Spatial patterns are a significant characteristic of lasers.The knowledge of spatial patterns of structured laser beams is rapidly expanding,along with the progress of studies on laser physics and technology.Particula...Spatial patterns are a significant characteristic of lasers.The knowledge of spatial patterns of structured laser beams is rapidly expanding,along with the progress of studies on laser physics and technology.Particularly in the last decades,owing to the in-depth attention on structured light with multiple degrees of freedom,the research on spatial and spatiotemporal structures of laser beams has been promptly developed.Such beams have hatched various breakthroughs in many fields,including imaging,microscopy,metrology,communication,optical trapping,and quantum information processing.Here,we would like to provide an overview of the extensive research on several areas relevant to spatial patterns of structured laser beams,from spontaneous organization to multiple transformations.These include the early theory of beam pattern formation based on the Maxwell–Bloch equations,the recent eigenmodes superposition theory based on the time-averaged Helmholtz equations,the beam patterns extension of ultrafast lasers to the spatiotemporal beam structures,and the structural transformations in the nonlinear frequency conversion process of structured beams.展开更多
To improve the measurement accuracy of structured laser for inner surface dimensions of a deep hole, a new method to extract the laser stripe center line is proposed. An improved adaptive genetic algorithm that can co...To improve the measurement accuracy of structured laser for inner surface dimensions of a deep hole, a new method to extract the laser stripe center line is proposed. An improved adaptive genetic algorithm that can converge rapidly and search the global optimum is used to determine the threshold for the laser stripe segmentation. And then NURBS interpolation which has a good local control capability is adopted to extract the laser stripe center line. Experiments show that the extracted laser stripe center line is stable and the diameter of the deep hole can be measured accurately.展开更多
Traditional electrode manufacturing for lithium-ion batteries is well established,reliable,and has already reached high processing speeds and improvements in production costs.For modern electric vehicles,however,the n...Traditional electrode manufacturing for lithium-ion batteries is well established,reliable,and has already reached high processing speeds and improvements in production costs.For modern electric vehicles,however,the need for batteries with high gravimetric and volumetric energy densities at cell level is increasing;and new production concepts are required for this purpose.During the last decade,laser processing of battery materials emerged as a promising processing tool for either improving manufacturing flexibility and product reliability or enhancing battery performances.Laser cutting and welding already reached a high level of maturity and it is obvious that in the near future they will become frequently implemented in battery production lines.This review focuses on laser texturing of electrode materials due to its high potential for significantly enhancing battery performances beyond state-of-the-art.Technical approaches and processing strategies for new electrode architectures and concepts will be presented and discussed with regard to energy and power density requirements.The boost of electrochemical performances due to laser texturing of energy storage materials is currently proven at the laboratory scale.However,promising developments in high-power,ultrafast laser technology may push laser structuring of batteries to the next technical readiness level soon.For demonstration in pilot lines adapted to future cell production,process upscaling regarding footprint area and processing speed are the main issues as well as the economic aspects with regards to CapEx amortization and the benefits resulting from the next generation battery.This review begins with an introduction of the three-dimensional battery and thick film concept,made possible by laser texturing.Laser processing of electrode components,namely current collectors,anodes,and cathodes will be presented.Different types of electrode architectures,such as holes,grids,and lines,were generated;their impact on battery performances are illustrated.The usage of high-energy materials,which are on the threshold of commercialization,is highlighted.Battery performance increase is triggered by controlling lithium-ion diffusion kinetics in liquid electrolyte filled porous electrodes.This review concludes with a discussion of various laser parameter tasks for process upscaling in a new type of extreme manufacturing.展开更多
Laser-structuring is an effective method to promote ion diffusion and improve the performance of lithium-ion battery(LIB)electrodes.In this work,the effects of laser structuring parameters(groove pitch and depth)on th...Laser-structuring is an effective method to promote ion diffusion and improve the performance of lithium-ion battery(LIB)electrodes.In this work,the effects of laser structuring parameters(groove pitch and depth)on the fundamental characteristics of LIB electrode,such as interfacial area,internal resistances,material loss and electrochemical performance,are investigated,LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2) cathodes were structured by a femtosecond laser by varying groove depth and pitch,which resulted in a material loss of 5%-14%and an increase of 140%-260%in the in terfacial area between electrode surface and electrolyte.It is shown that the importance of groove depth and pitch on the electrochemical performance(specific capacity and areal discharge capacity)of laser-structured electrode varies with current rates.Groove pitch is more im porta nt at low current rate but groove depth is at high curre nt rate.From the mapping of lithium concentration within the electrodes of varying groove depth and pitch by laser-induced breakdown spectroscopy,it is verified that the groove functions as a diffusion path for lithium ions.The ionic,electronic,and charge transfer resistances measured with symmetric and half cells showed that these internal resistances are differently affected by laser structuring parameters and the changes in porosity,ionic diffusion and electronic pathways.It is demonstrated that the laser structuring parameters for maximum electrode performance and minimum capacity loss should be determined in consideration of the main operating conditions of LIBs.展开更多
We report an experimental investigation on laser ablation and associated surface structuring of CdZnTe by femtosecond Ti:Sa laser pulses(laser wavelengthλ≈800 nm,≈35 fs,10 Hz),in air.By exploiting different static ...We report an experimental investigation on laser ablation and associated surface structuring of CdZnTe by femtosecond Ti:Sa laser pulses(laser wavelengthλ≈800 nm,≈35 fs,10 Hz),in air.By exploiting different static irradiation conditions,the fluence threshold and the incubation effect in CdZnTe are estimated.Interestingly,surface treatment with a low laser fluence(laser pulse energy E≈5-10_μJ)and number of shots(5<N<50)show the formation of well-defined cracks in the central part of the shallow crater,which is likely associated to a different thermal expansion coefficients of Te inclusions and matrix during the sample heating and cooling processes ensuing femtosecond laser irradiation.Irradiation with a larger number of pulses(N≈500,1000)with higher pulse energies(E≈30-50μJ)results in the formation of welldefined laser-induced periodic surface structures(LIPSS)in the outskirts of the main crater,where the local fluence is well below the material ablation threshold.Both low spatial frequency and high spatial frequency LIPSS perpendicular to the laser polarization are found together and separately depending on the irradiation condition.These are ascribed to a process of progressive aggregation of randomly distributed nanoparticles produced during laser ablation of the deep crater in the region of the target irradiated by a fluence below the ablation threshold with many laser pulses.展开更多
We report our recent progress of investigations on InGaN-based blue-violet laser diodes （LDs）. The roomtemperature （RT） cw operation lifetime of LDs has extended to longer than 15.6 h. The LD structure was grown o...We report our recent progress of investigations on InGaN-based blue-violet laser diodes （LDs）. The roomtemperature （RT） cw operation lifetime of LDs has extended to longer than 15.6 h. The LD structure was grown on a c-plane free-standing （FS） GaN substrate by metal organic chemical vapor deposition （MOCVD）. The typical threshold current and voltage of LD under RT cw operation are 78 mA and 6.8 V, respectively. The experimental analysis of degradation of LD performances suggests that after aging treatment, the increase of series resistance and threshold current can be mainly attributed to the deterioration of p-type ohmic contact and the decrease of internal quantum efticiency of multiple quantum well （MQW）, respectively.展开更多
In the comparison of damage modifications, absorption measurement and energy dispersive x-ray analysis, the effect of vacuum on the laser-induced damage of anti-reflection coatings is analyzed. It is found that vacuum...In the comparison of damage modifications, absorption measurement and energy dispersive x-ray analysis, the effect of vacuum on the laser-induced damage of anti-reflection coatings is analyzed. It is found that vacuum decreases the laser-induced damage threshold of the films. The low laser-induced damage threshold in vacuum environments as opposed to air environments is attributed to water absorption and the formation of the O/Si, O/Zr sub-stoichiometry in the course of laser irradiation.展开更多
In this paper, an asymmetric array structure of space laser communication receiver is proposed. This structure can greatly reduce alignment requirement, and lighten the signal strength jitter caused by atmospheric tur...In this paper, an asymmetric array structure of space laser communication receiver is proposed. This structure can greatly reduce alignment requirement, and lighten the signal strength jitter caused by atmospheric turbulence. A prototype of the proposed structure is fabricated and a 2.5 Mbit/s on-off keying(OOK) modulated demonstration link over 40 m free space is built. This asymmetric array structure can effectively collect optical signal while rotating in a window angle of ±17°, and the bit error ratio(BER) keeps zero.展开更多
The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control...The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control of the multi-photon absorption by the phase, amplitude and polarization modulation, but the coherent features of the multi-photon absorption depending on the energy level structure, the laser spectrum bandwidth and laser central frequency still lack in-depth systematic research. In this work, we further explore the coherent features of the resonance-mediated two-photon absorption in a rubidium atom by varying the energy level structure, spectrum bandwidth and central frequency of the femtosecond laser field. The theoretical results show that the change of the intermediate state detuning can effectively influence the enhancement of the near-resonant part, which further affects the transform-limited （TL）-normalized final state population maximum. Moreover, as the laser spectrum bandwidth increases, the TL-normalized final state population maximum can be effectively enhanced due to the increase of the enhancement in the near-resonant part, but the TL-normalized final state population maximum is constant by varying the laser central frequency. These studies can provide a clear physical picture for understanding the coherent features of the resonance-mediated two-photon absorption, and can also provide a theoretical guidance for the future applications.展开更多
We report the molecular beam epitaxy growth of 1.3 μm InAs/GaAs quantum-dot （QD） lasers with high characteristic temperature T0. The active region of the lasers consists of five-layer InAs QDs with p-type modulatio...We report the molecular beam epitaxy growth of 1.3 μm InAs/GaAs quantum-dot （QD） lasers with high characteristic temperature T0. The active region of the lasers consists of five-layer InAs QDs with p-type modulation doping. Devices with a stripe width of 4 μm and a cavity length of 1200 μm are fabricated and tested in the pulsed regime under different temperatures. It is found that T0 of the QD lasers is as high as 532 K in the temperature range from 10°C to 60°C. In addition, the aging test for the lasers under continuous wave operation at 100°C for 72 h shows almost no degradation, indicating the high crystal quality of the devices.展开更多
Laser induced periodic surface structures(LIPSS)represent a kind of top down approach to produce highly reproducible nano/microstructures without going for any sophisticated process of lithography.This method is much ...Laser induced periodic surface structures(LIPSS)represent a kind of top down approach to produce highly reproducible nano/microstructures without going for any sophisticated process of lithography.This method is much simpler and cost effective.In this work,LIPSS on Si surfaces were generated using femtosecond laser pulses of 800 nm wavelength.Photocatalytic substrates were prepared by depositing TiO2 thin films on top of the structured and unstructured Si wafer.The coatings were produced by sputtering from a Ti target in two different types of oxygen atmospheres.In first case,the oxygen pressure within the sputtering chamber was chosen to be high(3×10^–2 mbar)whereas it was one order of magnitude lower in second case(2.1×10^–3 mbar).In photocatalytic dye decomposition study of Methylene blue dye it was found that in the presence of LIPSS the activity can be enhanced by 2.1 and 3.3 times with high pressure and low pressure grown TiO2 thin films,respectively.The increase in photocatalytic activity is attributed to the enlargement of effective surface area.In comparative study,the dye decomposition rates of TiO2 thin films grown on LIPSS are found to be much higher than the value for standard reference thin film material Pilkington Activ^TM.展开更多
The structural deformation of NO2 group induced by an intense femtosecond laser field of liquid nitromethane（NM）molecule is detected by time-and frequency-resolved coherent anti-Stokes Raman spectroscopy（CARS） tec...The structural deformation of NO2 group induced by an intense femtosecond laser field of liquid nitromethane（NM）molecule is detected by time-and frequency-resolved coherent anti-Stokes Raman spectroscopy（CARS） technique with the intense pump laser. Here, we present the mechanism of molecular alignment and deformation. The CARS spectra and its FFT spectra of liquid NM show that the NO2 torsional mode couples with the CN symmetric stretching mode and that the NO2 group undergoes ultrafast structural deformation with a relaxation time of 195 fs. The frequency of the NO2 torsional mode in liquid NM（50.8±0.3 cm^-1） at room temperature is found. Our results prove the structural deformation of two groups in liquid NM molecule occur simultaneously in the intense laser field.展开更多
The surface of Ni_（61）Nb_（39） crystalline ingot was treated by laser surface melting with different processing parameters.A fully amorphous layer with a thickness of approximately 10μm could be produced on the to...The surface of Ni_（61）Nb_（39） crystalline ingot was treated by laser surface melting with different processing parameters.A fully amorphous layer with a thickness of approximately 10μm could be produced on the top surface under optimal parameters.An amorphous-crystalline composite layer with the depth from 10 to 50μm,consisting of amorphous matrix and intermetallic phases of Ni_3 Nb and Ni_6Nb_7,could be formed.The micro-hardness（about 831HV）of the treated surface was remarkably improved by nearly 100% compared with the value of the crystalline substrate caused by the formation of the fully amorphous structure.A finite volume simulation was adopted to evaluate the temperature distribution in the laser-affected zone of Ni_（61）Nb_（39） alloys and to reveal the mechanism of glass formation in the laser-affected zone.展开更多
Engineering ultrashort laser pulses is crucial for advancing fundamental research fields and applications.Controlling their spatiotemporal behavior,tailored to specific applications,can unlock new experimental capabil...Engineering ultrashort laser pulses is crucial for advancing fundamental research fields and applications.Controlling their spatiotemporal behavior,tailored to specific applications,can unlock new experimental capabilities.However,achieving this control is particularly challenging due to the difficulty in independently structuring their intensity and spatial phase distributions,given their polychromatic bandwidth.This article addresses this challenge by presenting a technique for generating flying structured laser pulses with tunable spatiotemporal behavior.We developed a comprehensive approach to directly design and govern these laser pulses.This method elucidates the role jointly played by the pulse's spatiotemporal couplings and its prescribed phase gradient in governing the pulse dynamics.It evidences that the often-overlooked design of the phase gradient is indeed essential for achieving programmable spatiotemporal control of the pulses.By tailoring the prescribed phase gradient,we demonstrate the creation of,to our knowledge,novel families of flying structured laser pulses that travel at the speed of light in helical spring and vortex multi-ring forms of different geometries.The achieved control over the dynamics of their intensity peaks and wavefronts is analyzed in detail.For instance,the intensity peak can be configured as a THz rotating light spot or shaped as a curve,enabling simultaneous substrate illumination at rates of tens of THz,far exceeding the MHz rates typically used in laser material processing.Additionally,the independent manipulation of the pulse wavefronts allows local tuning of the orbital angular momentum density carried by the beam.Together,these advancements unveil advantageous capabilities that have been sought after for many years,especially in ultrafast optics and light-matter interaction research.展开更多
This review examines the state-of-the-art in spatial manipulation of ultrafast laser processing using dynamic light modulators,with a particular focus on liquid crystal-based systems.We discuss phase modulation strate...This review examines the state-of-the-art in spatial manipulation of ultrafast laser processing using dynamic light modulators,with a particular focus on liquid crystal-based systems.We discuss phase modulation strategies and highlight the current limitations and challenges in surface and bulk processing.Specifically,we emphasize the delicate balance between high-fidelity beam shaping and energy efficiency,both critical for surface and bulk processing applications.Given the inherent physical limitations of spatial light modulators such as spatial resolution,fill factor,and phase modulation range.We explore techniques developed to bridge the gap between desired intensity distributions and actual experimental beam profiles.We present various laser light modulation technologies and the main algorithmic strategies for obtaining modulation patterns.The paper includes application examples across a wide range of fields,from surgery to surface structuring,cutting,bulk photo-inscription of optical functions,and additive manufacturing,highlighting the significant enhancements in processing speed and precision due to spatial beam shaping.The diverse applications and the technological limitations underscore the need for adapted modulation pattern calculation methods.We discuss several advancements addressing these challenges,involving both experimental and algorithmic developments,including the recent incorporation of artificial intelligence.Additionally,we cover recent progress in phase and pulse front control based on spatial modulators,which introduces an extra control parameter for light excitation with high potential for achieving more controlled processing outcomes.展开更多
The mathematical expression of the electron diffusion and drift length LDE of exponential doping photocathode is deduced. In the quantum efficiency equation of the reflection-mode uniform doping cathode, substituting ...The mathematical expression of the electron diffusion and drift length LDE of exponential doping photocathode is deduced. In the quantum efficiency equation of the reflection-mode uniform doping cathode, substituting LDE for LD, the equivalent quantum efficiency equation of the reflection-mode exponential doping cathode is obtained. By using the equivalent equation, theoretical simulation and experimental analysis shows that the equivalent index formula and formula-doped cathode quantum efficiency results in line. The equivalent equation avoids complicated calculation, thereby simplifies the process of solving the quantum efficiency of exponential doping photocathode.展开更多
We report on the growth and fabrication of deep ultraviolet （DUV） light emitting diodes （LEDs） on an AIN template which was grown on a pulsed atomic-layer epitaxial buffer layer. Threading dislocation densities i...We report on the growth and fabrication of deep ultraviolet （DUV） light emitting diodes （LEDs） on an AIN template which was grown on a pulsed atomic-layer epitaxial buffer layer. Threading dislocation densities in the AlN layer are greatly decreased with the introduction of this buffer layer. The crystalline quality of the AlGaN epilayer is further improved by using a low-temperature GaN interlayer between AlGaN and AlN. Electroluminescences of different DUV-LED devices at a wavelength of between 262 and 317nm are demonstrated. To improve the hole concentration of p-type AlGaN, Mg-doping with trimethylindium assistance approach is performed. It is found that the serial resistance of DUV-LED decreases and the performance of DUV-LED such as EL properties is improved.展开更多
Ce3＋/Eu2＋ codoped LiSrBO3 phosphor is synthesized, and its luminescent characteristics are investigated. LiSrBO3：Ce3＋,Eu2＋ phosphor exhibits varied hues from blue to white and eventually to yellow by resonance-ty...Ce3＋/Eu2＋ codoped LiSrBO3 phosphor is synthesized, and its luminescent characteristics are investigated. LiSrBO3：Ce3＋,Eu2＋ phosphor exhibits varied hues from blue to white and eventually to yellow by resonance-type energy transfer from Ce3＋ ion to Eu2＋ ion and tuning the relative proportion of Ce3＋/Eu2＋ properly. Energy transfer mechanism in LiSrBOa：Ce3＋, Eu2＋ phosphor is dominated by the dipole-dipole interaction, and the critical distance of the energy transfer is estimated to be about 2 nm by both spectral overlap and concentration quenching methods. Under UV radiation, white light is generated by coupling 436 and 565nm emission bands attributed to Ce3＋ and Eu2＋ radiations, respectively.展开更多
A type of multi-core Er-doped photosensitive silica optical fiber （MC-EDPF） is proposed and fabricated, in which a high consistency Er-doped core is surrounded by six high consistency Ge-doped cores. The multi-core ...A type of multi-core Er-doped photosensitive silica optical fiber （MC-EDPF） is proposed and fabricated, in which a high consistency Er-doped core is surrounded by six high consistency Ge-doped cores. The multi-core design can overcome the difficulties encountered in the design and fabrication of single-core EDPFs through a modified chemical vapor deposition method combined with solution doping technology, and there is a conflict between high consistency Er doping and high consistency Ce doping. The absorption of MC-EDPFs achieved 15.876dB/m at 1550mm and lOdB/m at 98Ohm. The refleetivity of the fiber Bragg gratings （FBCs） written directly on the MC-EDPFs is as much as 96.84%.展开更多
Silica microspheres self-assembled in glass capillary are investigated. Monodisperse silica microsphere dispersions in diameter 320nm are self-organized into a bulk cylindrical colloidal crystal by evaporation induced...Silica microspheres self-assembled in glass capillary are investigated. Monodisperse silica microsphere dispersions in diameter 320nm are self-organized into a bulk cylindrical colloidal crystal by evaporation induced nucleation and crystallization. The resulting colloidal crystals are characterized by optical microscopy and scanning electronic microscopy （SEM）, and the SEM images show these crystals dominate in fcc lattice with its （111） crystallographic axis as longitudinal. The colloidal crystal filled capillary is packaged into a heat-shrink plastic tube and a fiber measurement system is designed to measure the optical property of colloidal bulk in capillary. It is found that an appreciable bandgap appears at wavelength 686 nm from the transmission spectroscopy, which is consistent with the theoretical estimation. A considerable photonic band gap of up to -10 dB and a steep photonic band edge of up to 0.25 dB/nm indicate that silica microspheres are promising for implementing optical filter applications in fiber systems.展开更多
文摘Spatial patterns are a significant characteristic of lasers.The knowledge of spatial patterns of structured laser beams is rapidly expanding,along with the progress of studies on laser physics and technology.Particularly in the last decades,owing to the in-depth attention on structured light with multiple degrees of freedom,the research on spatial and spatiotemporal structures of laser beams has been promptly developed.Such beams have hatched various breakthroughs in many fields,including imaging,microscopy,metrology,communication,optical trapping,and quantum information processing.Here,we would like to provide an overview of the extensive research on several areas relevant to spatial patterns of structured laser beams,from spontaneous organization to multiple transformations.These include the early theory of beam pattern formation based on the Maxwell–Bloch equations,the recent eigenmodes superposition theory based on the time-averaged Helmholtz equations,the beam patterns extension of ultrafast lasers to the spatiotemporal beam structures,and the structural transformations in the nonlinear frequency conversion process of structured beams.
基金the Excellent Young Teacher Foundation from Ministry of Education (203078)
文摘To improve the measurement accuracy of structured laser for inner surface dimensions of a deep hole, a new method to extract the laser stripe center line is proposed. An improved adaptive genetic algorithm that can converge rapidly and search the global optimum is used to determine the threshold for the laser stripe segmentation. And then NURBS interpolation which has a good local control capability is adopted to extract the laser stripe center line. Experiments show that the extracted laser stripe center line is stable and the diameter of the deep hole can be measured accurately.
基金The research to anode material development received funding from the German Research Foundation(DFG,project No.392322200)the development of cathode materials and upscaling strategies was funded by the Federal Ministry of Education and Research(Project NextGen-3DBat,03XP0198F).
文摘Traditional electrode manufacturing for lithium-ion batteries is well established,reliable,and has already reached high processing speeds and improvements in production costs.For modern electric vehicles,however,the need for batteries with high gravimetric and volumetric energy densities at cell level is increasing;and new production concepts are required for this purpose.During the last decade,laser processing of battery materials emerged as a promising processing tool for either improving manufacturing flexibility and product reliability or enhancing battery performances.Laser cutting and welding already reached a high level of maturity and it is obvious that in the near future they will become frequently implemented in battery production lines.This review focuses on laser texturing of electrode materials due to its high potential for significantly enhancing battery performances beyond state-of-the-art.Technical approaches and processing strategies for new electrode architectures and concepts will be presented and discussed with regard to energy and power density requirements.The boost of electrochemical performances due to laser texturing of energy storage materials is currently proven at the laboratory scale.However,promising developments in high-power,ultrafast laser technology may push laser structuring of batteries to the next technical readiness level soon.For demonstration in pilot lines adapted to future cell production,process upscaling regarding footprint area and processing speed are the main issues as well as the economic aspects with regards to CapEx amortization and the benefits resulting from the next generation battery.This review begins with an introduction of the three-dimensional battery and thick film concept,made possible by laser texturing.Laser processing of electrode components,namely current collectors,anodes,and cathodes will be presented.Different types of electrode architectures,such as holes,grids,and lines,were generated;their impact on battery performances are illustrated.The usage of high-energy materials,which are on the threshold of commercialization,is highlighted.Battery performance increase is triggered by controlling lithium-ion diffusion kinetics in liquid electrolyte filled porous electrodes.This review concludes with a discussion of various laser parameter tasks for process upscaling in a new type of extreme manufacturing.
基金supported by a GIST Research Institute(GRI)grant funded by the GIST in 2021supported by the Korea In stitute for Advancement of Tech no logy(KIAT)grant funded by the Korea Government(MOTIE).(P0008763,The Competency Development Program for Industry Specialist.)。
文摘Laser-structuring is an effective method to promote ion diffusion and improve the performance of lithium-ion battery(LIB)electrodes.In this work,the effects of laser structuring parameters(groove pitch and depth)on the fundamental characteristics of LIB electrode,such as interfacial area,internal resistances,material loss and electrochemical performance,are investigated,LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2) cathodes were structured by a femtosecond laser by varying groove depth and pitch,which resulted in a material loss of 5%-14%and an increase of 140%-260%in the in terfacial area between electrode surface and electrolyte.It is shown that the importance of groove depth and pitch on the electrochemical performance(specific capacity and areal discharge capacity)of laser-structured electrode varies with current rates.Groove pitch is more im porta nt at low current rate but groove depth is at high curre nt rate.From the mapping of lithium concentration within the electrodes of varying groove depth and pitch by laser-induced breakdown spectroscopy,it is verified that the groove functions as a diffusion path for lithium ions.The ionic,electronic,and charge transfer resistances measured with symmetric and half cells showed that these internal resistances are differently affected by laser structuring parameters and the changes in porosity,ionic diffusion and electronic pathways.It is demonstrated that the laser structuring parameters for maximum electrode performance and minimum capacity loss should be determined in consideration of the main operating conditions of LIBs.
文摘We report an experimental investigation on laser ablation and associated surface structuring of CdZnTe by femtosecond Ti:Sa laser pulses(laser wavelengthλ≈800 nm,≈35 fs,10 Hz),in air.By exploiting different static irradiation conditions,the fluence threshold and the incubation effect in CdZnTe are estimated.Interestingly,surface treatment with a low laser fluence(laser pulse energy E≈5-10_μJ)and number of shots(5<N<50)show the formation of well-defined cracks in the central part of the shallow crater,which is likely associated to a different thermal expansion coefficients of Te inclusions and matrix during the sample heating and cooling processes ensuing femtosecond laser irradiation.Irradiation with a larger number of pulses(N≈500,1000)with higher pulse energies(E≈30-50μJ)results in the formation of welldefined laser-induced periodic surface structures(LIPSS)in the outskirts of the main crater,where the local fluence is well below the material ablation threshold.Both low spatial frequency and high spatial frequency LIPSS perpendicular to the laser polarization are found together and separately depending on the irradiation condition.These are ascribed to a process of progressive aggregation of randomly distributed nanoparticles produced during laser ablation of the deep crater in the region of the target irradiated by a fluence below the ablation threshold with many laser pulses.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60976045, 60506001, 60776047 and 60836003, and the National Basic Research Program of China under Grant No 2007CB936700.
文摘We report our recent progress of investigations on InGaN-based blue-violet laser diodes （LDs）. The roomtemperature （RT） cw operation lifetime of LDs has extended to longer than 15.6 h. The LD structure was grown on a c-plane free-standing （FS） GaN substrate by metal organic chemical vapor deposition （MOCVD）. The typical threshold current and voltage of LD under RT cw operation are 78 mA and 6.8 V, respectively. The experimental analysis of degradation of LD performances suggests that after aging treatment, the increase of series resistance and threshold current can be mainly attributed to the deterioration of p-type ohmic contact and the decrease of internal quantum efticiency of multiple quantum well （MQW）, respectively.
基金Supported by the National Natural Science Foundation of China under Grant No 60708004.
文摘In the comparison of damage modifications, absorption measurement and energy dispersive x-ray analysis, the effect of vacuum on the laser-induced damage of anti-reflection coatings is analyzed. It is found that vacuum decreases the laser-induced damage threshold of the films. The low laser-induced damage threshold in vacuum environments as opposed to air environments is attributed to water absorption and the formation of the O/Si, O/Zr sub-stoichiometry in the course of laser irradiation.
基金supported by the National Natural Science Foundation of China (Nos.61674142 and 62041502)。
文摘In this paper, an asymmetric array structure of space laser communication receiver is proposed. This structure can greatly reduce alignment requirement, and lighten the signal strength jitter caused by atmospheric turbulence. A prototype of the proposed structure is fabricated and a 2.5 Mbit/s on-off keying(OOK) modulated demonstration link over 40 m free space is built. This asymmetric array structure can effectively collect optical signal while rotating in a window angle of ±17°, and the bit error ratio(BER) keeps zero.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51132004,11474096 and 11604199the Science and Technology Commission of Shanghai Municipality under Grant No 14JC1401500the Higher Education Key Program of He'nan Province under Grant Nos 17A140025 and 16A140030
文摘The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control of the multi-photon absorption by the phase, amplitude and polarization modulation, but the coherent features of the multi-photon absorption depending on the energy level structure, the laser spectrum bandwidth and laser central frequency still lack in-depth systematic research. In this work, we further explore the coherent features of the resonance-mediated two-photon absorption in a rubidium atom by varying the energy level structure, spectrum bandwidth and central frequency of the femtosecond laser field. The theoretical results show that the change of the intermediate state detuning can effectively influence the enhancement of the near-resonant part, which further affects the transform-limited （TL）-normalized final state population maximum. Moreover, as the laser spectrum bandwidth increases, the TL-normalized final state population maximum can be effectively enhanced due to the increase of the enhancement in the near-resonant part, but the TL-normalized final state population maximum is constant by varying the laser central frequency. These studies can provide a clear physical picture for understanding the coherent features of the resonance-mediated two-photon absorption, and can also provide a theoretical guidance for the future applications.
基金Supported by the National High-Technology Research and Development Program of China under Grant No 2006AA03Z401, One-Hundred Talents Program of Chinese Academy of Sciences, and the National Natural Science Foundation of China under Grant No 60876033.
文摘We report the molecular beam epitaxy growth of 1.3 μm InAs/GaAs quantum-dot （QD） lasers with high characteristic temperature T0. The active region of the lasers consists of five-layer InAs QDs with p-type modulation doping. Devices with a stripe width of 4 μm and a cavity length of 1200 μm are fabricated and tested in the pulsed regime under different temperatures. It is found that T0 of the QD lasers is as high as 532 K in the temperature range from 10°C to 60°C. In addition, the aging test for the lasers under continuous wave operation at 100°C for 72 h shows almost no degradation, indicating the high crystal quality of the devices.
基金Deutsche Forschungsgemeinschaft (DFG), Germany (Grant number GR 1782/12)Science and Engineering Research Board (SERB), India (Grant number EMR/2015/001175)
文摘Laser induced periodic surface structures(LIPSS)represent a kind of top down approach to produce highly reproducible nano/microstructures without going for any sophisticated process of lithography.This method is much simpler and cost effective.In this work,LIPSS on Si surfaces were generated using femtosecond laser pulses of 800 nm wavelength.Photocatalytic substrates were prepared by depositing TiO2 thin films on top of the structured and unstructured Si wafer.The coatings were produced by sputtering from a Ti target in two different types of oxygen atmospheres.In first case,the oxygen pressure within the sputtering chamber was chosen to be high(3×10^–2 mbar)whereas it was one order of magnitude lower in second case(2.1×10^–3 mbar).In photocatalytic dye decomposition study of Methylene blue dye it was found that in the presence of LIPSS the activity can be enhanced by 2.1 and 3.3 times with high pressure and low pressure grown TiO2 thin films,respectively.The increase in photocatalytic activity is attributed to the enlargement of effective surface area.In comparative study,the dye decomposition rates of TiO2 thin films grown on LIPSS are found to be much higher than the value for standard reference thin film material Pilkington Activ^TM.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.21673211 and 21203047)the Foundation of Heilongjiang Bayi Agricultural University,China(Grant No.XZR2014-16)the Science Challenging Program of China(Grant No.JCKY2016212A501)
文摘The structural deformation of NO2 group induced by an intense femtosecond laser field of liquid nitromethane（NM）molecule is detected by time-and frequency-resolved coherent anti-Stokes Raman spectroscopy（CARS） technique with the intense pump laser. Here, we present the mechanism of molecular alignment and deformation. The CARS spectra and its FFT spectra of liquid NM show that the NO2 torsional mode couples with the CN symmetric stretching mode and that the NO2 group undergoes ultrafast structural deformation with a relaxation time of 195 fs. The frequency of the NO2 torsional mode in liquid NM（50.8±0.3 cm^-1） at room temperature is found. Our results prove the structural deformation of two groups in liquid NM molecule occur simultaneously in the intense laser field.
基金Item Sponsored by National Natural Science Foundation of China(51131002,51301196)Fundamental Research Funds for the Central Universities of China(YWF-15-CLXY-002)Fok Ying Tong Education Foundation of China(142008)
文摘The surface of Ni_（61）Nb_（39） crystalline ingot was treated by laser surface melting with different processing parameters.A fully amorphous layer with a thickness of approximately 10μm could be produced on the top surface under optimal parameters.An amorphous-crystalline composite layer with the depth from 10 to 50μm,consisting of amorphous matrix and intermetallic phases of Ni_3 Nb and Ni_6Nb_7,could be formed.The micro-hardness（about 831HV）of the treated surface was remarkably improved by nearly 100% compared with the value of the crystalline substrate caused by the formation of the fully amorphous structure.A finite volume simulation was adopted to evaluate the temperature distribution in the laser-affected zone of Ni_（61）Nb_（39） alloys and to reveal the mechanism of glass formation in the laser-affected zone.
基金Ministerio de Ciencia,Innovación y Universidades(PID2021-125483NB-I00,PGC2018-095595-B-I00)。
文摘Engineering ultrashort laser pulses is crucial for advancing fundamental research fields and applications.Controlling their spatiotemporal behavior,tailored to specific applications,can unlock new experimental capabilities.However,achieving this control is particularly challenging due to the difficulty in independently structuring their intensity and spatial phase distributions,given their polychromatic bandwidth.This article addresses this challenge by presenting a technique for generating flying structured laser pulses with tunable spatiotemporal behavior.We developed a comprehensive approach to directly design and govern these laser pulses.This method elucidates the role jointly played by the pulse's spatiotemporal couplings and its prescribed phase gradient in governing the pulse dynamics.It evidences that the often-overlooked design of the phase gradient is indeed essential for achieving programmable spatiotemporal control of the pulses.By tailoring the prescribed phase gradient,we demonstrate the creation of,to our knowledge,novel families of flying structured laser pulses that travel at the speed of light in helical spring and vortex multi-ring forms of different geometries.The achieved control over the dynamics of their intensity peaks and wavefronts is analyzed in detail.For instance,the intensity peak can be configured as a THz rotating light spot or shaped as a curve,enabling simultaneous substrate illumination at rates of tens of THz,far exceeding the MHz rates typically used in laser material processing.Additionally,the independent manipulation of the pulse wavefronts allows local tuning of the orbital angular momentum density carried by the beam.Together,these advancements unveil advantageous capabilities that have been sought after for many years,especially in ultrafast optics and light-matter interaction research.
基金supported by the French ANRT agence nationale de la recherche technologique under the CIFRE conventions industrielles de formation par la recherche framework.
文摘This review examines the state-of-the-art in spatial manipulation of ultrafast laser processing using dynamic light modulators,with a particular focus on liquid crystal-based systems.We discuss phase modulation strategies and highlight the current limitations and challenges in surface and bulk processing.Specifically,we emphasize the delicate balance between high-fidelity beam shaping and energy efficiency,both critical for surface and bulk processing applications.Given the inherent physical limitations of spatial light modulators such as spatial resolution,fill factor,and phase modulation range.We explore techniques developed to bridge the gap between desired intensity distributions and actual experimental beam profiles.We present various laser light modulation technologies and the main algorithmic strategies for obtaining modulation patterns.The paper includes application examples across a wide range of fields,from surgery to surface structuring,cutting,bulk photo-inscription of optical functions,and additive manufacturing,highlighting the significant enhancements in processing speed and precision due to spatial beam shaping.The diverse applications and the technological limitations underscore the need for adapted modulation pattern calculation methods.We discuss several advancements addressing these challenges,involving both experimental and algorithmic developments,including the recent incorporation of artificial intelligence.Additionally,we cover recent progress in phase and pulse front control based on spatial modulators,which introduces an extra control parameter for light excitation with high potential for achieving more controlled processing outcomes.
基金Supported by the National Natural Science Foundation of China under Grant No 60678043.
文摘The mathematical expression of the electron diffusion and drift length LDE of exponential doping photocathode is deduced. In the quantum efficiency equation of the reflection-mode uniform doping cathode, substituting LDE for LD, the equivalent quantum efficiency equation of the reflection-mode exponential doping cathode is obtained. By using the equivalent equation, theoretical simulation and experimental analysis shows that the equivalent index formula and formula-doped cathode quantum efficiency results in line. The equivalent equation avoids complicated calculation, thereby simplifies the process of solving the quantum efficiency of exponential doping photocathode.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10774001, 60736033, 60776041 and 60876041, and National Basic Research Program of China under Grant Nos 2006CB604908 and 2006CB921607, and the National Key Basic R＆D Plan of China under Grant Nos TG2007CB307004.
文摘We report on the growth and fabrication of deep ultraviolet （DUV） light emitting diodes （LEDs） on an AIN template which was grown on a pulsed atomic-layer epitaxial buffer layer. Threading dislocation densities in the AlN layer are greatly decreased with the introduction of this buffer layer. The crystalline quality of the AlGaN epilayer is further improved by using a low-temperature GaN interlayer between AlGaN and AlN. Electroluminescences of different DUV-LED devices at a wavelength of between 262 and 317nm are demonstrated. To improve the hole concentration of p-type AlGaN, Mg-doping with trimethylindium assistance approach is performed. It is found that the serial resistance of DUV-LED decreases and the performance of DUV-LED such as EL properties is improved.
基金Supported by the National Natural Science Foundation of China under Grant No 50902042, the Natural Science Foundation of Hebei Province under Grant No E2009000209, and the Education Office Foundation of Hebei Province under Grant No 2009313.
文摘Ce3＋/Eu2＋ codoped LiSrBO3 phosphor is synthesized, and its luminescent characteristics are investigated. LiSrBO3：Ce3＋,Eu2＋ phosphor exhibits varied hues from blue to white and eventually to yellow by resonance-type energy transfer from Ce3＋ ion to Eu2＋ ion and tuning the relative proportion of Ce3＋/Eu2＋ properly. Energy transfer mechanism in LiSrBOa：Ce3＋, Eu2＋ phosphor is dominated by the dipole-dipole interaction, and the critical distance of the energy transfer is estimated to be about 2 nm by both spectral overlap and concentration quenching methods. Under UV radiation, white light is generated by coupling 436 and 565nm emission bands attributed to Ce3＋ and Eu2＋ radiations, respectively.
基金Supported by the National High Technology Research and Development Program of China under Grant No 2007AA01Z258, the National Natural Science Foundation of China under Grant Nos 60807013 and 60837002.
文摘A type of multi-core Er-doped photosensitive silica optical fiber （MC-EDPF） is proposed and fabricated, in which a high consistency Er-doped core is surrounded by six high consistency Ge-doped cores. The multi-core design can overcome the difficulties encountered in the design and fabrication of single-core EDPFs through a modified chemical vapor deposition method combined with solution doping technology, and there is a conflict between high consistency Er doping and high consistency Ce doping. The absorption of MC-EDPFs achieved 15.876dB/m at 1550mm and lOdB/m at 98Ohm. The refleetivity of the fiber Bragg gratings （FBCs） written directly on the MC-EDPFs is as much as 96.84%.
文摘Silica microspheres self-assembled in glass capillary are investigated. Monodisperse silica microsphere dispersions in diameter 320nm are self-organized into a bulk cylindrical colloidal crystal by evaporation induced nucleation and crystallization. The resulting colloidal crystals are characterized by optical microscopy and scanning electronic microscopy （SEM）, and the SEM images show these crystals dominate in fcc lattice with its （111） crystallographic axis as longitudinal. The colloidal crystal filled capillary is packaged into a heat-shrink plastic tube and a fiber measurement system is designed to measure the optical property of colloidal bulk in capillary. It is found that an appreciable bandgap appears at wavelength 686 nm from the transmission spectroscopy, which is consistent with the theoretical estimation. A considerable photonic band gap of up to -10 dB and a steep photonic band edge of up to 0.25 dB/nm indicate that silica microspheres are promising for implementing optical filter applications in fiber systems.
