X-ray free-electron lasers(XFELs)can generate bright X-ray pulses with short durations and narrow bandwidths,leading to extensive applica-tions in many disciplines such as biology,materials science,and ultrafast scien...X-ray free-electron lasers(XFELs)can generate bright X-ray pulses with short durations and narrow bandwidths,leading to extensive applica-tions in many disciplines such as biology,materials science,and ultrafast science.Recently,there has been a growing demand for X-ray pulses with high photon energy,especially from developments in“diffraction-before-destruction”applications and in dynamic mesoscale materials science.Here,we propose utilizing the electron beams at XFELs to drive a meter-scale two-bunch plasma wakefield accelerator and double the energy of the accelerated beam in a compact and inexpensive way.Particle-in-cell simulations are performed to study the beam quality degradation under different beam loading scenarios and nonideal issues,and the results show that more than half of the accelerated beam can meet the requirements of XFELs.After its transport to the undulator,the accelerated beam can improve the photon energy to 22 keV by a factor of around four while maintaining the peak power,thus offering a promising pathway toward high-photon-energy XFELs.展开更多
In long-cavity edge-emitting diode lasers,longitudinal spatial hole burning(LSHB),two-photon ab⁃sorption(TPA)and free carrier absorption(FCA)are among the key factors that affect the linear increase in out⁃put power a...In long-cavity edge-emitting diode lasers,longitudinal spatial hole burning(LSHB),two-photon ab⁃sorption(TPA)and free carrier absorption(FCA)are among the key factors that affect the linear increase in out⁃put power at high injection currents.In this paper,a simplified numerical analysis model is proposed for 1.06μm long-cavity diode lasers by combining TPA and FCA losses with one-dimensional(1D)rate equations.The ef⁃fects of LSHB,TPA and FCA on the output characteristics are systematically analyzed,and it is proposed that ad⁃justing the front facet reflectivity and the position of the quantum well(QW)in the waveguide layer can improve the front facet output power.展开更多
Compressing all the energy of a laser pulse into a spatiotemporal focal cube edged by the laser center wavelength will realize the highest intensity of an ultra-intense ultrashort laser,which is called theλ^(3) regim...Compressing all the energy of a laser pulse into a spatiotemporal focal cube edged by the laser center wavelength will realize the highest intensity of an ultra-intense ultrashort laser,which is called theλ^(3) regime or theλ^(3) laser.Herein,we introduced a rotational hyperbolic mirror—an important rotational conic section mirror with two foci—that is used as a secondary focusing mirror after a rotational parabolic mirror to reduce the focal spot size from several wavelengths to a single wavelength by significantly increasing the focusing angular aperture.Compared with the rotational ellipsoidal mirror,the first focal spot with a high intensity,as well as some unwanted strong-field effects,is avoided.The optimal focusing condition of this method is presented and the enhanced tight focusing for a femtosecond petawatt laser and theλ3 laser is numerically simulated,which can enhance the focused intensities of ultra-intense ultrashort lasers for laser physics.展开更多
The discovery of chirped pulse amplification has led to great improvements in laser technology,enabling energetic laser beams to be compressed to pulse durations of tens of femtoseconds and focused to a few micrometer...The discovery of chirped pulse amplification has led to great improvements in laser technology,enabling energetic laser beams to be compressed to pulse durations of tens of femtoseconds and focused to a few micrometers.Protons with energies of tens of MeV can be accelerated using,for instance,target normal sheath acceleration and focused on secondary targets.Under such conditions,nuclear reactions can occur,with the production of radioisotopes suitable for medical application.The use of high-repetition lasers to produce such isotopes is competitive with conventional methods mostly based on accelerators.In this paper,we study the production of^(67)Cu,^(63)Zn,^(18)F,and^(11)C,which are currently used in positron emission tomography and other applications.At the same time,we study the reactions^(10)B(p,α)^(7)Be and^(70)Zn(p,4n)^(67)Ga to put further constraints on the proton distributions at different angles,as well as the reaction^(11)B(p,α)^(8)Be relevant for energy production.The experiment was performed at the 1 PW laser facility at VegaⅢin Salamanca,Spain.Angular distributions of radioisotopes in the forward(with respect to the laser direction)and backward directions were measured using a high purity germanium detector.Our results are in reasonable agreement with numerical estimates obtained following the approach of Kimura and Bonasera[Nucl.Instrum.Methods Phys.Res.,Sect.A 637,164–170(2011)].展开更多
Ultrashort and powerful laser interactions with a target generate intense wideband electromagnetic pulses(EMPs).In this study,we report EMPs generated by the interactions between petawatt(30 fs,1.4×10^(20) W/cm^(...Ultrashort and powerful laser interactions with a target generate intense wideband electromagnetic pulses(EMPs).In this study,we report EMPs generated by the interactions between petawatt(30 fs,1.4×10^(20) W/cm^(2))femtosecond(fs)lasers with metal flat,plastic flat,and plastic nanowire-array(NWA)targets.Detailed analyses are conducted on the EMPs in terms of their spatial distribution,time and frequency domains,radiation energy,and protection.The results indicate that EMPs from metal targets exhibit larger amplitudes at varying angles than those generated by other types of targets and are enhanced significantly for NWA targets.Using a plastic target holder and increasing the laser focal spot can significantly decrease the radiation energy of the EMPs.Moreover,the composite shielding materials indicate an effective shielding effect against EMPs.The simulation results show that the NWA targets exert a collimating effect on thermal electrons,which directly affects the distribution of EMPs.This study provides guidance for regulating EMPs by controlling the laser focal spot,target parameters,and target rod material and is beneficial for electromagnetic-shielding design.展开更多
Realizing the full potential of ultrahigh-intensity lasers for particle and radiation generation will require multi-beam arrangements due to technology limitations.Here,we investigate how to optimize their coupling wi...Realizing the full potential of ultrahigh-intensity lasers for particle and radiation generation will require multi-beam arrangements due to technology limitations.Here,we investigate how to optimize their coupling with solid targets.Experimentally,we show that overlapping two intense lasers in a mirror-like configuration onto a solid with a large preplasma can greatly improve the generation of hot electrons at the target front and ion acceleration at the target backside.The underlying mechanisms are analyzed through multidimensional particle-in-cell simulations,revealing that the self-induced magnetic fields driven by the two laser beams at the target front are susceptible to reconnection,which is one possible mechanism to boost electron energization.In addition,the resistive magnetic field generated during the transport of the hot electrons in the target bulk tends to improve their collimation.Our simulations also indicate that such effects can be further enhanced by overlapping more than two laser beams.展开更多
Passively mode-locked fiber lasers emit femtosecond pulse trains with excellent short-term stability. The quantum-limited timing jitter of a free running femtosecond erbium-doped fiber laser working at room temperatur...Passively mode-locked fiber lasers emit femtosecond pulse trains with excellent short-term stability. The quantum-limited timing jitter of a free running femtosecond erbium-doped fiber laser working at room temperature is considerably below one femtosecond at high Fourier frequency. The ultrashort pulse train with ultralow timing jitter enables absolute time-of-flight measurements based on a dual-comb implementation, which is typically composed of a pair of optical frequency combs generated by femtosecond lasers. Dead-zone-free absolute distance measurement with sub-micrometer precision and kHz update rate has been routinely achieved with a dual-comb configuration, which is promising for a number of precision manufacturing applications, from large step-structure measurements prevalent in microelectronic profilometry to three coordinate measurements in large-scale aerospace manufacturing and shipbuilding. In this paper, we first review the sub-femtosecond precision timing jitter characterization methods and approaches for ultralow timing jitter mode-locked fiber laser design. Then, we provide an overview of the state-of-the-art dual-comb absolute ranging technology in terms of working principles, experimental implementations, and measurement precisions. Finally, we discuss the impact of quantum-limited timing jitter on the dual-comb ranging precision at a high update rate. The route to highprecision dual-comb range finder design based on ultralow jitter femtosecond fiber lasers is proposed.展开更多
By employing three reflecting volume Bragg gratings, a near-infrared 4-channel spectral-beam-combining system is demonstrated to present 720 W combined power with a combining efficiency of 94.7%. The combined laser be...By employing three reflecting volume Bragg gratings, a near-infrared 4-channel spectral-beam-combining system is demonstrated to present 720 W combined power with a combining efficiency of 94.7%. The combined laser beam is near-diffraction-limited with a beam factor M^2-1.54. During this 4-channel beam-combining process, no special active cooling measures are used to evaluate the volume Bragg gratings as combining elements are under the higher power laser operation. Thermal expansion and period distortion are verified in a 2 k W 2-channel beam-combining process, and the heat issue in the transmission case is found to be more remarkable than that in the diffraction e-se. Transmitted and diffracted beams experience wave-front aberrations with different degrees, thus leading to distinct beam deterioration.展开更多
INTRODUCTIONEndoscopy has revolutionised our management of many gastrointestinal disorders over the past 30 years .We are increasingly able to diagnose gastrointestinal (GI) tumors at an early stage,and endoscopic the...INTRODUCTIONEndoscopy has revolutionised our management of many gastrointestinal disorders over the past 30 years .We are increasingly able to diagnose gastrointestinal (GI) tumors at an early stage,and endoscopic therapy has made a difference to the outcome of GI haemorrhage. We still rely on surgery for cure of cancer of cancer but as diagnostic techniques improve the goal of minimally invasive diagnosis and therapy appears ever more attainable diagnosis and therapy appears vevr more attainable . As populations get older ,it is also increasingly desirable .Laser light can be used for both diagnosis and therapy in the gut .This article reviews the value of lasers in these areas .展开更多
Laser polishing is widely employed to reduce the surface roughness of products with complex geometries.Traditional laser polishing techniques use a single high-power Gaussian beam to melt and smooth a thin layer of su...Laser polishing is widely employed to reduce the surface roughness of products with complex geometries.Traditional laser polishing techniques use a single high-power Gaussian beam to melt and smooth a thin layer of surface material.However,the reliance on high power lasers can present practical challenges such as minimizing surface evaporation or reducing overall cost.In this work,we combined two identical low-power laser beams with a spatial offset in between them to construct an elliptical beam.By changing the spatial offset,combined beams with different lengths along the major axis can be created.We observe over 20%improvement in line roughness reduction using this approach compared to a single Gaussian laser beam with the same total power.Additionally,both experiment and simulation results suggest such improvement is because this dual-laser set-up can create a longer molten pool compared to a single laser.展开更多
A 1040 nm tapered laser with tapered distributed Bragg reflector(DBR) grating is designed and fabricated. By designing the grating with tapered layout, the tapered DBR grating exhibits the scattering effect on side ba...A 1040 nm tapered laser with tapered distributed Bragg reflector(DBR) grating is designed and fabricated. By designing the grating with tapered layout, the tapered DBR grating exhibits the scattering effect on side backward-traveling waves, thus achieving additional suppression of parasitic oscillation. Under the suppression of parasitic oscillation, the spatial and spectral characteristics of the tapered laser are improved. The experimental results show that a near-Gaussian far-field distribution and a kink-free P–I characteristics are achieved, and a single peak emission with a wavelength of1046.84 nm and a linewidth of 56 pm is obtained.展开更多
We propose a method to directly measure phase-related noise characteristics of single-frequency lasers in the 728–980 nm band based on a 120°phase difference interferometer.Differential phase information of the ...We propose a method to directly measure phase-related noise characteristics of single-frequency lasers in the 728–980 nm band based on a 120°phase difference interferometer.Differential phase information of the laser under test is demodulated via the interferometer.Other parameters related to the phase noise characteristics such as linewidth at different observation time, phase/frequency noise, power spectrum density of phase/frequency fluctuation, and Allan deviation are further obtained.Frequency noise as low as 1 Hz^2/Hz can be measured using our system.Then the phase-related noise characteristics of two commercial lasers frequently used in cold atomic clocks are studied systematically by the method.Furthermore, several influencing factors and their relative evolution laws are also revealed, such as the pump current and frequency-locking control parameters.This would help to optimize the laser performance, select laser sources, and evaluate the system performance for cold atomic physics applications.展开更多
InG sP/G s SCH SQW lasers have been prepared by LP-MOCVD. The dependence of t hreshold current density on cavity length was explained. Laser diodes are char acterized by the output power of 1 W to 2 W, threshold curre...InG sP/G s SCH SQW lasers have been prepared by LP-MOCVD. The dependence of t hreshold current density on cavity length was explained. Laser diodes are char acterized by the output power of 1 W to 2 W, threshold current density ( J th ) of 330 A/cm 2 to 450 A/cm 2 and external differe ntial quantum efficiency ( η d) of 35% to 75%, and these characteristics ar e in good agreement with the designed requirement.展开更多
We present a cascaded nonlinear spectral broadening scheme for Nd-doped lasers,featuring with long pulse duration and high average power.This scheme is based on two multi-pass cells(MPCs)and one multiple-plate superco...We present a cascaded nonlinear spectral broadening scheme for Nd-doped lasers,featuring with long pulse duration and high average power.This scheme is based on two multi-pass cells(MPCs)and one multiple-plate supercontinuum generation(MPSG),and the numerical investigation is driven by a home-made Nd-doped fiber laser with 12 ps pulse duration,50 kHz repetition rate and 100 W average power.The MPC-based first two stages allow us to broaden the pulse spectrum to 4 nm and 43 nm respectively,and subsequently,the MPSG-based third stage allows us to reach 235 nm spectral bandwidth.This broadened spectrum can support a Fourier-transfer-limited pulse duration of 9.8 fs,which is shorter than three optical cycles.To the best of our knowledge,it is the first time to demonstrate the possibility of few-cycle pulses generation based on the 10 ps level Nd-doped lasers.Such few-cycle and high average power laser sources should be attractive and prospective,benefiting from the characteristics of structure compact,low-cost and flexibility.展开更多
We report on the measurement of junction temperature of the InAs/InP（l00） quantum dot lasers working in the 1.55μm wavelength region. The measurement is based on analyzing the temperature induced mode shift of the ...We report on the measurement of junction temperature of the InAs/InP（l00） quantum dot lasers working in the 1.55μm wavelength region. The measurement is based on analyzing the temperature induced mode shift of the Fabry-Perot cavity. Under pulsed operation mode, more than 20℃ junction temperature rise is measured for the quantum-dot （QD） laser when the duty cycle is increased from 1% to 95%. For a reference quantum well laser, the junction temperature rise is obtained as only around 3℃. The large junction temperature rise might be a crucial factor to improve the performance of QD lasers.展开更多
We have carried out the hohlraum experiments about radiation temperature scaling on the Shenguang-Ⅱ （SG- Ⅱ） laser facility with eight laser beams of 0.35#m, pulse duration of about 1.0ns and total energy of 2000J....We have carried out the hohlraum experiments about radiation temperature scaling on the Shenguang-Ⅱ （SG- Ⅱ） laser facility with eight laser beams of 0.35#m, pulse duration of about 1.0ns and total energy of 2000J. The reradiated x-ray flux through the laser entrance hole was measured using a soft x-ray spectrometer. The measured peak radiation temperature was 170eV for the standard hohlraum and 150 eV for the 1.5-scaled one. We have derived the radiation temperature scaling law, in which the laser hohlraum coupling efficiency is included. With an appropriate coupling efficiency, the coincidences between experimental and scaling hohlraum radiation temperatures are rather good.展开更多
We report on a theoretical and experimental study of an all-normal-dispersion （ANDi） Yb-doped mode-locked fiber laser, in which nonlinear polarization rotation （NPR） is used to realize mode-locking without any dis...We report on a theoretical and experimental study of an all-normal-dispersion （ANDi） Yb-doped mode-locked fiber laser, in which nonlinear polarization rotation （NPR） is used to realize mode-locking without any dispersion compensation. Based on the coupled nonlinear Schr6dinger （CNLS） equation, a model simulating the mode-locked process of an all-normal-dispersion ring fiber laser is developed, which shows that the achievement of stable mode-locking depends on the alignment of the polarization controller （PC） along the fast-polarization axis of the fiber, the birefringence intensity, and the net cavity dispersion. According to the theoretical analysis, stable mode-locked pulses with pulse duration 300 ps and average output power 33.9 mW at repetition rate 36 MHz are obtained.展开更多
Continuous-wave chemical oxygen-iodine lasers (COILs) can be operated in a pulsed operation mode to obtain a higher peak power.The key point is to obtain a uniform and stable glow discharge in the mixture of singlet d...Continuous-wave chemical oxygen-iodine lasers (COILs) can be operated in a pulsed operation mode to obtain a higher peak power.The key point is to obtain a uniform and stable glow discharge in the mixture of singlet delta oxygen and iodide.We propose using an electrode system with the assistance of surface sliding pre-ionization to solve the problem of the stable glow discharge with a large aperture.The pre-ionization unit is symmetrically fixed on the plane of the cathode surface.A uniform and stable glow discharge is obtained in a mixture of iodide (such as CH3I) and nitrogen at the specific deposition energy of 4.5 J/L,pressure of 1.99-3.32 kPa,aperture size of 11 cm × 10cm.The electrode system is applied in a pulsed COIL.Laser energy up to 4.4J is obtained and the specific energy output is 2 J/L.展开更多
Passively Q-switched quasi-continuous-wave （QCW） diode-pumped Nd：YAG laser with Cr^4＋ ：YAG as saturable absorber is numerically investigated by solving the coupled rate equations. The threshold pump rate for pass...Passively Q-switched quasi-continuous-wave （QCW） diode-pumped Nd：YAG laser with Cr^4＋ ：YAG as saturable absorber is numerically investigated by solving the coupled rate equations. The threshold pump rate for passively Q-switched QCW-pumped laser is derived. The effects of the pump rate and pump-pulse duration on the laser operation characteristics are studied theoretically. The pump power range can be estimated according to the number of output pulses. The numerical simulation results are in good agreement with the experimental results.展开更多
We study a femtosecond Ti：sapphire laser pumped optical parametric amplifier （OPA） at 1053nm. The OPA Generates stable signal pulses with duration smaller than l OOfs, wavelength drift smaller than 0.5 nm, and puls...We study a femtosecond Ti：sapphire laser pumped optical parametric amplifier （OPA） at 1053nm. The OPA Generates stable signal pulses with duration smaller than l OOfs, wavelength drift smaller than 0.5 nm, and pulseto-pulse fluctuation of about ±4%, by employinG an external seeder. In a terawatt laser pumped large-aperture LiNbOa OPA, pulse energy at signal has been scaled up to 4mJ. This m J-class femtosecond OPA at 1053nm presents a feasible alternative to optical parametric chirped-pulse amplification, and is ready to be applied to petawatt lasers.展开更多
基金supported by the National Grand Instrument Project No. SQ2019YFF01014400the Natural Science Foundation of China (Grant Nos. 12375147, 12435011, 12075030)+2 种基金the Beijing Outstanding Young Scientist Project, Project for Young Scientists in Basic Research of Chinese Academy of Sciences (YSBR-115)the Beijing Normal University Scientific Research Initiation Fund for Introducing Talents No. 310432104the Fundamental Research Funds for the Central Universities, Peking University
文摘X-ray free-electron lasers(XFELs)can generate bright X-ray pulses with short durations and narrow bandwidths,leading to extensive applica-tions in many disciplines such as biology,materials science,and ultrafast science.Recently,there has been a growing demand for X-ray pulses with high photon energy,especially from developments in“diffraction-before-destruction”applications and in dynamic mesoscale materials science.Here,we propose utilizing the electron beams at XFELs to drive a meter-scale two-bunch plasma wakefield accelerator and double the energy of the accelerated beam in a compact and inexpensive way.Particle-in-cell simulations are performed to study the beam quality degradation under different beam loading scenarios and nonideal issues,and the results show that more than half of the accelerated beam can meet the requirements of XFELs.After its transport to the undulator,the accelerated beam can improve the photon energy to 22 keV by a factor of around four while maintaining the peak power,thus offering a promising pathway toward high-photon-energy XFELs.
基金Supported by National Key R&D Project(2017YFB0405100)National Natural Science Foundation of China(61774024/61964007)Jilin province science and technology development plan(20190302007GX)。
文摘In long-cavity edge-emitting diode lasers,longitudinal spatial hole burning(LSHB),two-photon ab⁃sorption(TPA)and free carrier absorption(FCA)are among the key factors that affect the linear increase in out⁃put power at high injection currents.In this paper,a simplified numerical analysis model is proposed for 1.06μm long-cavity diode lasers by combining TPA and FCA losses with one-dimensional(1D)rate equations.The ef⁃fects of LSHB,TPA and FCA on the output characteristics are systematically analyzed,and it is proposed that ad⁃justing the front facet reflectivity and the position of the quantum well(QW)in the waveguide layer can improve the front facet output power.
基金supported by the National Key R&D Program of China(Grant No.2022YFA1604401)the Shanghai Science and Technology Committee Program(Grant Nos.22560780100 and 23560750200)the National Natural Science Foundation of China(Grant No.61925507)。
文摘Compressing all the energy of a laser pulse into a spatiotemporal focal cube edged by the laser center wavelength will realize the highest intensity of an ultra-intense ultrashort laser,which is called theλ^(3) regime or theλ^(3) laser.Herein,we introduced a rotational hyperbolic mirror—an important rotational conic section mirror with two foci—that is used as a secondary focusing mirror after a rotational parabolic mirror to reduce the focal spot size from several wavelengths to a single wavelength by significantly increasing the focusing angular aperture.Compared with the rotational ellipsoidal mirror,the first focal spot with a high intensity,as well as some unwanted strong-field effects,is avoided.The optimal focusing condition of this method is presented and the enhanced tight focusing for a femtosecond petawatt laser and theλ3 laser is numerically simulated,which can enhance the focused intensities of ultra-intense ultrashort lasers for laser physics.
文摘The discovery of chirped pulse amplification has led to great improvements in laser technology,enabling energetic laser beams to be compressed to pulse durations of tens of femtoseconds and focused to a few micrometers.Protons with energies of tens of MeV can be accelerated using,for instance,target normal sheath acceleration and focused on secondary targets.Under such conditions,nuclear reactions can occur,with the production of radioisotopes suitable for medical application.The use of high-repetition lasers to produce such isotopes is competitive with conventional methods mostly based on accelerators.In this paper,we study the production of^(67)Cu,^(63)Zn,^(18)F,and^(11)C,which are currently used in positron emission tomography and other applications.At the same time,we study the reactions^(10)B(p,α)^(7)Be and^(70)Zn(p,4n)^(67)Ga to put further constraints on the proton distributions at different angles,as well as the reaction^(11)B(p,α)^(8)Be relevant for energy production.The experiment was performed at the 1 PW laser facility at VegaⅢin Salamanca,Spain.Angular distributions of radioisotopes in the forward(with respect to the laser direction)and backward directions were measured using a high purity germanium detector.Our results are in reasonable agreement with numerical estimates obtained following the approach of Kimura and Bonasera[Nucl.Instrum.Methods Phys.Res.,Sect.A 637,164–170(2011)].
基金This work was supported by the National Natural Science Foundation of China(Nos.12122501,11975037,61631001,and 11921006)the National Grand Instrument Project(Nos.2019YFF01014400,2019YFF01014404)the Foundation of Science and Technology on Plasma Physics Laboratory(No.6142A04220108).
文摘Ultrashort and powerful laser interactions with a target generate intense wideband electromagnetic pulses(EMPs).In this study,we report EMPs generated by the interactions between petawatt(30 fs,1.4×10^(20) W/cm^(2))femtosecond(fs)lasers with metal flat,plastic flat,and plastic nanowire-array(NWA)targets.Detailed analyses are conducted on the EMPs in terms of their spatial distribution,time and frequency domains,radiation energy,and protection.The results indicate that EMPs from metal targets exhibit larger amplitudes at varying angles than those generated by other types of targets and are enhanced significantly for NWA targets.Using a plastic target holder and increasing the laser focal spot can significantly decrease the radiation energy of the EMPs.Moreover,the composite shielding materials indicate an effective shielding effect against EMPs.The simulation results show that the NWA targets exert a collimating effect on thermal electrons,which directly affects the distribution of EMPs.This study provides guidance for regulating EMPs by controlling the laser focal spot,target parameters,and target rod material and is beneficial for electromagnetic-shielding design.
基金supported by the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation program(Grant Agreement No.787539)funding from EPRSC(Grant Nos.EP/E035728,EP/C003586,and EP/P010059/1)supported by the National Sciences and Engineering Research Council of Canada(NSERC)and Compute Canada(Job:pve-323-ac,PA).
文摘Realizing the full potential of ultrahigh-intensity lasers for particle and radiation generation will require multi-beam arrangements due to technology limitations.Here,we investigate how to optimize their coupling with solid targets.Experimentally,we show that overlapping two intense lasers in a mirror-like configuration onto a solid with a large preplasma can greatly improve the generation of hot electrons at the target front and ion acceleration at the target backside.The underlying mechanisms are analyzed through multidimensional particle-in-cell simulations,revealing that the self-induced magnetic fields driven by the two laser beams at the target front are susceptible to reconnection,which is one possible mechanism to boost electron energization.In addition,the resistive magnetic field generated during the transport of the hot electrons in the target bulk tends to improve their collimation.Our simulations also indicate that such effects can be further enhanced by overlapping more than two laser beams.
基金supported by National Natural Science Foundation of China (Grant Nos.61475162,61675150,and 61535009)Tianjin Natural Science Foundation (Grant No.18JCYBJC16900)Tianjin Research Program of Application Foundation and Advanced Technology (Grant No.17JCJQJC43500)
文摘Passively mode-locked fiber lasers emit femtosecond pulse trains with excellent short-term stability. The quantum-limited timing jitter of a free running femtosecond erbium-doped fiber laser working at room temperature is considerably below one femtosecond at high Fourier frequency. The ultrashort pulse train with ultralow timing jitter enables absolute time-of-flight measurements based on a dual-comb implementation, which is typically composed of a pair of optical frequency combs generated by femtosecond lasers. Dead-zone-free absolute distance measurement with sub-micrometer precision and kHz update rate has been routinely achieved with a dual-comb configuration, which is promising for a number of precision manufacturing applications, from large step-structure measurements prevalent in microelectronic profilometry to three coordinate measurements in large-scale aerospace manufacturing and shipbuilding. In this paper, we first review the sub-femtosecond precision timing jitter characterization methods and approaches for ultralow timing jitter mode-locked fiber laser design. Then, we provide an overview of the state-of-the-art dual-comb absolute ranging technology in terms of working principles, experimental implementations, and measurement precisions. Finally, we discuss the impact of quantum-limited timing jitter on the dual-comb ranging precision at a high update rate. The route to highprecision dual-comb range finder design based on ultralow jitter femtosecond fiber lasers is proposed.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11474257 and 61605183
文摘By employing three reflecting volume Bragg gratings, a near-infrared 4-channel spectral-beam-combining system is demonstrated to present 720 W combined power with a combining efficiency of 94.7%. The combined laser beam is near-diffraction-limited with a beam factor M^2-1.54. During this 4-channel beam-combining process, no special active cooling measures are used to evaluate the volume Bragg gratings as combining elements are under the higher power laser operation. Thermal expansion and period distortion are verified in a 2 k W 2-channel beam-combining process, and the heat issue in the transmission case is found to be more remarkable than that in the diffraction e-se. Transmitted and diffracted beams experience wave-front aberrations with different degrees, thus leading to distinct beam deterioration.
文摘INTRODUCTIONEndoscopy has revolutionised our management of many gastrointestinal disorders over the past 30 years .We are increasingly able to diagnose gastrointestinal (GI) tumors at an early stage,and endoscopic therapy has made a difference to the outcome of GI haemorrhage. We still rely on surgery for cure of cancer of cancer but as diagnostic techniques improve the goal of minimally invasive diagnosis and therapy appears ever more attainable diagnosis and therapy appears vevr more attainable . As populations get older ,it is also increasingly desirable .Laser light can be used for both diagnosis and therapy in the gut .This article reviews the value of lasers in these areas .
基金This study was supported by Princeton University Eric and Wendy Schmidt Transformative Technology Fund.This simulation was funded by Comunidad de Madrid Project ADITIMAT-CM(S2018/NMT-4411)Universidad Politecnicade Madrid Research Grant(EST-PDI-19-A1JMBI-26-T4MNY9).The authors also want to thank Luc Deike for valuable discussions.The authors acknowledge the use of Princeton's Imaging and Analysis Center,which is partially supported by the Princeton Center for Complex Materials,a National Science Foundation(NSF)MRSEC program(DMR-1420541),for the SEM image acquisition.
文摘Laser polishing is widely employed to reduce the surface roughness of products with complex geometries.Traditional laser polishing techniques use a single high-power Gaussian beam to melt and smooth a thin layer of surface material.However,the reliance on high power lasers can present practical challenges such as minimizing surface evaporation or reducing overall cost.In this work,we combined two identical low-power laser beams with a spatial offset in between them to construct an elliptical beam.By changing the spatial offset,combined beams with different lengths along the major axis can be created.We observe over 20%improvement in line roughness reduction using this approach compared to a single Gaussian laser beam with the same total power.Additionally,both experiment and simulation results suggest such improvement is because this dual-laser set-up can create a longer molten pool compared to a single laser.
基金Project supported by Jilin Science and Technology Development Plan,China(Grant Nos.20210201030GX and 20190302052GX)。
文摘A 1040 nm tapered laser with tapered distributed Bragg reflector(DBR) grating is designed and fabricated. By designing the grating with tapered layout, the tapered DBR grating exhibits the scattering effect on side backward-traveling waves, thus achieving additional suppression of parasitic oscillation. Under the suppression of parasitic oscillation, the spatial and spectral characteristics of the tapered laser are improved. The experimental results show that a near-Gaussian far-field distribution and a kink-free P–I characteristics are achieved, and a single peak emission with a wavelength of1046.84 nm and a linewidth of 56 pm is obtained.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61875214,61535014,and 61775225)Scientific Innovation Fund of Chinese Academy of Sciences(Grant No.CXJJ-17S010)
文摘We propose a method to directly measure phase-related noise characteristics of single-frequency lasers in the 728–980 nm band based on a 120°phase difference interferometer.Differential phase information of the laser under test is demodulated via the interferometer.Other parameters related to the phase noise characteristics such as linewidth at different observation time, phase/frequency noise, power spectrum density of phase/frequency fluctuation, and Allan deviation are further obtained.Frequency noise as low as 1 Hz^2/Hz can be measured using our system.Then the phase-related noise characteristics of two commercial lasers frequently used in cold atomic clocks are studied systematically by the method.Furthermore, several influencing factors and their relative evolution laws are also revealed, such as the pump current and frequency-locking control parameters.This would help to optimize the laser performance, select laser sources, and evaluate the system performance for cold atomic physics applications.
文摘InG sP/G s SCH SQW lasers have been prepared by LP-MOCVD. The dependence of t hreshold current density on cavity length was explained. Laser diodes are char acterized by the output power of 1 W to 2 W, threshold current density ( J th ) of 330 A/cm 2 to 450 A/cm 2 and external differe ntial quantum efficiency ( η d) of 35% to 75%, and these characteristics ar e in good agreement with the designed requirement.
基金Project supported by the National Natural Science Foundation of China(Grant No.61925507)the National Key R&D Program of China(Grant No.2017YFE0123700)+5 种基金the Strategic Priority Research Program of Chinese Academic Sciences(Grant No.XDB1603)the Shanghai Municipal Science and Technology Major Project(Grant No.2017SHZDZX02)the Shanghai Natural ScienceFoundation(Grant No.20ZR1464600)the Program of Shanghai Academic/Technology Research Leader(Grant No.18XD1404200)the Shanghai Sailing Program(Grant No.21YF1453800)Youth Innovation Promotion Association of Chinese Academic Sciences(Grant No.Y202059).
文摘We present a cascaded nonlinear spectral broadening scheme for Nd-doped lasers,featuring with long pulse duration and high average power.This scheme is based on two multi-pass cells(MPCs)and one multiple-plate supercontinuum generation(MPSG),and the numerical investigation is driven by a home-made Nd-doped fiber laser with 12 ps pulse duration,50 kHz repetition rate and 100 W average power.The MPC-based first two stages allow us to broaden the pulse spectrum to 4 nm and 43 nm respectively,and subsequently,the MPSG-based third stage allows us to reach 235 nm spectral bandwidth.This broadened spectrum can support a Fourier-transfer-limited pulse duration of 9.8 fs,which is shorter than three optical cycles.To the best of our knowledge,it is the first time to demonstrate the possibility of few-cycle pulses generation based on the 10 ps level Nd-doped lasers.Such few-cycle and high average power laser sources should be attractive and prospective,benefiting from the characteristics of structure compact,low-cost and flexibility.
基金Supported by the National Natural Foundation of China under Grant Nos 61204058 and 61021064the Natural Foundation of Guangdong Province under Grant No S2013010011833the Foundation of Shenzhen Innovation Program under Grant No JCYJ20130401095559823
文摘We report on the measurement of junction temperature of the InAs/InP（l00） quantum dot lasers working in the 1.55μm wavelength region. The measurement is based on analyzing the temperature induced mode shift of the Fabry-Perot cavity. Under pulsed operation mode, more than 20℃ junction temperature rise is measured for the quantum-dot （QD） laser when the duty cycle is increased from 1% to 95%. For a reference quantum well laser, the junction temperature rise is obtained as only around 3℃. The large junction temperature rise might be a crucial factor to improve the performance of QD lasers.
文摘We have carried out the hohlraum experiments about radiation temperature scaling on the Shenguang-Ⅱ （SG- Ⅱ） laser facility with eight laser beams of 0.35#m, pulse duration of about 1.0ns and total energy of 2000J. The reradiated x-ray flux through the laser entrance hole was measured using a soft x-ray spectrometer. The measured peak radiation temperature was 170eV for the standard hohlraum and 150 eV for the 1.5-scaled one. We have derived the radiation temperature scaling law, in which the laser hohlraum coupling efficiency is included. With an appropriate coupling efficiency, the coincidences between experimental and scaling hohlraum radiation temperatures are rather good.
文摘We report on a theoretical and experimental study of an all-normal-dispersion （ANDi） Yb-doped mode-locked fiber laser, in which nonlinear polarization rotation （NPR） is used to realize mode-locking without any dispersion compensation. Based on the coupled nonlinear Schr6dinger （CNLS） equation, a model simulating the mode-locked process of an all-normal-dispersion ring fiber laser is developed, which shows that the achievement of stable mode-locking depends on the alignment of the polarization controller （PC） along the fast-polarization axis of the fiber, the birefringence intensity, and the net cavity dispersion. According to the theoretical analysis, stable mode-locked pulses with pulse duration 300 ps and average output power 33.9 mW at repetition rate 36 MHz are obtained.
文摘Continuous-wave chemical oxygen-iodine lasers (COILs) can be operated in a pulsed operation mode to obtain a higher peak power.The key point is to obtain a uniform and stable glow discharge in the mixture of singlet delta oxygen and iodide.We propose using an electrode system with the assistance of surface sliding pre-ionization to solve the problem of the stable glow discharge with a large aperture.The pre-ionization unit is symmetrically fixed on the plane of the cathode surface.A uniform and stable glow discharge is obtained in a mixture of iodide (such as CH3I) and nitrogen at the specific deposition energy of 4.5 J/L,pressure of 1.99-3.32 kPa,aperture size of 11 cm × 10cm.The electrode system is applied in a pulsed COIL.Laser energy up to 4.4J is obtained and the specific energy output is 2 J/L.
文摘Passively Q-switched quasi-continuous-wave （QCW） diode-pumped Nd：YAG laser with Cr^4＋ ：YAG as saturable absorber is numerically investigated by solving the coupled rate equations. The threshold pump rate for passively Q-switched QCW-pumped laser is derived. The effects of the pump rate and pump-pulse duration on the laser operation characteristics are studied theoretically. The pump power range can be estimated according to the number of output pulses. The numerical simulation results are in good agreement with the experimental results.
基金Supported by the Science and Technology Commission Foundation of Shanghai （Nos 05JC14005, 05SG02）, and the National Natural Science Foundation of China under Grant Nos 60538010, 10376009 and 10576009.
文摘We study a femtosecond Ti：sapphire laser pumped optical parametric amplifier （OPA） at 1053nm. The OPA Generates stable signal pulses with duration smaller than l OOfs, wavelength drift smaller than 0.5 nm, and pulseto-pulse fluctuation of about ±4%, by employinG an external seeder. In a terawatt laser pumped large-aperture LiNbOa OPA, pulse energy at signal has been scaled up to 4mJ. This m J-class femtosecond OPA at 1053nm presents a feasible alternative to optical parametric chirped-pulse amplification, and is ready to be applied to petawatt lasers.
