Combined pulsed laser(CPL),introduced in 1975 for target damage,integrates different lasers to achieve high peak power and pulse energy.However,despite decades of research,CPL remains unused for long-range target dama...Combined pulsed laser(CPL),introduced in 1975 for target damage,integrates different lasers to achieve high peak power and pulse energy.However,despite decades of research,CPL remains unused for long-range target damage due to the challenge of maintaining high peak power density over long distances.We note that a potential solution lies in leveraging the air filament generated by femtosecond laser,which can transmit peak power densities higher than 1014 W/cm^(2)under the power clamping effect.To address this,a concept of a femtosecond laser induced air filament-CW CPL for surface damage of ceramics was introduced.We found no surface changes in ceramic targets when irradiated with a CW laser alone.By way of contrast,the target can be penetrated in a very short time(20 ms)with the assistance of the femtosecond laser induced air filament.In this context,we employ high-speed shadow imaging,cross-timescale simulation models and macro-microscopic characterization,to elucidate the CPL damage mechanism.The optimal CPL,combining a 1 mJ femtosecond laser and a 500 W CW laser,yields a damage rate of 1.51×10^(7)μm^(3)/J,representing an improvement of approximately 175%compared to single femtosecond laser ablation and around 59%enhancement compared to coating-assisted CW laser ablation.Furthermore,the efficacy of the proposed femtosecond-CW CPL method is demonstrated in causing penetration damage of ceramic/metal composite material or direct damage of sapphire,showcasing its versatility in damaging applications.Consequently,the femtosecond-CW CPL ablation method presented in this paper holds great promise as a new type of damage method for transparent hard and brittle materials.展开更多
We demonstrate few-cycle pulse generation based on double-stage all-fiber nonlinear pulse compression from a thulium-doped fiber laser at a repetition rate of∼199.74 MHz.The homemade laser provides an average power o...We demonstrate few-cycle pulse generation based on double-stage all-fiber nonlinear pulse compression from a thulium-doped fiber laser at a repetition rate of∼199.74 MHz.The homemade laser provides an average power of 130 mW,serving as the seed for subsequent amplification.After amplification,significant spectral broadening to an octave-spanning bandwidth(1.2 to 2.4μm)is attained through self-phase modulation-dominated nonlinear effects in an ultrahigh numerical aperture fiber and a highly nonlinear fiber.Followed by a two-stage nonlinear compressor,the system directly delivers near transform-limited pulses with a pulse duration of 19.8 fs(2.9 cycles at a central wavelength of 2000 nm)and a pulse energy of 3.37 nJ.To the best of our knowledge,this result is the shortest pulse duration directly generated from a thulium-doped fiber laser.This robust and simplified all-fiber system provides a promising route toward practical mid-infrared frequency comb generation and mid-infrared spectroscopy.展开更多
High-energy continuous wave(CW)lasers are mostly used in laser damage applications,but efficient laser ablation of transparent materials is challenging due to low optical absorption.Considering the potential of femtos...High-energy continuous wave(CW)lasers are mostly used in laser damage applications,but efficient laser ablation of transparent materials is challenging due to low optical absorption.Considering the potential of femtosecond(fs)laser-induced air filament for high-peak laser transmission over long distances,femtosecond(fs)laser-induced air filaments are combined with a millisecond(ms)laser to form an fs-ms CPL,enhancing the efficiency of sapphire ablation through synchronized spatial-temporal focusing.Experimental results show that ablation efficiency increases with the ms peak power and duty ratio.Excessive thermal stress leads to fragmentation of the sapphire when the ms duty ratio is over 30%at the peak power of 800 W,or when the peak power is over 500 W at a duty ratio of 100%.Also,the mechanism of high-efficiency damage is revealed through in-situ high-speed imaging.According to it,the ablation process went through 4 stages within 1.5 ms:defect-creating,melting and ablation,spattering,and fragmentation.Finally,the equivalent ablation efficiency of the fs-ms CPL is as high as 1.73×10^(7)μm^(3)/J,about 28 times higher compared to the fs laser only.The CPL damage method explored in this paper can provide theoretical guidance for efficient laser damage of transparent materials.展开更多
We demonstrate the growth,thermal,spectroscopy and laser performance of an Er3+doped Gdo.iYo.9AlO3(Er:GYAP)disorder crystal grown by Czochralski method.The crystal with space group Pbnm and lattice parameters of a=0.5...We demonstrate the growth,thermal,spectroscopy and laser performance of an Er3+doped Gdo.iYo.9AlO3(Er:GYAP)disorder crystal grown by Czochralski method.The crystal with space group Pbnm and lattice parameters of a=0.5185 nm,b=0.5327 nm,c=0.7378 nm,α=β=90°and V=0.203784 nm3 are obtained by fitting powder X-ray diffraction data.The Mohr's hardnesses along three axes are 6.94,7.27,and 7.44.The thermal expansion coefficient of b axis is 4.20×10^(-6)k^(-1)and the density is 5.88 g/cm3.The thermal conductivities are characterized as K_(a)=6.24,K_(b)=5.57,and K_(c)=6.83 W/(m·K).Meanwhile,the refractive index,absorption and emission spectra in triaxial di-rections are determined.Besides,level lifetimes of 4l11/2 and 413/2 are 0.86 and 2.83 ms.Finally,the~2.7μm multiwavelength laser outputs are observed with maximum average power of 628 mW and beam quality factors M_(x)^(2)/M_(y)^(2) of 1.42/1.45.The results prove that the Er:GYAP crystal is a promising gain medium for generating mid-infrared lasers.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
In this paper,we investigate laser cleaning using a flattened top laser to remove paint coating from a metal substrate.Under the irradiation of a flattened top laser,the coating paint of the metal substrate can be rem...In this paper,we investigate laser cleaning using a flattened top laser to remove paint coating from a metal substrate.Under the irradiation of a flattened top laser,the coating paint of the metal substrate can be removed efficiently by laser induced ablation,stress,and displacement force.The temperature distribution,stress,and displacement are calculated in the coating layer and substrate using finite element analysis.The effects of a Gaussian laser and a flattened top laser and the results of different diameters of laser spot are compared.The investigation shows that the flattened top laser can reduce the substrate damage and enhance the cleaning efficiency.This method meets the need of large area industrial cleaning applications by optimizing the flattened top laser parameters.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
Purpose:To evaluate the clinical efficacy of Pattern Scan Laser Photocoagulator (PASCAL) by observing the efficacy of PASCAL on retinopathy.Methods:A total of 92 patients with retinopathy (121 eyes) who underwent PASC...Purpose:To evaluate the clinical efficacy of Pattern Scan Laser Photocoagulator (PASCAL) by observing the efficacy of PASCAL on retinopathy.Methods:A total of 92 patients with retinopathy (121 eyes) who underwent PASCAL between December 2008 and February 2009 in our center were retrospectively analyzed to evaluate the visual acuity changes and recovery conditions of the patients from baseline to posterior to the treatment.The retinopathy included:diabetic retinopathy,ischemic retinal vein occlusion.(IRVO),central serous chorioretinopathy (CSC),retinal periphlebitis (Eales disease) and retinal degeneration /holes.Results:The patients were subject to a 12-month follow up after PASCAL.The visual acuity findings were stated as below:for diabetic retinopathy.(73 eyes),10 eyes had improved visual acuity;55 eyes were stabilized and 8 eyes progressed;for IRVO (13 eyes),4 eyes showed improvement,6 eyes were stabilized and 3 eyes progressed;for CSC (9 eyes),6 eyes were alleviated and 3 eyes progressed;for retinal periphlebitis (5 eyes),2 eyes had enhanced visual acuity and 3 eyes showed stable visual acuity;for retinal degeneration /holes (21 eyes),5 eyes presented improved visu-al acuity,16 eyes were stabilized and no eye progressed.Indirect ophthalmoscopic reexamination confirmed secured blockage by laser spots and favorable absorption of the retinal edema and newborn capillaries.No obvious leakage was observed during fundus fluorescein angiography and no laser-related ocular adverse effect was reported.Conclusion:PASCAL is accurate,effective and well-tolerated.The duration of short laser pulse falls within the safety range,ensuring the stabilization and improvement in the pa-tient's visual acuity.The parameters,long-term efficacy and complications of PASCAL should be further demonstrated by performing long-term clinical trials with larger sample size.展开更多
A Kerr-lens mode-locked Ti：sapphire laser operating in a non-soliton regime is demonstrated. Dispersive wave generation is observed as a result of third order dispersion in the vicinity of zero dispersion. The charac...A Kerr-lens mode-locked Ti：sapphire laser operating in a non-soliton regime is demonstrated. Dispersive wave generation is observed as a result of third order dispersion in the vicinity of zero dispersion. The characteristics of the Ti：sapphire l^ser operating in a positive dispersion regime are presented, where the oscillator directly generates pulses with duration continuously tunable from 0.37 ps to 2.11 ps, and 36 fs pulses are achieved atter extracavity compression. The oscillation is numerically simulated with an extended nonlinear Schr6dinger equation, and the simulation results are in good agreement with the experimental results.展开更多
In this paper, results are presented on first application of laser-induced breakdown spectroscopy （LIBS） technique for quantitative determination of Mg concentration in alpha-olefins. It is demonstrated that this te...In this paper, results are presented on first application of laser-induced breakdown spectroscopy （LIBS） technique for quantitative determination of Mg concentration in alpha-olefins. It is demonstrated that this technique gives accuracies in Mg concentrations which are comparable with those of traditional methods, as ICP-OES, in short times and without need for sample preparation. Limits of detection for Mg of the order of 500 ppb are demonstrated. Moreover, a brief discussion about the realization of orooer calibration curves and the definition of the limit of detection （LOD） is reoorted.展开更多
Based on the normal pulsed laser ablation method,femtosecond pulsed laser deposition(fs-PLD)is adopted in vacuum for the production of TiO2nanoparticle-assembled films.We study the morphology and electronic characteri...Based on the normal pulsed laser ablation method,femtosecond pulsed laser deposition(fs-PLD)is adopted in vacuum for the production of TiO2nanoparticle-assembled films.We study the morphology and electronic characteristics of TiO2nanoparticle-assembled films deposited at different oxygen background gas pressures from high vacuum(~10-4Pa)to 100 Pa and different deposition time.Our results show that TiO2nanoparticle-assembled films obtained in high vacuum present both a mixture with rutile phase and anatase phase and a pure rutile phase.At the same time,there are more mesoporous structures in the film after annealing,which is beneficial for the enhancement of photocatalytic activity.In water splitting experiment,part of the TiO2nanoparticle-assembled films embedded with a small mass fraction of CdS nanoparticles(~5%)present an interesting photocurrent enhancement with a maximum value of^0.2mA/cm2under a solar simulator.展开更多
Forward fast protons are generated by the moderate-intensity laser-foil interaction. Protons with maximum energy 190 keV are measured by using magnetic spectrometer and CR-39 solid state track detectors along the dire...Forward fast protons are generated by the moderate-intensity laser-foil interaction. Protons with maximum energy 190 keV are measured by using magnetic spectrometer and CR-39 solid state track detectors along the direction normal to the rear surface. The experimental results are also modeled by the paxticle-in-cell method, investigating the timevarying electron temperature and the rear sheath field. The temporal and spatial structure of the sheath electrical field, revealed in the simulation, suggests that these protons are accelerated by target normal sheath acceleration （TNSA） mechanism.展开更多
Since the first laser was invented,the pursuit of high-energy lasers(HELs)has always been enthusiastic.The first revolution of HELs was pushed by the fusion of laser and aerospace in the 1960s,with the chemical rocket...Since the first laser was invented,the pursuit of high-energy lasers(HELs)has always been enthusiastic.The first revolution of HELs was pushed by the fusion of laser and aerospace in the 1960s,with the chemical rocket engines giving fresh impetus to the birth of gas flow and chemical lasers,which finally turned megawatt lasers from dream into reality.Nowadays,the development of HELs has entered the age of electricity as well as the rocket engines.The properties of current electric rocket engines are highly consistent with HELs’goals,including electrical driving,effective heat dissipation,little medium consumption and extremely light weight and size,which inspired a second fusion of laser and aerospace and motivated the exploration for potential HELs.As an exploratory attempt,a new configuration of diode pumped metastable rare gas laser was demonstrated,with the gain generator resembling an electric rocket-engine for improved power scaling ability.展开更多
This article summarizes work at the Laser Thermal Laboratory and discusses related studies on the laser synthesis and functionalization of semiconductor nanostructures and two-dimensional(2D)semiconductor materials.Re...This article summarizes work at the Laser Thermal Laboratory and discusses related studies on the laser synthesis and functionalization of semiconductor nanostructures and two-dimensional(2D)semiconductor materials.Research has been carried out on the laser-induced crystallization of thin films and nanostructures.The in situ transmission electron microscopy(TEM)monitoring of the crystallization of amorphous precursors in nanodomains is discussed herein.The directed assembly of silicon nanoparticles and the modulation of their optical properties by phase switching is presented.The vapor-liquid-solid mechanism has been adopted as a bottom-up approach in the synthesis of semiconducting nanowires(NWs).In contrast to furnace heating methods,laser irradiation offers high spatial selectivity and precise control of the heating mechanism in the time domain.These attributes enabled the investigation of NW nucleation and the early stage of nanostructure growth.Site-and shape-selective,on-demand direct integration of oriented NWs was accomplished.Growth of discrete silicon NWs with nanoscale location selectivity by employing near-field laser illumination is also reported herein.Tuning the properties of 2D transition metal dichalcogenides(TMDCs)by modulating the free carrier type,density,and composition can offer an exciting new pathway to various practical nanoscale electronics.In situ Raman probing of laser-induced processing of TMDC flakes was conducted in a TEM instrument.展开更多
We report on the biodegradation of pure hydrocarbons and chemotaxis towards these compounds by an isolated chlorophenol degrader,Pseudomonas strain H.The biochemical and phylogenetic analysis of the 16S rDNA sequence ...We report on the biodegradation of pure hydrocarbons and chemotaxis towards these compounds by an isolated chlorophenol degrader,Pseudomonas strain H.The biochemical and phylogenetic analysis of the 16S rDNA sequence identified Pseudomonas strain H as having 99.56% similarity with P.aeruginosa PA01.This strain was able to degrade n-hexadecane,1-undecene,1-nonene,1-decene,1-dodecene and kerosene.It grew in the presence of 1-octene,while this hydrocarbons is toxic to other hydrocarbons degraders.Pseudomonas strain H was also chemotactic towards n-hexadecane,kerosene,1-undecene and 1-dodecene.These results show that this Pseudomonas strain H is an attractive candidate for hydrocarbon-containing wastewater bioremediation in controlled environments.Since the classical standard techniques for detecting chemotaxis are not efficient at low bacterial concentrations,we demonstrate the use of the dynamic speckle laser method,which is simple and inexpensive,to confirm bacterial chemotaxis at low cell concentrations （less than 105 colony-forming unit per millilitre （CFU/mL）） when hydrocarbons are the attractants.展开更多
The morphologies of the deposited dots on the 40 nm-thick copper film by the femtosecond laser-induced forward transfer that depend on the irradiated laser fluence have been studied, and the variations of orderliness ...The morphologies of the deposited dots on the 40 nm-thick copper film by the femtosecond laser-induced forward transfer that depend on the irradiated laser fluence have been studied, and the variations of orderliness of the diameter of deposited dots on the quartz substrate and forward ablated dot on the donor substrate with increasing pulse fluence have been obtained experimentally. The experimental results show that a thinner copper film would generate larger-sized ablated dot and deposited dot at the threshold fluence for transfer. By x-ray diffraction measurement, it is demonstrated that the crystal form of the transferred copper films is unaltered and the size of the crystallites is diminished.展开更多
We investigate the kinetic energy of expanding plasma of a solid target heated by a ultra-short and ultra-intense laser pulse and the efllciency of energy coupling between the ultra-intense laser pulse and the solid t...We investigate the kinetic energy of expanding plasma of a solid target heated by a ultra-short and ultra-intense laser pulse and the efllciency of energy coupling between the ultra-intense laser pulse and the solid target, in order to increase the utilization ratio of laser energy and to raise the neutron generation farther. Some new ideas about improving the energy utilization by head-on collision~, between the expanding plasmas are proposed. The significance is the raise of generation of shorter duration neutron, of the order of picoseconds, which allows for an increase of energy resolution in time-of-flight experiments and also for the investigation of the dynamics of nuclear processes with high temporal resolution.展开更多
Usually,only focused femtosecond(fs)lasers at near-infrared(NIR)range can induce photo-damage to transparent cells,making it difficult to treat large amount of cells by such optical methods for photostimulation.In thi...Usually,only focused femtosecond(fs)lasers at near-infrared(NIR)range can induce photo-damage to transparent cells,making it difficult to treat large amount of cells by such optical methods for photostimulation.In this study,we clarify the mechanism of photodamage to cells that are co-cultured with gold nanorods(GNRs)by fs laser.The pulse duration and repetition rate of the fs laser play a key role in cell damage suggesting that the heat accumulation con-tributes to the major part for the cell damage rather than the high peak power which mainly determines the efficiency of multiphoton excitation.We further show that cellular Ca^(2+)can also be released in this scheme,but the process is more sensitive to peak power.Our results can provide a large-scale GNR-mediated photostimulation for cell signaling modulation.展开更多
We used transition radiation techniques instead of the original phosphor targets to improve the electronic beam diagnostic system at Beijing Free Electron Laser.The beam profile,size(3.3×2.4mm),position and diver...We used transition radiation techniques instead of the original phosphor targets to improve the electronic beam diagnostic system at Beijing Free Electron Laser.The beam profile,size(3.3×2.4mm),position and divergence angle(σrms=2.5mrad)in transverse have been obtained from optical transition radiation.We also present the experimental set-up and some preliminary results.展开更多
A femtosecond Kerr-lens mode-locked Cr:LiSGaF laser based on a compact cavity geometry is demonstrated.With a combination of 488,476,and 458nm lines as a pump source,58fs pulses centered at 845nm were generated.The av...A femtosecond Kerr-lens mode-locked Cr:LiSGaF laser based on a compact cavity geometry is demonstrated.With a combination of 488,476,and 458nm lines as a pump source,58fs pulses centered at 845nm were generated.The average output power is 30mW,and time-band product is 0.331,assuming a sech^(2) pulse shape.Neither acousto-modulator nor physical aperture or slit were used in this cavity.展开更多
基金supports from National Natural Science Foundation of China(Grant No.52105498)The science and technology innovation Program of Hunan Province(Grant No.2021RC3074)+2 种基金Advanced Laser Technology Laboratory of Anhui Province(AHL2022KF04)National Key R&D Program of China(Grant No.2023YFB14605500)Changsha Natural Science Foundation(kq2402089).
文摘Combined pulsed laser(CPL),introduced in 1975 for target damage,integrates different lasers to achieve high peak power and pulse energy.However,despite decades of research,CPL remains unused for long-range target damage due to the challenge of maintaining high peak power density over long distances.We note that a potential solution lies in leveraging the air filament generated by femtosecond laser,which can transmit peak power densities higher than 1014 W/cm^(2)under the power clamping effect.To address this,a concept of a femtosecond laser induced air filament-CW CPL for surface damage of ceramics was introduced.We found no surface changes in ceramic targets when irradiated with a CW laser alone.By way of contrast,the target can be penetrated in a very short time(20 ms)with the assistance of the femtosecond laser induced air filament.In this context,we employ high-speed shadow imaging,cross-timescale simulation models and macro-microscopic characterization,to elucidate the CPL damage mechanism.The optimal CPL,combining a 1 mJ femtosecond laser and a 500 W CW laser,yields a damage rate of 1.51×10^(7)μm^(3)/J,representing an improvement of approximately 175%compared to single femtosecond laser ablation and around 59%enhancement compared to coating-assisted CW laser ablation.Furthermore,the efficacy of the proposed femtosecond-CW CPL method is demonstrated in causing penetration damage of ceramic/metal composite material or direct damage of sapphire,showcasing its versatility in damaging applications.Consequently,the femtosecond-CW CPL ablation method presented in this paper holds great promise as a new type of damage method for transparent hard and brittle materials.
基金supported by the National Natural Science Foundation of China(Grant Nos.62227821 and 42461050)the Key Project of the National Institute of Metrology,China(Grant Nos.AKYZD2411 and AKYZD2511-2).
文摘We demonstrate few-cycle pulse generation based on double-stage all-fiber nonlinear pulse compression from a thulium-doped fiber laser at a repetition rate of∼199.74 MHz.The homemade laser provides an average power of 130 mW,serving as the seed for subsequent amplification.After amplification,significant spectral broadening to an octave-spanning bandwidth(1.2 to 2.4μm)is attained through self-phase modulation-dominated nonlinear effects in an ultrahigh numerical aperture fiber and a highly nonlinear fiber.Followed by a two-stage nonlinear compressor,the system directly delivers near transform-limited pulses with a pulse duration of 19.8 fs(2.9 cycles at a central wavelength of 2000 nm)and a pulse energy of 3.37 nJ.To the best of our knowledge,this result is the shortest pulse duration directly generated from a thulium-doped fiber laser.This robust and simplified all-fiber system provides a promising route toward practical mid-infrared frequency comb generation and mid-infrared spectroscopy.
基金Project(52105498) supported by the National Natural Science Foundation of ChinaProject(2021RC3074) supported by the Science and Technology Innovation Program of Hunan Province,China+2 种基金Project(2023YFB4605500) supported by the National Key Research and Development Program of ChinaProject(AHL2022KF04) supported by the Advanced Laser Technology Laboratory of Anhui Province,ChinaProject(kq2402089) supported by the Changsha Natural Science Foundation,China。
文摘High-energy continuous wave(CW)lasers are mostly used in laser damage applications,but efficient laser ablation of transparent materials is challenging due to low optical absorption.Considering the potential of femtosecond(fs)laser-induced air filament for high-peak laser transmission over long distances,femtosecond(fs)laser-induced air filaments are combined with a millisecond(ms)laser to form an fs-ms CPL,enhancing the efficiency of sapphire ablation through synchronized spatial-temporal focusing.Experimental results show that ablation efficiency increases with the ms peak power and duty ratio.Excessive thermal stress leads to fragmentation of the sapphire when the ms duty ratio is over 30%at the peak power of 800 W,or when the peak power is over 500 W at a duty ratio of 100%.Also,the mechanism of high-efficiency damage is revealed through in-situ high-speed imaging.According to it,the ablation process went through 4 stages within 1.5 ms:defect-creating,melting and ablation,spattering,and fragmentation.Finally,the equivalent ablation efficiency of the fs-ms CPL is as high as 1.73×10^(7)μm^(3)/J,about 28 times higher compared to the fs laser only.The CPL damage method explored in this paper can provide theoretical guidance for efficient laser damage of transparent materials.
基金the National Natural Science Foundation of China(52102012)Natural Science Foundation of Anhui Province(2208085QF217)the Fundamental Research Funds for the Central Universities(WK5290000004)。
文摘We demonstrate the growth,thermal,spectroscopy and laser performance of an Er3+doped Gdo.iYo.9AlO3(Er:GYAP)disorder crystal grown by Czochralski method.The crystal with space group Pbnm and lattice parameters of a=0.5185 nm,b=0.5327 nm,c=0.7378 nm,α=β=90°and V=0.203784 nm3 are obtained by fitting powder X-ray diffraction data.The Mohr's hardnesses along three axes are 6.94,7.27,and 7.44.The thermal expansion coefficient of b axis is 4.20×10^(-6)k^(-1)and the density is 5.88 g/cm3.The thermal conductivities are characterized as K_(a)=6.24,K_(b)=5.57,and K_(c)=6.83 W/(m·K).Meanwhile,the refractive index,absorption and emission spectra in triaxial di-rections are determined.Besides,level lifetimes of 4l11/2 and 413/2 are 0.86 and 2.83 ms.Finally,the~2.7μm multiwavelength laser outputs are observed with maximum average power of 628 mW and beam quality factors M_(x)^(2)/M_(y)^(2) of 1.42/1.45.The results prove that the Er:GYAP crystal is a promising gain medium for generating mid-infrared lasers.
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Project supported by the Industrial Technology Development Program,China (Grant No. A1120110023)the National Key Laboratory of Solid-State-Laser Technology,China (Grant No. 9140C040201100C04)
文摘In this paper,we investigate laser cleaning using a flattened top laser to remove paint coating from a metal substrate.Under the irradiation of a flattened top laser,the coating paint of the metal substrate can be removed efficiently by laser induced ablation,stress,and displacement force.The temperature distribution,stress,and displacement are calculated in the coating layer and substrate using finite element analysis.The effects of a Gaussian laser and a flattened top laser and the results of different diameters of laser spot are compared.The investigation shows that the flattened top laser can reduce the substrate damage and enhance the cleaning efficiency.This method meets the need of large area industrial cleaning applications by optimizing the flattened top laser parameters.
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Purpose:To evaluate the clinical efficacy of Pattern Scan Laser Photocoagulator (PASCAL) by observing the efficacy of PASCAL on retinopathy.Methods:A total of 92 patients with retinopathy (121 eyes) who underwent PASCAL between December 2008 and February 2009 in our center were retrospectively analyzed to evaluate the visual acuity changes and recovery conditions of the patients from baseline to posterior to the treatment.The retinopathy included:diabetic retinopathy,ischemic retinal vein occlusion.(IRVO),central serous chorioretinopathy (CSC),retinal periphlebitis (Eales disease) and retinal degeneration /holes.Results:The patients were subject to a 12-month follow up after PASCAL.The visual acuity findings were stated as below:for diabetic retinopathy.(73 eyes),10 eyes had improved visual acuity;55 eyes were stabilized and 8 eyes progressed;for IRVO (13 eyes),4 eyes showed improvement,6 eyes were stabilized and 3 eyes progressed;for CSC (9 eyes),6 eyes were alleviated and 3 eyes progressed;for retinal periphlebitis (5 eyes),2 eyes had enhanced visual acuity and 3 eyes showed stable visual acuity;for retinal degeneration /holes (21 eyes),5 eyes presented improved visu-al acuity,16 eyes were stabilized and no eye progressed.Indirect ophthalmoscopic reexamination confirmed secured blockage by laser spots and favorable absorption of the retinal edema and newborn capillaries.No obvious leakage was observed during fundus fluorescein angiography and no laser-related ocular adverse effect was reported.Conclusion:PASCAL is accurate,effective and well-tolerated.The duration of short laser pulse falls within the safety range,ensuring the stabilization and improvement in the pa-tient's visual acuity.The parameters,long-term efficacy and complications of PASCAL should be further demonstrated by performing long-term clinical trials with larger sample size.
基金Project supported by the National Basic Research Program of China (Grant No. 2006CB806002)the National High Technology Research and Development Program of China (Grant No. 2007AA03Z447)+3 种基金National Natural Science Foundation of China (Grant Nos. 60678012 and 60838004)the Foundation for Key Program of Ministry of Education, China (Grant No. 108032)FANEDD(Grant No. 2007B34)NCET (Grant No. NCET-07-0597)
文摘A Kerr-lens mode-locked Ti：sapphire laser operating in a non-soliton regime is demonstrated. Dispersive wave generation is observed as a result of third order dispersion in the vicinity of zero dispersion. The characteristics of the Ti：sapphire l^ser operating in a positive dispersion regime are presented, where the oscillator directly generates pulses with duration continuously tunable from 0.37 ps to 2.11 ps, and 36 fs pulses are achieved atter extracavity compression. The oscillation is numerically simulated with an extended nonlinear Schr6dinger equation, and the simulation results are in good agreement with the experimental results.
文摘In this paper, results are presented on first application of laser-induced breakdown spectroscopy （LIBS） technique for quantitative determination of Mg concentration in alpha-olefins. It is demonstrated that this technique gives accuracies in Mg concentrations which are comparable with those of traditional methods, as ICP-OES, in short times and without need for sample preparation. Limits of detection for Mg of the order of 500 ppb are demonstrated. Moreover, a brief discussion about the realization of orooer calibration curves and the definition of the limit of detection （LOD） is reoorted.
基金the National Natural Science Foundation of China(Nos.11104201 and 51376013)the Open Fund of Key Laboratory of Opto-electronic Information Technology,Ministry of Education,in Tianjin Universitythe China National Scholarship Fund
文摘Based on the normal pulsed laser ablation method,femtosecond pulsed laser deposition(fs-PLD)is adopted in vacuum for the production of TiO2nanoparticle-assembled films.We study the morphology and electronic characteristics of TiO2nanoparticle-assembled films deposited at different oxygen background gas pressures from high vacuum(~10-4Pa)to 100 Pa and different deposition time.Our results show that TiO2nanoparticle-assembled films obtained in high vacuum present both a mixture with rutile phase and anatase phase and a pure rutile phase.At the same time,there are more mesoporous structures in the film after annealing,which is beneficial for the enhancement of photocatalytic activity.In water splitting experiment,part of the TiO2nanoparticle-assembled films embedded with a small mass fraction of CdS nanoparticles(~5%)present an interesting photocurrent enhancement with a maximum value of^0.2mA/cm2under a solar simulator.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10834008)the State Key Development Program for Basic Research of China (Grant No. 2006CB806004)
文摘Forward fast protons are generated by the moderate-intensity laser-foil interaction. Protons with maximum energy 190 keV are measured by using magnetic spectrometer and CR-39 solid state track detectors along the direction normal to the rear surface. The experimental results are also modeled by the paxticle-in-cell method, investigating the timevarying electron temperature and the rear sheath field. The temporal and spatial structure of the sheath electrical field, revealed in the simulation, suggests that these protons are accelerated by target normal sheath acceleration （TNSA） mechanism.
文摘Since the first laser was invented,the pursuit of high-energy lasers(HELs)has always been enthusiastic.The first revolution of HELs was pushed by the fusion of laser and aerospace in the 1960s,with the chemical rocket engines giving fresh impetus to the birth of gas flow and chemical lasers,which finally turned megawatt lasers from dream into reality.Nowadays,the development of HELs has entered the age of electricity as well as the rocket engines.The properties of current electric rocket engines are highly consistent with HELs’goals,including electrical driving,effective heat dissipation,little medium consumption and extremely light weight and size,which inspired a second fusion of laser and aerospace and motivated the exploration for potential HELs.As an exploratory attempt,a new configuration of diode pumped metastable rare gas laser was demonstrated,with the gain generator resembling an electric rocket-engine for improved power scaling ability.
基金The research was performed at the Laser Thermal Laboratory by Drs David J Hwang,Sang-gil Ryu,Eunpa Kim,Jung Bin In,and the current students,Letian Wang,Yoonsoo Rho and Matthew Eliceiri.Professors Andrew M Minor,Junqiao Wu,Oscar D Dubon,Drs Bin Xiang,Frances I Allen,and Changhyun Ko of UCB Materials Science and Engineering,and Dr Carlo Carraro of UCB Chem.Engineering contributed to the work.The research was supported by DARPA/MTO under TBN grant N66001-08-1-2041,the US Department of Energy SBIR grant(DE-FG02-07ER84813),Samsung GRO,and NSF CMMI-1363392.The in situ experiments were performed at the National Center for Electron Microscopy at the Lawrence Berkeley National Laboratory,which is supported by the Office of Science,Office of Basic Energy Sciences,Scientific User Facilities Division,of the US Department of Energy under Contract No.DE-AC02-05CH11231.The laser-induced nanowire growth and doping was conducted on the LACVD apparatus in the UC Berkeley Marvell Nanofabrication Laboratory.
文摘This article summarizes work at the Laser Thermal Laboratory and discusses related studies on the laser synthesis and functionalization of semiconductor nanostructures and two-dimensional(2D)semiconductor materials.Research has been carried out on the laser-induced crystallization of thin films and nanostructures.The in situ transmission electron microscopy(TEM)monitoring of the crystallization of amorphous precursors in nanodomains is discussed herein.The directed assembly of silicon nanoparticles and the modulation of their optical properties by phase switching is presented.The vapor-liquid-solid mechanism has been adopted as a bottom-up approach in the synthesis of semiconducting nanowires(NWs).In contrast to furnace heating methods,laser irradiation offers high spatial selectivity and precise control of the heating mechanism in the time domain.These attributes enabled the investigation of NW nucleation and the early stage of nanostructure growth.Site-and shape-selective,on-demand direct integration of oriented NWs was accomplished.Growth of discrete silicon NWs with nanoscale location selectivity by employing near-field laser illumination is also reported herein.Tuning the properties of 2D transition metal dichalcogenides(TMDCs)by modulating the free carrier type,density,and composition can offer an exciting new pathway to various practical nanoscale electronics.In situ Raman probing of laser-induced processing of TMDC flakes was conducted in a TEM instrument.
文摘We report on the biodegradation of pure hydrocarbons and chemotaxis towards these compounds by an isolated chlorophenol degrader,Pseudomonas strain H.The biochemical and phylogenetic analysis of the 16S rDNA sequence identified Pseudomonas strain H as having 99.56% similarity with P.aeruginosa PA01.This strain was able to degrade n-hexadecane,1-undecene,1-nonene,1-decene,1-dodecene and kerosene.It grew in the presence of 1-octene,while this hydrocarbons is toxic to other hydrocarbons degraders.Pseudomonas strain H was also chemotactic towards n-hexadecane,kerosene,1-undecene and 1-dodecene.These results show that this Pseudomonas strain H is an attractive candidate for hydrocarbon-containing wastewater bioremediation in controlled environments.Since the classical standard techniques for detecting chemotaxis are not efficient at low bacterial concentrations,we demonstrate the use of the dynamic speckle laser method,which is simple and inexpensive,to confirm bacterial chemotaxis at low cell concentrations （less than 105 colony-forming unit per millilitre （CFU/mL）） when hydrocarbons are the attractants.
基金Project supported by the Key Grant Project of the Ministry of Education of the People’s Republic of China (Grant No 10410)National Natural Science Fundation of China (Grant No 60572168)Science Research Start-up Fund of Civil Aviation University of China (Grant No qd02x11)
文摘The morphologies of the deposited dots on the 40 nm-thick copper film by the femtosecond laser-induced forward transfer that depend on the irradiated laser fluence have been studied, and the variations of orderliness of the diameter of deposited dots on the quartz substrate and forward ablated dot on the donor substrate with increasing pulse fluence have been obtained experimentally. The experimental results show that a thinner copper film would generate larger-sized ablated dot and deposited dot at the threshold fluence for transfer. By x-ray diffraction measurement, it is demonstrated that the crystal form of the transferred copper films is unaltered and the size of the crystallites is diminished.
基金Supported by the National Basic Research Programme of China under Grant No 2006CB806004, and the National Natural Science Foundation of China under Grant No 10334110.
文摘We investigate the kinetic energy of expanding plasma of a solid target heated by a ultra-short and ultra-intense laser pulse and the efllciency of energy coupling between the ultra-intense laser pulse and the solid target, in order to increase the utilization ratio of laser energy and to raise the neutron generation farther. Some new ideas about improving the energy utilization by head-on collision~, between the expanding plasmas are proposed. The significance is the raise of generation of shorter duration neutron, of the order of picoseconds, which allows for an increase of energy resolution in time-of-flight experiments and also for the investigation of the dynamics of nuclear processes with high temporal resolution.
基金from National Natural Science Foundation of China(NSFC)81571719,61322502Open Project of State Key Laboratory of Modern Optical Instrumentation,Zhejiang University,and Program for Changjiang Scholars and Innovative Research Team in Uni-versity IRT13033.
文摘Usually,only focused femtosecond(fs)lasers at near-infrared(NIR)range can induce photo-damage to transparent cells,making it difficult to treat large amount of cells by such optical methods for photostimulation.In this study,we clarify the mechanism of photodamage to cells that are co-cultured with gold nanorods(GNRs)by fs laser.The pulse duration and repetition rate of the fs laser play a key role in cell damage suggesting that the heat accumulation con-tributes to the major part for the cell damage rather than the high peak power which mainly determines the efficiency of multiphoton excitation.We further show that cellular Ca^(2+)can also be released in this scheme,but the process is more sensitive to peak power.Our results can provide a large-scale GNR-mediated photostimulation for cell signaling modulation.
基金Supported in part by K.C.Wong Education Foundation in Hong Kong and Post-doctoral Foundation of China.
文摘We used transition radiation techniques instead of the original phosphor targets to improve the electronic beam diagnostic system at Beijing Free Electron Laser.The beam profile,size(3.3×2.4mm),position and divergence angle(σrms=2.5mrad)in transverse have been obtained from optical transition radiation.We also present the experimental set-up and some preliminary results.
基金Supported by the National Natural Science Foundation of China under Grant No.69608002the Excellent Young Teacher's Foundation of the Ministry of Education。
文摘A femtosecond Kerr-lens mode-locked Cr:LiSGaF laser based on a compact cavity geometry is demonstrated.With a combination of 488,476,and 458nm lines as a pump source,58fs pulses centered at 845nm were generated.The average output power is 30mW,and time-band product is 0.331,assuming a sech^(2) pulse shape.Neither acousto-modulator nor physical aperture or slit were used in this cavity.
