply reducing silicon oxide at high temperature.
基金Supported by the National Key Basic Research and Development Program of China(No 2010CB735904)NSFC(No 61007054)+5 种基金Doctoral Program of High School Research Fund(No 20104408110002)the Improvement and Development Project of Shenzhen Key Lab(No CXB201005240014A)the Science and Technology Project of Shenzhen City(No JC201105170693A)the Key Program of Basic Research Project of Shenzhen(No JC201005250048A)the Applied Technology Developmental Project of Shenzhen University(No 201221)the Research Grants Council of Hong Kong,China(No GRF PolyU 526511).
文摘We demonstrate an erbium-doped ring-cavity fiber laser Q-switched by a graphene oxide-based saturable absorber(GOSA).The GOSA was fabricated by vertically evaporating GO-polyvinylalcohol(GO/PVA)composite dispersion,and has a good performance under room temperature.Utilizing a specially fabricated fiber Bragg grating(FBG),stable five-wavelength lasing is realized and stabilized at different pump powers under any polarization.When the pump power increases from 78.4 mW to 379.3 mW,the output power ranging from 1.9 mW to 16.6 mW could be obtained,with pulse duration from 6.8μs to 2.72μs,single pulse energy from 123.73 nJ to 229.74 nJ,and pulse repetition rate from 15.36 kHz to 72.25 kHz.To the best of our knowledge,it is the first simultaneous realization of five-wavelength operation and pulse output in a GO Q-switched all fiber laser system.
文摘Millimeter wave technology is one of the technologies developed rapidly in recent years. The research was mainly to study the transmission of millimeter wave through textile material named silk fabric. We observed the phenomenon of sub-millimeter-wave transmission and reflection of the silk fabric, and concluded that with the number of silk fabric layers increasing, effect of scattering and absorption of the millimeter wave enhanced. The conclusion could be further employed in millimeter wave and THz imaging, dangerous goods inspection and other security application.
基金supported by the National Natural Science Foundation of China (NSFC) (Nos. 61975136, 61935014, 61775146, and 61905151)Guangdong Basic and Applied Basic Research Foundation (No. 2019A1515010699)+2 种基金Shenzhen Science and Technology Project (Nos. JCYJ20160520161351540, JCYJ20170817100639177,JCYJ20170302151146995, JCYJ20180305125352956,JCYJ20160328144942069,and JCYJ20190808141011530)State Key Laboratory of Information Photonics and Optical Communications (No. IPOC2019ZZ01)State Key Laboratory of Pulsed Power Laser Technology (No. SKL2018KF04)
文摘We report on a mid-infrared fiber laser that uses a single-walled carbon nanotube saturable absorber mirror to realize the mode-locking operation.The laser generates 3.5 μm ultra-short pulses from an erbium-doped fluoride fiber by utilizing a dual-wavelength pumping scheme.Stable mode-locking is achieved at the 3.5 μm band with a repetition rate of 25.2 MHz.The maximum average power acquired from the laser in the mode-locking regime is 25 mW.The experimental results indicate that the carbon nanotube is an effective saturable absorber for mode-locking in the mid-infrared spectral region.
基金National Key Research and Development Program of China(2018YFB1801800)National Natural Science Foundation of China(91750108,61635006)111 Project(D20031)。
文摘Temporal and spatial resonant modes are always possessed in physical systems with energy oscillation.In ultrafast fiber lasers,enormous progress has been made toward controlling the interactions of many longitudinal modes,which results in temporally mode-locked pulses.Recently,optical vortex beams have been extensively investigated due to their quantized orbital angular momentum,spatially donut-like intensity,and spiral phase front.In this paper,we have demonstrated the first to our knowledge observation of optical vortex mode switching and their corresponding pulse evolution dynamics in a narrow-linewidth mode-locked fiber laser.The spatial mode switching is achieved by incorporating a dual-resonant acousto-optic mode converter in the vortex mode-locked fiber laser.The vortex mode-switching dynamics have four stages,including quiet-down,relaxation oscillation,quasi mode-locking,and energy recovery prior to the stable mode-locking of another vortex mode.The evolution dynamics of the wavelength shifting during the switching process are observed via the time-stretch dispersion Fourier transform method.The spatial mode competition through optical nonlinearity induces energy fluctuation on the time scale of ultrashort pulses,which plays an essential role in the mode-switching dynamic process.The results have great implications in the study of spatial mode-locking mechanisms and ultrashort laser applications.
