Femtosecond laser ablation(FLA)has been playing a prominent role in precision fabrication of material because of its circumvention of thermal effect and extremely high spatial resolution.Molecular dynamics modeling,as...Femtosecond laser ablation(FLA)has been playing a prominent role in precision fabrication of material because of its circumvention of thermal effect and extremely high spatial resolution.Molecular dynamics modeling,as a powerful tool to study the mechanism of femtosecond laser ablation,still lacks the connection between its simulation results and experimental observations at present.Here we combine a single-shot chirped spectral mapping ultrafast photography(CSMUP)technique in experiment and a three-dimensional two-temperature model-based molecular dynamics(3D TTM-MD)method in theory to jointly investigate the FLA process of bulky gold.Our experimental and simulated results show quite high consistency in time-resolved morphologic dynamics.According to the highly accurate simulations,the FLA process of gold at the high laser fluence is dominated by the phase explosion,which shows drastic vaporized cluster eruption and pressure dynamics,while the FLA process at the low laser fluence mainly results from the photomechanical spallation,which shows moderate temperature and pressure dynamics.This study reveals the ultrafast dynamics of gold with different ablation schemes,which has a guiding significance for the applications of FLA on various kinds of materials.展开更多
We design a set of processing devices to drill the shaped holes of turbine blades by using a femtosecond laser which outputs 1064 nm 5 W pulses at 100 kHz,investigate the mechanism of the femtosecond laser interaction...We design a set of processing devices to drill the shaped holes of turbine blades by using a femtosecond laser which outputs 1064 nm 5 W pulses at 100 kHz,investigate the mechanism of the femtosecond laser interaction with metals,and demonstrate that ultrafast laser drilling has distinct strong points against electric spark and longer laser pulse processing.The advantages related to no recast layer,no thermal effect,no micro crack,high precision,and high processing efficiency are carried out.展开更多
Femtosecond laser-induced surface structures upon multiple pulses irradiation are strongly correlated with the pulse number,which in turn signifcantly afects successive laser-material interactions.By recording the dyn...Femtosecond laser-induced surface structures upon multiple pulses irradiation are strongly correlated with the pulse number,which in turn signifcantly afects successive laser-material interactions.By recording the dynamics of femtosecond laser ablation of silicon using time-resolved shadowgraphy,here we present direct visualization of the excitation of air plasma induced by the refected laser during the second pulse irradiation.Te interaction of the air plasma and silicon plasma is found to enhance the shockwave expansion induced by silicon ablation in the longitudinal direction,showing anisotropic expansion dynamics in diferent directions.We further demonstrate the vanishing of air plasma as the pulse number increases because of the generation of a rough surface without light focusing ability.In the scenario,the interaction of air plasma and silicon plasma disappears;the expansion of the silicon plasma and shockwave restores its original characteristic that is dominated by the laser-material coupling.Te results show that the excitation of air plasma and the laser-material coupling involved in laser-induced plasma and shockwave expansion are structure mediated and dependent on the pulse number,which is of fundamental importance for deep insight into the nature of laser-material interactions during multiple pulses ablation.展开更多
The ultrashort pulse laser writing multi-layered data bits in fused silica for three-dimensional optical data storage through the mechanism of optical damage induced by multi-photon absorption is demonstrated.The 800 ...The ultrashort pulse laser writing multi-layered data bits in fused silica for three-dimensional optical data storage through the mechanism of optical damage induced by multi-photon absorption is demonstrated.The 800 nm,120 fs Ti:Sapphire laser beam is focused into cubic samples with a 0.65 NA commercial microscope objective.The size of the recorded bits can be smaller than 0.5 × 0.5 × 2.5μm as the laser pulse energy is lower than 300 nJ and the corresponding bit data storage density is 0.2 × 10^(12) Tbits/cm^(3).Due to the aberration produced by the mismatch of the refractive indices between the recording material and its immersion medium,the longitudinal size of the recorded bit increases and the contrast of the bit to surrounding uninfected zone decreases as the bit plane gets deeper.Hence a relatively lower storage density of 0.05 × 10^(12) Tbits/cm3 is realized.展开更多
All-dielectric metasurfaces offer low material loss and strong field localization and are,therefore,well suited for ultrathin and compact optical devices for electomagnetic wave manipulation at the nanoscale.All-silic...All-dielectric metasurfaces offer low material loss and strong field localization and are,therefore,well suited for ultrathin and compact optical devices for electomagnetic wave manipulation at the nanoscale.All-silicon dielectric metasurfaces,in particular,may additionally offer the desired compatibility with complementary metal-oxide semiconductor technology and,hence,are ideal candidates for large-scale monolithic integration on a photonic chip.However,in conventional silicon microfabrication approaches,the combination of mask photolithography with reactive ion etching usually involves expensive masks and multiple preprocessing stages leading to increased cost and fabrication times.In this work,a singlestep lithographical approach is proposed for the realization of all-silicon dielectric resonant metasurfaces that involves femtosecond laser processing of silicon below ablation threshold in combination with subsequent wet chemical etching.The method exploits the different etching rate between laser-modified and untreated regions,enabling large-area fabrication of patterned silicon surfaces in a facile and costefficient manufacturing approach.It is presented how two-dimensional silicon micro/nanostructures with controllable features,such as nanocones,can be effectively generated and,as a proof of concept,an allsilicon dielectric metasurface device supporting antiferromagnetic order is experimentally demonstrated.展开更多
Ethylene, the simplest model of a carbon-carbon double bond system, is pivotal in numerous chemical and biological processes. By employing intense infrared laser pump-probe techniques alongside coincidence measurement...Ethylene, the simplest model of a carbon-carbon double bond system, is pivotal in numerous chemical and biological processes. By employing intense infrared laser pump-probe techniques alongside coincidence measurements, we investigate the ultrafast non-adiabatic dynamics involved in the breakage of carbon-carbon double bonds and hydrogen elimination in dissociation of ethylene. Our study entails analyzing the dynamic kinetic energy release spectra to assess three bond-breaking scenarios, movements of nuclei, and structural changes around the carbon atoms. This allows us to evaluate the relaxation dynamics and characteristics of various dissociative states. Notably, we observe a significant rise in the yield of fragments resulting from C–H bond breakage with the delay time extended, suggesting non-adiabatic coupling through conical intersections from C–C bond breakage as a probable cause.展开更多
Generation of third-order harmonics at 800 nm of femtosecond laser pulses is studied in neutral atmospheric air and in plasma of optical breakdown in air.Its efficiency is measured at different fundamental laser inten...Generation of third-order harmonics at 800 nm of femtosecond laser pulses is studied in neutral atmospheric air and in plasma of optical breakdown in air.Its efficiency is measured at different fundamental laser intensities.A maximum efficiency is observed at the intensity when optical breakdown in atmospheric air starts.The factors that exhibit the main effects on the harmonic generation,including self-focusing in a neutral air and self-focusing in plasma,are discussed.展开更多
Single-shot 2-dimensional optical imaging of transient phenomena is indispensable for numerous areas of study.Among existing techniques,compressed ultrafast photography(CUP)using a chirped ultrashort pulse as active i...Single-shot 2-dimensional optical imaging of transient phenomena is indispensable for numerous areas of study.Among existing techniques,compressed ultrafast photography(CUP)using a chirped ultrashort pulse as active illumination can acquire nonrepetitive time-evolving events at hundreds of trillions of frames per second.However,the bulky size and conventional configurations limit its reliability and application scopes.Superdispersive metalenses offer a promising solution for an ultracompact design with a stable performance by integrating the functions of a focusing lens and dispersive optical components into a single device.Nevertheless,existing metalens designs,typically optimized for the full visible spectrum with a relatively low spectral resolution,cannot be readily applied to active-illumination CUP.To address these limitations,here,we propose single-shot compressed ultracompact femtophotography(CUF)that synergically combines the fields of nanophotonics,optical imaging,compressed sensing,and deep learning.We develop the theory of CUF’s data acquisition composed of temporal–spectral mapping,spatial encoding,temporal shearing,and spatiotemporal integration.We also develop CUF’s image reconstruction via deep learning.Moreover,we design and evaluate CUF’s crucial components—a static binary transmissive mask,a superdispersive metalens,and a 2-dimensional sensor.Finally,using numerical simulations,CUF’s feasibility is verified using 2 synthetic scenes:an ultrafast beam sweeping across a surface and the propagation of a terahertz Cherenkov wave.展开更多
Femtosecond pulses from an ultrafast mode-locked fiber laser can be optimized in real time by combining single-shot spectral measurements with a smart genetic algorithm to actively control and drive the intracavity dy...Femtosecond pulses from an ultrafast mode-locked fiber laser can be optimized in real time by combining single-shot spectral measurements with a smart genetic algorithm to actively control and drive the intracavity dynamics.展开更多
基金National Natural Science Foundation of China(91850202,92150301,12074121,62105101,62175066,11727810,12034008)Science and Technology Commission of Shanghai Municipality(21XD1400900,20ZR1417100,21JM0010700).
文摘Femtosecond laser ablation(FLA)has been playing a prominent role in precision fabrication of material because of its circumvention of thermal effect and extremely high spatial resolution.Molecular dynamics modeling,as a powerful tool to study the mechanism of femtosecond laser ablation,still lacks the connection between its simulation results and experimental observations at present.Here we combine a single-shot chirped spectral mapping ultrafast photography(CSMUP)technique in experiment and a three-dimensional two-temperature model-based molecular dynamics(3D TTM-MD)method in theory to jointly investigate the FLA process of bulky gold.Our experimental and simulated results show quite high consistency in time-resolved morphologic dynamics.According to the highly accurate simulations,the FLA process of gold at the high laser fluence is dominated by the phase explosion,which shows drastic vaporized cluster eruption and pressure dynamics,while the FLA process at the low laser fluence mainly results from the photomechanical spallation,which shows moderate temperature and pressure dynamics.This study reveals the ultrafast dynamics of gold with different ablation schemes,which has a guiding significance for the applications of FLA on various kinds of materials.
基金the National Special Fund of China for the Development of Major Research Equipment and Instruments under Grant No 2011YQ120075.
文摘We design a set of processing devices to drill the shaped holes of turbine blades by using a femtosecond laser which outputs 1064 nm 5 W pulses at 100 kHz,investigate the mechanism of the femtosecond laser interaction with metals,and demonstrate that ultrafast laser drilling has distinct strong points against electric spark and longer laser pulse processing.The advantages related to no recast layer,no thermal effect,no micro crack,high precision,and high processing efficiency are carried out.
基金Tis research was supported by the National Key R&D Program of China(grant no.2017YFB1104300)and the National Natural Science Foundation of China(grant nos.91323301,11704028).
文摘Femtosecond laser-induced surface structures upon multiple pulses irradiation are strongly correlated with the pulse number,which in turn signifcantly afects successive laser-material interactions.By recording the dynamics of femtosecond laser ablation of silicon using time-resolved shadowgraphy,here we present direct visualization of the excitation of air plasma induced by the refected laser during the second pulse irradiation.Te interaction of the air plasma and silicon plasma is found to enhance the shockwave expansion induced by silicon ablation in the longitudinal direction,showing anisotropic expansion dynamics in diferent directions.We further demonstrate the vanishing of air plasma as the pulse number increases because of the generation of a rough surface without light focusing ability.In the scenario,the interaction of air plasma and silicon plasma disappears;the expansion of the silicon plasma and shockwave restores its original characteristic that is dominated by the laser-material coupling.Te results show that the excitation of air plasma and the laser-material coupling involved in laser-induced plasma and shockwave expansion are structure mediated and dependent on the pulse number,which is of fundamental importance for deep insight into the nature of laser-material interactions during multiple pulses ablation.
基金Supported by National Kay Basic Research Special Foundation under Grant No.G1999075207National Natural Science Foundation of China under Grant Nos.19884001 and 19525412.
文摘The ultrashort pulse laser writing multi-layered data bits in fused silica for three-dimensional optical data storage through the mechanism of optical damage induced by multi-photon absorption is demonstrated.The 800 nm,120 fs Ti:Sapphire laser beam is focused into cubic samples with a 0.65 NA commercial microscope objective.The size of the recorded bits can be smaller than 0.5 × 0.5 × 2.5μm as the laser pulse energy is lower than 300 nJ and the corresponding bit data storage density is 0.2 × 10^(12) Tbits/cm^(3).Due to the aberration produced by the mismatch of the refractive indices between the recording material and its immersion medium,the longitudinal size of the recorded bit increases and the contrast of the bit to surrounding uninfected zone decreases as the bit plane gets deeper.Hence a relatively lower storage density of 0.05 × 10^(12) Tbits/cm3 is realized.
基金supported by the EU's H2020 framework program for research and innovation under the NFFA-Europe-Pilot project(Grant No.101007417).
文摘All-dielectric metasurfaces offer low material loss and strong field localization and are,therefore,well suited for ultrathin and compact optical devices for electomagnetic wave manipulation at the nanoscale.All-silicon dielectric metasurfaces,in particular,may additionally offer the desired compatibility with complementary metal-oxide semiconductor technology and,hence,are ideal candidates for large-scale monolithic integration on a photonic chip.However,in conventional silicon microfabrication approaches,the combination of mask photolithography with reactive ion etching usually involves expensive masks and multiple preprocessing stages leading to increased cost and fabrication times.In this work,a singlestep lithographical approach is proposed for the realization of all-silicon dielectric resonant metasurfaces that involves femtosecond laser processing of silicon below ablation threshold in combination with subsequent wet chemical etching.The method exploits the different etching rate between laser-modified and untreated regions,enabling large-area fabrication of patterned silicon surfaces in a facile and costefficient manufacturing approach.It is presented how two-dimensional silicon micro/nanostructures with controllable features,such as nanocones,can be effectively generated and,as a proof of concept,an allsilicon dielectric metasurface device supporting antiferromagnetic order is experimentally demonstrated.
基金supported by the National Natural Science Foundation of China (Grant Nos. 12134005, 92261201, and 12274179)。
文摘Ethylene, the simplest model of a carbon-carbon double bond system, is pivotal in numerous chemical and biological processes. By employing intense infrared laser pump-probe techniques alongside coincidence measurements, we investigate the ultrafast non-adiabatic dynamics involved in the breakage of carbon-carbon double bonds and hydrogen elimination in dissociation of ethylene. Our study entails analyzing the dynamic kinetic energy release spectra to assess three bond-breaking scenarios, movements of nuclei, and structural changes around the carbon atoms. This allows us to evaluate the relaxation dynamics and characteristics of various dissociative states. Notably, we observe a significant rise in the yield of fragments resulting from C–H bond breakage with the delay time extended, suggesting non-adiabatic coupling through conical intersections from C–C bond breakage as a probable cause.
基金Supported by National Key Basic Research Special Foundation under Grant No.G1999075207the National Natural Science Foundation of China under Grant Nos.19884001 and 19525412.
文摘Generation of third-order harmonics at 800 nm of femtosecond laser pulses is studied in neutral atmospheric air and in plasma of optical breakdown in air.Its efficiency is measured at different fundamental laser intensities.A maximum efficiency is observed at the intensity when optical breakdown in atmospheric air starts.The factors that exhibit the main effects on the harmonic generation,including self-focusing in a neutral air and self-focusing in plasma,are discussed.
基金supported in part by Natural Sciences and Engineering Research Council of Canada(RGPIN-2017-05959,RGPAS-2017-507845,I2IPJ-555593-20,RGPIN-2018-06217,RGPAS-2018-522650,and RGPIN-2019-06138)Canada Foundation for Innovation and Ministere de P'Economie et de P'Innovation du Quebec(37146)+1 种基金Fonds de Recherche du Quebec-Nature et Technologies(203345-Centre d'Optique,Photonique,et Lasers)Canada Research Chairs Program(CRC-2022-00119)。
文摘Single-shot 2-dimensional optical imaging of transient phenomena is indispensable for numerous areas of study.Among existing techniques,compressed ultrafast photography(CUP)using a chirped ultrashort pulse as active illumination can acquire nonrepetitive time-evolving events at hundreds of trillions of frames per second.However,the bulky size and conventional configurations limit its reliability and application scopes.Superdispersive metalenses offer a promising solution for an ultracompact design with a stable performance by integrating the functions of a focusing lens and dispersive optical components into a single device.Nevertheless,existing metalens designs,typically optimized for the full visible spectrum with a relatively low spectral resolution,cannot be readily applied to active-illumination CUP.To address these limitations,here,we propose single-shot compressed ultracompact femtophotography(CUF)that synergically combines the fields of nanophotonics,optical imaging,compressed sensing,and deep learning.We develop the theory of CUF’s data acquisition composed of temporal–spectral mapping,spatial encoding,temporal shearing,and spatiotemporal integration.We also develop CUF’s image reconstruction via deep learning.Moreover,we design and evaluate CUF’s crucial components—a static binary transmissive mask,a superdispersive metalens,and a 2-dimensional sensor.Finally,using numerical simulations,CUF’s feasibility is verified using 2 synthetic scenes:an ultrafast beam sweeping across a surface and the propagation of a terahertz Cherenkov wave.
文摘Femtosecond pulses from an ultrafast mode-locked fiber laser can be optimized in real time by combining single-shot spectral measurements with a smart genetic algorithm to actively control and drive the intracavity dynamics.
