An effect of the high-power electromagnetic pulses onto the droplet of coal-water slurry inside the furnace was investigated.In contrary to the previously investigated laser-induced fuel atomization that occurs at the...An effect of the high-power electromagnetic pulses onto the droplet of coal-water slurry inside the furnace was investigated.In contrary to the previously investigated laser-induced fuel atomization that occurs at the room temperature,the pre-heated(to 400 K)slurry becomes dry enough to prevent the explosion-like steam formation.Thus,fuel does not atomize and the ignition does not accelerate.Furthermore,the absorption of several laser pulses leads to evident sintering of irradiated surface with following increase of the ignition delay time for up to 24%.Variation of the pulse energy in range 48-118 mJ(corresponding intensity up to 2.4 J·cm^-2)leads to certain variation of the increase of ignition delay.The strong pulsed overheating of the coal water slurry which does not initiate the fine atomization of the fuel generally makes its ignition longer.展开更多
High-power continuous-wave ultraviolet lasers are useful for many applications.As ultraviolet laser sources,the wavelength switching capability and compact structure are very important to extend the applicability and ...High-power continuous-wave ultraviolet lasers are useful for many applications.As ultraviolet laser sources,the wavelength switching capability and compact structure are very important to extend the applicability and improve the flexibility in practical applications.In this work,we present two simple and relatively compact schemes by laser diode pumping to obtain a watt-level single-wavelength 348.7-nm laser and discrete wavelength tunable ultraviolet lasers around 349 nm(from 334.7 to 364.5 nm)by intracavity frequency doubling based on Pr^(3+):YLF andβ-BBO crystals.The maximum output power of the single-wavelength 348.7-nm laser is 1.033 W.The output powers of the discrete wavelength tunable lasers are at the level of tens of milliwatts,except for two peaks at 348.7 and 360.3 nm with output powers of approximately 500 mW.In addition,simulations are carried out to explain the experimental results and clarify the tuning mechanisms.展开更多
The next generation of high-power lasers enables repetition of experiments at orders of magnitude higher frequency than what was possible using the prior generation.Facilities requiring human intervention between lase...The next generation of high-power lasers enables repetition of experiments at orders of magnitude higher frequency than what was possible using the prior generation.Facilities requiring human intervention between laser repetitions need to adapt in order to keep pace with the new laser technology.A distributed networked control system can enable laboratory-wide automation and feedback control loops.These higher-repetition-rate experiments will create enormous quantities of data.A consistent approach to managing data can increase data accessibility,reduce repetitive data-software development and mitigate poorly organized metadata.An opportunity arises to share knowledge of improvements to control and data infrastructure currently being undertaken.We compare platforms and approaches to state-of-the-art control systems and data management at high-power laser facilities,and we illustrate these topics with case studies from our community.展开更多
An all-fiber high-power linearly polarized chirped pulse amplification(CPA)system is experimentally demonstrated.Through stretching the pulse duration to a full width of approximately 2 ns with two cascaded chirped fi...An all-fiber high-power linearly polarized chirped pulse amplification(CPA)system is experimentally demonstrated.Through stretching the pulse duration to a full width of approximately 2 ns with two cascaded chirped fiber Bragg gratings(CFBGs),a maximum average output power of 612 W is achieved from a high-gain Yb-doped fiber that has a core diameter of 20μm with a slope efficiency of approximately 68%at the repetition rate of 80 MHz.At the maximum output power,the polarization degree is 92.5%and the M^(2)factor of the output beam quality is approximately 1.29;the slight performance degradations are attributed to the thermal effects in the main amplifier.By optimizing the B-integral of the amplifier and finely adjusting the higher-order dispersion of one of the CFBGs,the pulse width is compressed to 863 fs at the highest power with a compression efficiency of 72%,corresponding to a maximum compressed average power of 440.6 W,single pulse energy of 5.5μJ and peak power of about 4.67 MW.To the best of our knowledge,this is the highest average power of a femtosecond laser directly generated from an all-fiber linearly polarized CPA system.展开更多
Here we developed a novel wavelength-switchable visible continuous-wave(CW)Pr^(3+):YLF laser around 670 nm.In single-wavelength laser operations,the maximum output powers of 2.60 W,1.26 W,and 0.21 W,the maximum slope ...Here we developed a novel wavelength-switchable visible continuous-wave(CW)Pr^(3+):YLF laser around 670 nm.In single-wavelength laser operations,the maximum output powers of 2.60 W,1.26 W,and 0.21 W,the maximum slope efficiencies of 34.7%,27.3%,and 12.3%were achieved with good beam qualities(M^(2)<1.6)at 670.4 nm,674.2 nm,and 678.9 nm,respectively.Record-high output power(2.6 W)and record-high slope efficiency(34.7%)were achieved for the Pr^(3+):YLF laser operation at 670.4 nm.This is also the first demonstration of longer-wavelength peaks beyond 670 nm in the^(3)P_(1)→^(3)F_(3)transition of Pr^(3+):YLF.In multi-wavelength laser operations,the dual-wavelength lasings,including 670.1/674.8 nm,670.1/679.1 nm,and 675.0/679.4 nm,were obtained by fine adjustment of one/two etalons within the cavity.Furthermore,the triple-wavelength lasings,e.g.672.2/674.2/678.6 nm and 670.4/674.8/679.4 nm,were successfully demonstrated.Moreover,both the first-order vortex lasers(LG_(0)^(+1)and LG_(0)^(-1)modes)at 670.4 nm were obtained by off-axis pumping.展开更多
The first demonstration of laser action in ruby was made in 1960 by T.H.Maiman of Hughes Research Laboratories,USA.Many laboratories worldwide began the search for lasers using different materials,operating at differe...The first demonstration of laser action in ruby was made in 1960 by T.H.Maiman of Hughes Research Laboratories,USA.Many laboratories worldwide began the search for lasers using different materials,operating at different wavelengths.In the UK,academia,industry and the central laboratories took up the challenge from the earliest days to develop these systems for a broad range of applications.This historical review looks at the contribution the UK has made to the advancement of the technology,the development of systems and components and their exploitation over the last 60 years.展开更多
Porous materials have many applications for laser–matter interaction experiments related to inertial confinement fusion.Obtaining new knowledge about the properties of the laser-produced plasma of porous media is a c...Porous materials have many applications for laser–matter interaction experiments related to inertial confinement fusion.Obtaining new knowledge about the properties of the laser-produced plasma of porous media is a challenging task.In this work,we report,for the first time to the best of our knowledge,the time-dependent measurement of the reflected light of a terawatt laser pulse from the laser-produced plasma of low-Z foam material of overcritical density.The experiments have been performed with the ABC laser,with targets constituted by foam of overcritical density and by solid media of the same chemical composition.We implemented in the MULTI-FM code a model for the light reflection to reproduce and interpret the experimental results.Using the simulations together with the experimental results,we indicate a criterion for estimating the homogenization time of the laser-produced plasma,whose measurement is challenging with direct diagnostic techniques and still not achieved.展开更多
Controlling the delivery of multi-terawatt and petawatt laser pulses to final focus,both in position and angle,is critical to many laser applications such as optical guiding,laser–plasma acceleration,and laser-produc...Controlling the delivery of multi-terawatt and petawatt laser pulses to final focus,both in position and angle,is critical to many laser applications such as optical guiding,laser–plasma acceleration,and laser-produced secondary radiation.We present an online,non-destructive laser diagnostic,capable of measuring the transverse position and pointing angle at focus.The diagnostic is based on a unique double-surface-coated wedged-mirror design for the final steering optic in the laser line,producing a witness beam highly correlated with the main beam.By propagating low-power kilohertz pulses to focus,we observed spectra of focus position and pointing angle fluctuations dominated by frequencies below 70 Hz.The setup was also used to characterize the excellent position and pointing angle correlation of the 1 Hz high-power laser pulses to this low-power kilohertz pulse train,opening a promising path to fast non-perturbative feedback concepts even on few-hertz-class high-power laser systems.展开更多
The success of high-power fiber lasers is fueled by maturation of active and passive fibers,combined with the availability of high-power fiber-based components.In this contribution,we first overview the enormous poten...The success of high-power fiber lasers is fueled by maturation of active and passive fibers,combined with the availability of high-power fiber-based components.In this contribution,we first overview the enormous potential of rare-earth doped fibers in spectral coverage and recent developments of key fiber-based components employed in high-power laser systems.Subsequently,the emerging functional active and passive fibers in recent years,which exhibit tremendous advantages in balancing or mitigating parasitic nonlinearities hindering high-power transmission,are outlined from the perspectives of geo-metric and material engineering.Finally,novel functional applications of conventional fiber-based components for nonlinear suppression or spatial mode selection,and correspondingly,the high-power progress of function fiber-based components in power handling are introduced,which suggest more flexible controllability on high-power laser operations.展开更多
It was shown experimentally that for a 65-fs 17-J pulse,the effect of filamentation instability,also known as small-scale self-focusing,is much weaker than that predicted by stationary and nonstationary theoretical mo...It was shown experimentally that for a 65-fs 17-J pulse,the effect of filamentation instability,also known as small-scale self-focusing,is much weaker than that predicted by stationary and nonstationary theoretical models for high B-integral values.Although this discrepancy has been left unexplained at the moment,in practice no signs of filamentation may allow a breakthrough in nonlinear pulse post-compression at high laser energy.展开更多
Propagation properties of high-power fiber laser with high-order-mode(HOM) content are studied numerically for the first time to the best of our knowledge. The effect of HOM on the propagation property is evaluated by...Propagation properties of high-power fiber laser with high-order-mode(HOM) content are studied numerically for the first time to the best of our knowledge. The effect of HOM on the propagation property is evaluated by the power in the bucket(PIB) metric. It is shown that PIB is mainly dependent on HOM content rather than the relative phase between the fundamental mode and HOM. The PIB in vacuum is more than 80% when the power fraction of the HOM is controlled to be less than 50% at 5 km. The relative phase has an impact on the peak intensity position and concentration of the far-field intensity distribution. If an adaptive optics system is used to correct the peak intensity deviation, the results indicate that there exists a maximal value of PIB as relative phase increases. Such effect is weakened when propagating in turbulence. Compared to the laser beams without HOM, laser beams with HOM content are less influenced by the turbulence and can reduce average intensity fluctuation. The results may be useful in the design of a high-power fiber laser system.展开更多
Giant electromagnetic pulses(EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot...Giant electromagnetic pulses(EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot electrons inside the target, which produce radiation across a wide band from DC to terahertz frequencies. Improved understanding and control of EMP is vital as we enter a new era of high repetition rate, high intensity lasers(e.g. the Extreme Light Infrastructure).We present recent data from the VULCAN laser facility that demonstrates how EMP can be readily and effectively reduced. Characterization of the EMP was achieved using B-dot and D-dot probes that took measurements for a range of different target and laser parameters. We demonstrate that target stalk geometry, material composition, geodesic path length and foil surface area can all play a significant role in the reduction of EMP. A combination of electromagnetic wave and 3 D particle-in-cell simulations is used to inform our conclusions about the effects of stalk geometry on EMP,providing an opportunity for comparison with existing charge separation models.展开更多
Suppressing nonlinear effects in high-power fiber lasers based on fiber gratings has become a hotspot.At present,research is mainly focused on suppressing stimulated Raman scattering in a high-power fiber laser.Howeve...Suppressing nonlinear effects in high-power fiber lasers based on fiber gratings has become a hotspot.At present,research is mainly focused on suppressing stimulated Raman scattering in a high-power fiber laser.However,the suppression of spectral broadening,caused by self-phase modulation or four-wave mixing,is still a challenging attribute to the close distance between the broadened laser and signal laser.If using a traditional fiber grating with only one stopband to suppress the spectral broadening,the signal power will be stripped simultaneously.Confronting this challenge,we propose a novel method based on phase-shifted long-period fiber grating(PS-LPFG)to suppress spectral broadening in a high-power fiber master oscillator power amplifier(MOPA)laser system in this paper.A PS-LPFG is designed and fabricated on 10/130 passive fiber utilizing a point-by-point scanning technique.The resonant wavelength of the fabricated PS-LPFG is 1080 nm,the full width at half maximum of the passband is 5.48 nm,and stopband extinction exceeds 90%.To evaluate the performance of the PS-LPFG,the grating is inserted into the seed of a kilowattlevel continuous-wave MOPA system.Experiment results show that the 30 dB linewidth of the output spectrum is narrowed by approximately 37.97%,providing an effective and flexible way for optimizing the output linewidth of highpower fiber MOPA laser systems.展开更多
Composite ceramic phosphor(CCP)is a candidate light-conversion material to obtain the high-quality laser lighting source.Phosphors based on the transmissive configuration model could not simultaneously meet the requir...Composite ceramic phosphor(CCP)is a candidate light-conversion material to obtain the high-quality laser lighting source.Phosphors based on the transmissive configuration model could not simultaneously meet the requirements of angular color uniformity and high thermal stability.In this study,a novel composite structure ceramic was designed,including Al_(2)O_(3)-YAG:Ce/YAG layered ceramic with a size of 1 mm×1 mm for lighting,and Al_(2)O_(3) ceramic(φ=16.0 mm)was used as the wrapping material due to its outstanding thermal stability.The prepared ceramics exhibited excellent thermal performance and no yellow ring phenomenon.Through this design,we achieved the match of the intensity distribution of the blue and yellow lights,resulting in a high angular color uniformity of 0.9 with a view angle of±80°.All ceramics showed no luminous saturation phenomenon,even the laser power density was increased up to 47.51 W/mm^(2).A high-brightness white-light source with a luminous flux of 618 lm,a luminous efficiency of 126 lm/W,a CCT of 6615 K,and a CRI of 69.9 was obtained in the transmissive configuration.In particular,the surface temperature of the ceramic was as low as 74.1℃ under a high laser radiation(47.51 W/mm^(2)).These results indicate that Al_(2)O_(3)/Al_(2)O_(3)-YAG:Ce/YAG composite structure ceramic is a promising luminescent material in the high-power laser lighting applications.展开更多
We present our efforts towards power scaling of Er:Lu_(2)O_(3)lasers at 2.85μm.By applying a dual-end diode-pumped resonator scheme,we achieve an output power of 14.1 W at an absorbed pump power of 59.7 W with a slop...We present our efforts towards power scaling of Er:Lu_(2)O_(3)lasers at 2.85μm.By applying a dual-end diode-pumped resonator scheme,we achieve an output power of 14.1 W at an absorbed pump power of 59.7 W with a slope efficiency of 26%.In a single-end pumped resonator scheme,an output power of 10.1 W is reached under 41.9 W of absorbed pump power.To the best of our knowledge,this is the first single crystalline mid-infrared rare-earth-based solid-state laser with an output power exceeding 10 W at room temperature.展开更多
The design and the early commissioning of the ELI-Beamlines laser facility’s 30 J,30 fs,10 Hz HAPLS(High-repetitionrate Advanced Petawatt Laser System)beam transport(BT)system to the P3 target chamber are described i...The design and the early commissioning of the ELI-Beamlines laser facility’s 30 J,30 fs,10 Hz HAPLS(High-repetitionrate Advanced Petawatt Laser System)beam transport(BT)system to the P3 target chamber are described in detail.It is the world’s first and with 54 m length,the longest distance high average power petawatt(PW)BT system ever built.It connects the HAPLS pulse compressor via the injector periscope with the 4.5 m diameter P3 target chamber of the plasma physics group in hall E3.It is the largest target chamber of the facility and was connected first to the BT system.The major engineering challenges are the required high vibration stability mirror support structures,the high pointing stability optomechanics as well as the required levels for chemical and particle cleanliness of the vacuum vessels to preserve the high laser damage threshold of the dielectrically coated high-power mirrors.A first commissioning experiment at low pulse energy shows the full functionality of the BT system to P3 and the novel experimental infrastructure.展开更多
We present a theoretical study of mode evolution in high-power distributed side-coupled cladding-pumped(DSCCP)fiber amplifiers.A semi-analytical model taking the side-pumping schemes,transverse mode competition,and st...We present a theoretical study of mode evolution in high-power distributed side-coupled cladding-pumped(DSCCP)fiber amplifiers.A semi-analytical model taking the side-pumping schemes,transverse mode competition,and stimulated thermal Rayleigh scattering into consideration has been built,which can model the static and dynamic mode evolution in high-power DSCCP fiber amplifiers.The mode evolution behavior has been investigated with variation of the fiber amplifier parameters,such as the pump power distribution,the length of the DSCCP fiber,the averaged coupling coefficient,the number of the pump cores and the arrangement of the pump cores.Interestingly,it revealed that static mode evolution induced by transverse mode competition is different from the dynamic evolution induced by stimulated thermal Rayleigh scattering.This shows that the high-order mode experiences a slightly higher gain in DSCCP fiber amplifiers,but the mode instability thresholds for DSCCP fiber amplifiers are higher than those for their end-coupled counterparts.By increasing the pump core number and reducing the averaged coupling coefficient,the mode instability threshold can be increased,which indicates that DSCCP fibers can provide additional mitigation strategies of dynamic mode instability.展开更多
Rotation angle of the laser scan direction between two adjacent layers is a key controlling parameter during the high-power (≥ 1 kW) laser powder bed fusion (HP-LPBF) process. This study investigates the influen...Rotation angle of the laser scan direction between two adjacent layers is a key controlling parameter during the high-power (≥ 1 kW) laser powder bed fusion (HP-LPBF) process. This study investigates the influences of rotation angles (θ = 0°, 45°, 90°, 105°) on the surface morphology, microstructure, and mechanical properties of Inconel 718 (IN718) alloy produced by HP-LPBF. Results show that adopting low rotation angles (e.g., 0° and 45°) is prone to relatively poor surface finish and lack-of-fusion defects, whereas adopting high rotation angles (e.g., 90° and 105°) induces smaller surface roughness and better relative density. Each case reveals a noticeable edge effect but the maximal heights witness a downward trend with the increase of rotation angle. There are some minor differences in the primary dendrite arm spacing and grain morphology by varying the rotation angles. Moreover, the tensile property is slightly enhanced as the rotation angle increases. The present work suggests that high rotation angles like 90° and 105° would probably be more favorable for the 1 kW HP-LPBF process than rotation angles with relatively low values.展开更多
The post-compression technique based on self-phase modulation of high-energy pulses leads to an increase in achievable peak power and intensity.Typically,the pulses considered in experiments have been less than 100 fs...The post-compression technique based on self-phase modulation of high-energy pulses leads to an increase in achievable peak power and intensity.Typically,the pulses considered in experiments have been less than 100 fs in duration.Here,the method is applied to the ELFIE laser system at the LULI facility,for a pulse of 7 J energy and an initial measured duration of 350 fs.A 5-mm-thick fused silica window and a 2 mm cyclic-olefin polymer were used as optical nonlinear materials.The 9 cm diameter beam was spectrally broadened to a bandwidth corresponding to 124 fs Fourier-limited pulse duration,and then it was partly post-compressed to 200 fs.After measuring the spatial spectra of the beam fluence,a uniform gain factor of 4 increase in the fluctuations over the studied range of frequencies is observed,due to small-scale self-focusing.展开更多
Laser-induced damage(LID)on high-power laser facilities is one of the limiting factors for the increase in power and energy.Inertial confinement fusion(ICF)facilities such as Laser Mégajoule or the National Ignit...Laser-induced damage(LID)on high-power laser facilities is one of the limiting factors for the increase in power and energy.Inertial confinement fusion(ICF)facilities such as Laser Mégajoule or the National Ignition Facility use spectral broadening of the laser pulse that may induce power modulations because of frequency modulation to amplitude modulation conversion.In this paper,we study the impact of low and fast power modulations of laser pulses both experimentally and numerically.The MELBA experimental testbed was used to shape a wide variety of laser pulses and to study their impact on LID.A 1D Lagrangian hydrodynamic code was used to understand the impact of different power profiles on LID.展开更多
基金performed within the framework of the Russian State Assignment“Science”project FSWW-2020-0022Investigations of the ignition techniques of waste-derived fuels were partially supported by the Tomsk Polytechnic University Competitiveness Enhancement Program(project VIU-ISHFVP-197/2019).
文摘An effect of the high-power electromagnetic pulses onto the droplet of coal-water slurry inside the furnace was investigated.In contrary to the previously investigated laser-induced fuel atomization that occurs at the room temperature,the pre-heated(to 400 K)slurry becomes dry enough to prevent the explosion-like steam formation.Thus,fuel does not atomize and the ignition does not accelerate.Furthermore,the absorption of several laser pulses leads to evident sintering of irradiated surface with following increase of the ignition delay time for up to 24%.Variation of the pulse energy in range 48-118 mJ(corresponding intensity up to 2.4 J·cm^-2)leads to certain variation of the increase of ignition delay.The strong pulsed overheating of the coal water slurry which does not initiate the fine atomization of the fuel generally makes its ignition longer.
基金supported by the National Natural Science Foundation of China(NSFC)(No.61975168)
文摘High-power continuous-wave ultraviolet lasers are useful for many applications.As ultraviolet laser sources,the wavelength switching capability and compact structure are very important to extend the applicability and improve the flexibility in practical applications.In this work,we present two simple and relatively compact schemes by laser diode pumping to obtain a watt-level single-wavelength 348.7-nm laser and discrete wavelength tunable ultraviolet lasers around 349 nm(from 334.7 to 364.5 nm)by intracavity frequency doubling based on Pr^(3+):YLF andβ-BBO crystals.The maximum output power of the single-wavelength 348.7-nm laser is 1.033 W.The output powers of the discrete wavelength tunable lasers are at the level of tens of milliwatts,except for two peaks at 348.7 and 360.3 nm with output powers of approximately 500 mW.In addition,simulations are carried out to explain the experimental results and clarify the tuning mechanisms.
基金A.J.acknowledges the support from DOE Grant#DESC0016804.
文摘The next generation of high-power lasers enables repetition of experiments at orders of magnitude higher frequency than what was possible using the prior generation.Facilities requiring human intervention between laser repetitions need to adapt in order to keep pace with the new laser technology.A distributed networked control system can enable laboratory-wide automation and feedback control loops.These higher-repetition-rate experiments will create enormous quantities of data.A consistent approach to managing data can increase data accessibility,reduce repetitive data-software development and mitigate poorly organized metadata.An opportunity arises to share knowledge of improvements to control and data infrastructure currently being undertaken.We compare platforms and approaches to state-of-the-art control systems and data management at high-power laser facilities,and we illustrate these topics with case studies from our community.
基金This work was supported by the National Natural Science Foundation of China(No.62005316)Director Fund of State Key Laboratory of Pulsed Power Laser Technology(No.SKL2020ZR02).
文摘An all-fiber high-power linearly polarized chirped pulse amplification(CPA)system is experimentally demonstrated.Through stretching the pulse duration to a full width of approximately 2 ns with two cascaded chirped fiber Bragg gratings(CFBGs),a maximum average output power of 612 W is achieved from a high-gain Yb-doped fiber that has a core diameter of 20μm with a slope efficiency of approximately 68%at the repetition rate of 80 MHz.At the maximum output power,the polarization degree is 92.5%and the M^(2)factor of the output beam quality is approximately 1.29;the slight performance degradations are attributed to the thermal effects in the main amplifier.By optimizing the B-integral of the amplifier and finely adjusting the higher-order dispersion of one of the CFBGs,the pulse width is compressed to 863 fs at the highest power with a compression efficiency of 72%,corresponding to a maximum compressed average power of 440.6 W,single pulse energy of 5.5μJ and peak power of about 4.67 MW.To the best of our knowledge,this is the highest average power of a femtosecond laser directly generated from an all-fiber linearly polarized CPA system.
基金supported by the National Natural Science Foundation of China(Nos.11674269,61975168).
文摘Here we developed a novel wavelength-switchable visible continuous-wave(CW)Pr^(3+):YLF laser around 670 nm.In single-wavelength laser operations,the maximum output powers of 2.60 W,1.26 W,and 0.21 W,the maximum slope efficiencies of 34.7%,27.3%,and 12.3%were achieved with good beam qualities(M^(2)<1.6)at 670.4 nm,674.2 nm,and 678.9 nm,respectively.Record-high output power(2.6 W)and record-high slope efficiency(34.7%)were achieved for the Pr^(3+):YLF laser operation at 670.4 nm.This is also the first demonstration of longer-wavelength peaks beyond 670 nm in the^(3)P_(1)→^(3)F_(3)transition of Pr^(3+):YLF.In multi-wavelength laser operations,the dual-wavelength lasings,including 670.1/674.8 nm,670.1/679.1 nm,and 675.0/679.4 nm,were obtained by fine adjustment of one/two etalons within the cavity.Furthermore,the triple-wavelength lasings,e.g.672.2/674.2/678.6 nm and 670.4/674.8/679.4 nm,were successfully demonstrated.Moreover,both the first-order vortex lasers(LG_(0)^(+1)and LG_(0)^(-1)modes)at 670.4 nm were obtained by off-axis pumping.
文摘The first demonstration of laser action in ruby was made in 1960 by T.H.Maiman of Hughes Research Laboratories,USA.Many laboratories worldwide began the search for lasers using different materials,operating at different wavelengths.In the UK,academia,industry and the central laboratories took up the challenge from the earliest days to develop these systems for a broad range of applications.This historical review looks at the contribution the UK has made to the advancement of the technology,the development of systems and components and their exploitation over the last 60 years.
基金funded from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement number 633053。
文摘Porous materials have many applications for laser–matter interaction experiments related to inertial confinement fusion.Obtaining new knowledge about the properties of the laser-produced plasma of porous media is a challenging task.In this work,we report,for the first time to the best of our knowledge,the time-dependent measurement of the reflected light of a terawatt laser pulse from the laser-produced plasma of low-Z foam material of overcritical density.The experiments have been performed with the ABC laser,with targets constituted by foam of overcritical density and by solid media of the same chemical composition.We implemented in the MULTI-FM code a model for the light reflection to reproduce and interpret the experimental results.Using the simulations together with the experimental results,we indicate a criterion for estimating the homogenization time of the laser-produced plasma,whose measurement is challenging with direct diagnostic techniques and still not achieved.
基金the U.S.Department of Energy(DOE),Office of Science,the Office of Basic Energy Sciences,and the Office of High Energy Physics,under Contract No.DE-AC02-05CH11231the Gordon and Betty Moore Foundation under Grant No.GBMF4898.
文摘Controlling the delivery of multi-terawatt and petawatt laser pulses to final focus,both in position and angle,is critical to many laser applications such as optical guiding,laser–plasma acceleration,and laser-produced secondary radiation.We present an online,non-destructive laser diagnostic,capable of measuring the transverse position and pointing angle at focus.The diagnostic is based on a unique double-surface-coated wedged-mirror design for the final steering optic in the laser line,producing a witness beam highly correlated with the main beam.By propagating low-power kilohertz pulses to focus,we observed spectra of focus position and pointing angle fluctuations dominated by frequencies below 70 Hz.The setup was also used to characterize the excellent position and pointing angle correlation of the 1 Hz high-power laser pulses to this low-power kilohertz pulse train,opening a promising path to fast non-perturbative feedback concepts even on few-hertz-class high-power laser systems.
基金supported by the National Natural Science Foundation of China(No.62035015,No.61805280,No.62061136013)Innovation Group of Hunan Province,China(No.2019JJ10005)+1 种基金Hunan Innovative Province Construction Project,China(No.2019RS3017)the Research Plan of National University of Defense Technology(No.ZK19-07).
文摘The success of high-power fiber lasers is fueled by maturation of active and passive fibers,combined with the availability of high-power fiber-based components.In this contribution,we first overview the enormous potential of rare-earth doped fibers in spectral coverage and recent developments of key fiber-based components employed in high-power laser systems.Subsequently,the emerging functional active and passive fibers in recent years,which exhibit tremendous advantages in balancing or mitigating parasitic nonlinearities hindering high-power transmission,are outlined from the perspectives of geo-metric and material engineering.Finally,novel functional applications of conventional fiber-based components for nonlinear suppression or spatial mode selection,and correspondingly,the high-power progress of function fiber-based components in power handling are introduced,which suggest more flexible controllability on high-power laser operations.
基金This work was supported by the Ministry of Science and Higher Education of the Russian Federation No.075-15-2020-906(Center of Excellence‘Center of Photonics’).
文摘It was shown experimentally that for a 65-fs 17-J pulse,the effect of filamentation instability,also known as small-scale self-focusing,is much weaker than that predicted by stationary and nonstationary theoretical models for high B-integral values.Although this discrepancy has been left unexplained at the moment,in practice no signs of filamentation may allow a breakthrough in nonlinear pulse post-compression at high laser energy.
基金sponsored by the Innovation Foundation for Excellent Graduates in the National University of Defense Technology under grant no. B120704the Open Research Fund of Key Laboratory of Atmospheric Composition and Optical Radiation under grant no.2012JJ05
文摘Propagation properties of high-power fiber laser with high-order-mode(HOM) content are studied numerically for the first time to the best of our knowledge. The effect of HOM on the propagation property is evaluated by the power in the bucket(PIB) metric. It is shown that PIB is mainly dependent on HOM content rather than the relative phase between the fundamental mode and HOM. The PIB in vacuum is more than 80% when the power fraction of the HOM is controlled to be less than 50% at 5 km. The relative phase has an impact on the peak intensity position and concentration of the far-field intensity distribution. If an adaptive optics system is used to correct the peak intensity deviation, the results indicate that there exists a maximal value of PIB as relative phase increases. Such effect is weakened when propagating in turbulence. Compared to the laser beams without HOM, laser beams with HOM content are less influenced by the turbulence and can reduce average intensity fluctuation. The results may be useful in the design of a high-power fiber laser system.
基金funding from EPSRC grants EP/L01663X/1 and EP/L000644/1the Newton UK grant+1 种基金the National Natural Science Foundation of China NSFC/11520101003the LLNL Academic Partnership in ICF
文摘Giant electromagnetic pulses(EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot electrons inside the target, which produce radiation across a wide band from DC to terahertz frequencies. Improved understanding and control of EMP is vital as we enter a new era of high repetition rate, high intensity lasers(e.g. the Extreme Light Infrastructure).We present recent data from the VULCAN laser facility that demonstrates how EMP can be readily and effectively reduced. Characterization of the EMP was achieved using B-dot and D-dot probes that took measurements for a range of different target and laser parameters. We demonstrate that target stalk geometry, material composition, geodesic path length and foil surface area can all play a significant role in the reduction of EMP. A combination of electromagnetic wave and 3 D particle-in-cell simulations is used to inform our conclusions about the effects of stalk geometry on EMP,providing an opportunity for comparison with existing charge separation models.
基金supported by the National Key Research and Development Program of China(No.2017YFB1104402)the Pre-research Foundation of Equipment Development Department(No.61404140105)+3 种基金the Key Laboratory of Optical System Advanced Manufacturing Technology of the Chinese Academy of Sciences(No.KLOMT190101)the Jiangsu Provincial Key Research and Development Program(No.BE2019114)the Basic Research Program of Jiangsu Province(No.BK20190456)the National Natural Science Foundation of China(No.62005120)。
文摘Suppressing nonlinear effects in high-power fiber lasers based on fiber gratings has become a hotspot.At present,research is mainly focused on suppressing stimulated Raman scattering in a high-power fiber laser.However,the suppression of spectral broadening,caused by self-phase modulation or four-wave mixing,is still a challenging attribute to the close distance between the broadened laser and signal laser.If using a traditional fiber grating with only one stopband to suppress the spectral broadening,the signal power will be stripped simultaneously.Confronting this challenge,we propose a novel method based on phase-shifted long-period fiber grating(PS-LPFG)to suppress spectral broadening in a high-power fiber master oscillator power amplifier(MOPA)laser system in this paper.A PS-LPFG is designed and fabricated on 10/130 passive fiber utilizing a point-by-point scanning technique.The resonant wavelength of the fabricated PS-LPFG is 1080 nm,the full width at half maximum of the passband is 5.48 nm,and stopband extinction exceeds 90%.To evaluate the performance of the PS-LPFG,the grating is inserted into the seed of a kilowattlevel continuous-wave MOPA system.Experiment results show that the 30 dB linewidth of the output spectrum is narrowed by approximately 37.97%,providing an effective and flexible way for optimizing the output linewidth of highpower fiber MOPA laser systems.
基金the National Key R&D Program of China(2021YFB3501700,2023YFB3506600)National Natural Science Foundation of China(52202135,61975070,and 52302141)+5 种基金Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD),International S&T Cooperation Program of Jiangsu Province(BZ2023007)Key Research and Development Project of Jiangsu Province(BE2023050,BE2021040)Natural Science foundation of Jiangsu Province(BK20221226)Graduate Research and Innovation Projects of Jiangsu Province(KYCX22_2845)Special Project for Technology Innovation of Xuzhou City(KC23380,KC21379,KC22461,and KC22497)Open Project of State Key Laboratory of Crystal Materials(KF2205).
文摘Composite ceramic phosphor(CCP)is a candidate light-conversion material to obtain the high-quality laser lighting source.Phosphors based on the transmissive configuration model could not simultaneously meet the requirements of angular color uniformity and high thermal stability.In this study,a novel composite structure ceramic was designed,including Al_(2)O_(3)-YAG:Ce/YAG layered ceramic with a size of 1 mm×1 mm for lighting,and Al_(2)O_(3) ceramic(φ=16.0 mm)was used as the wrapping material due to its outstanding thermal stability.The prepared ceramics exhibited excellent thermal performance and no yellow ring phenomenon.Through this design,we achieved the match of the intensity distribution of the blue and yellow lights,resulting in a high angular color uniformity of 0.9 with a view angle of±80°.All ceramics showed no luminous saturation phenomenon,even the laser power density was increased up to 47.51 W/mm^(2).A high-brightness white-light source with a luminous flux of 618 lm,a luminous efficiency of 126 lm/W,a CCT of 6615 K,and a CRI of 69.9 was obtained in the transmissive configuration.In particular,the surface temperature of the ceramic was as low as 74.1℃ under a high laser radiation(47.51 W/mm^(2)).These results indicate that Al_(2)O_(3)/Al_(2)O_(3)-YAG:Ce/YAG composite structure ceramic is a promising luminescent material in the high-power laser lighting applications.
基金supported by the National Natural Science Foundation of China(Nos.62175132,61605100,and 12174212)the Natural Science Foundation of Shandong Province(Nos.ZR2020MF116 and ZR2019MF061)the Young Scholars Program of Shandong University。
文摘We present our efforts towards power scaling of Er:Lu_(2)O_(3)lasers at 2.85μm.By applying a dual-end diode-pumped resonator scheme,we achieve an output power of 14.1 W at an absorbed pump power of 59.7 W with a slope efficiency of 26%.In a single-end pumped resonator scheme,an output power of 10.1 W is reached under 41.9 W of absorbed pump power.To the best of our knowledge,this is the first single crystalline mid-infrared rare-earth-based solid-state laser with an output power exceeding 10 W at room temperature.
基金The authors acknowledge support from the project Advanced Research Using High-Intensity Laser-Produced Photons and Particles(ADONIS)(CZ.02.1.01/0.0/0.0/16—019/0000789)by the project High Field Initiative(HiFI)(CZ.02.1.01/0.0/0.0/15_003/0000449),both from European Regional Development Fund.
文摘The design and the early commissioning of the ELI-Beamlines laser facility’s 30 J,30 fs,10 Hz HAPLS(High-repetitionrate Advanced Petawatt Laser System)beam transport(BT)system to the P3 target chamber are described in detail.It is the world’s first and with 54 m length,the longest distance high average power petawatt(PW)BT system ever built.It connects the HAPLS pulse compressor via the injector periscope with the 4.5 m diameter P3 target chamber of the plasma physics group in hall E3.It is the largest target chamber of the facility and was connected first to the BT system.The major engineering challenges are the required high vibration stability mirror support structures,the high pointing stability optomechanics as well as the required levels for chemical and particle cleanliness of the vacuum vessels to preserve the high laser damage threshold of the dielectrically coated high-power mirrors.A first commissioning experiment at low pulse energy shows the full functionality of the BT system to P3 and the novel experimental infrastructure.
基金funded by the National Natural Science Foundation of China(NSFC)(61905226)the Youth Talent Climbing Foundation of the Research Center of Laser Fusion。
文摘We present a theoretical study of mode evolution in high-power distributed side-coupled cladding-pumped(DSCCP)fiber amplifiers.A semi-analytical model taking the side-pumping schemes,transverse mode competition,and stimulated thermal Rayleigh scattering into consideration has been built,which can model the static and dynamic mode evolution in high-power DSCCP fiber amplifiers.The mode evolution behavior has been investigated with variation of the fiber amplifier parameters,such as the pump power distribution,the length of the DSCCP fiber,the averaged coupling coefficient,the number of the pump cores and the arrangement of the pump cores.Interestingly,it revealed that static mode evolution induced by transverse mode competition is different from the dynamic evolution induced by stimulated thermal Rayleigh scattering.This shows that the high-order mode experiences a slightly higher gain in DSCCP fiber amplifiers,but the mode instability thresholds for DSCCP fiber amplifiers are higher than those for their end-coupled counterparts.By increasing the pump core number and reducing the averaged coupling coefficient,the mode instability threshold can be increased,which indicates that DSCCP fibers can provide additional mitigation strategies of dynamic mode instability.
文摘Rotation angle of the laser scan direction between two adjacent layers is a key controlling parameter during the high-power (≥ 1 kW) laser powder bed fusion (HP-LPBF) process. This study investigates the influences of rotation angles (θ = 0°, 45°, 90°, 105°) on the surface morphology, microstructure, and mechanical properties of Inconel 718 (IN718) alloy produced by HP-LPBF. Results show that adopting low rotation angles (e.g., 0° and 45°) is prone to relatively poor surface finish and lack-of-fusion defects, whereas adopting high rotation angles (e.g., 90° and 105°) induces smaller surface roughness and better relative density. Each case reveals a noticeable edge effect but the maximal heights witness a downward trend with the increase of rotation angle. There are some minor differences in the primary dendrite arm spacing and grain morphology by varying the rotation angles. Moreover, the tensile property is slightly enhanced as the rotation angle increases. The present work suggests that high rotation angles like 90° and 105° would probably be more favorable for the 1 kW HP-LPBF process than rotation angles with relatively low values.
基金This work was supported by the Center of Excellence‘Center of Photonics’,Ministry of Science and Higher Education of the Russian Federation(contract No.075-15-2020-906)Project ELI-RO 16/2020 SBUF funded by the Institute for Atomic Physics(IFA)and by the Council for Doctoral Studies(CSUD),University of Bucharest.
文摘The post-compression technique based on self-phase modulation of high-energy pulses leads to an increase in achievable peak power and intensity.Typically,the pulses considered in experiments have been less than 100 fs in duration.Here,the method is applied to the ELFIE laser system at the LULI facility,for a pulse of 7 J energy and an initial measured duration of 350 fs.A 5-mm-thick fused silica window and a 2 mm cyclic-olefin polymer were used as optical nonlinear materials.The 9 cm diameter beam was spectrally broadened to a bandwidth corresponding to 124 fs Fourier-limited pulse duration,and then it was partly post-compressed to 200 fs.After measuring the spatial spectra of the beam fluence,a uniform gain factor of 4 increase in the fluctuations over the studied range of frequencies is observed,due to small-scale self-focusing.
文摘Laser-induced damage(LID)on high-power laser facilities is one of the limiting factors for the increase in power and energy.Inertial confinement fusion(ICF)facilities such as Laser Mégajoule or the National Ignition Facility use spectral broadening of the laser pulse that may induce power modulations because of frequency modulation to amplitude modulation conversion.In this paper,we study the impact of low and fast power modulations of laser pulses both experimentally and numerically.The MELBA experimental testbed was used to shape a wide variety of laser pulses and to study their impact on LID.A 1D Lagrangian hydrodynamic code was used to understand the impact of different power profiles on LID.
