Ultrafast phenomena induced by femtosecond laser irradiation encompass a range of highly dynamic physical processes,including but not limited to electron excitation,material ablation,plasma generation,and shock wave p...Ultrafast phenomena induced by femtosecond laser irradiation encompass a range of highly dynamic physical processes,including but not limited to electron excitation,material ablation,plasma generation,and shock wave propagation.Unveiling the dynamics of these ultrafast processes is crucial for effectively controlling laser processing.However,many of these phenomena occur on timescales ranging from femtoseconds(fs) to nanoseconds(ns),which presents significant challenges in monitoring and interpretation;thus,ultrafast optical imaging techniques are often required.This paper comprehensively reviews the ultrafast optical imaging methods employed in recent years to monitor various ultrafast processes such as electron excitation,ultrafast ablation,plasma ejection,and shock wave propagation during femtosecond laser processing of metallic,composite,and ceramic materials.These methods can be categorized into two primary types:pump-probe ultrafast optical imaging and single-shot ultrafast optical imaging techniques.The working principles and key findings associated with each type of ultrafast optical imaging technique are described in detail.Finally,the imaging principles,advantages and disadvantages,and application scenarios of various ultrafast imaging technologies are summarized,along with a discussion of future challenges and development directions in this field.展开更多
Ultrafast imaging is key for the real-time visualization of many transient events in physics,chemistry,and biology.The past decade has witnessed the blossom of new theories and technologies that have substantially pro...Ultrafast imaging is key for the real-time visualization of many transient events in physics,chemistry,and biology.The past decade has witnessed the blossom of new theories and technologies that have substantially propelled ultrafast imaging.The newly developed ultrafast imaging systems,in turn,have enabled unprecedented applications in both fundamental and applied sciences that unveil many new scientific discoveries ranging from carrier dynamics to brain functions.To date,ultrafast imaging marks an active frontier in both research and innovation.展开更多
Understanding laser induced ultrafast processes with complex three-dimensional(3D)geometries and extreme property evolution offers a unique opportunity to explore novel physical phenomena and to overcome the manufactu...Understanding laser induced ultrafast processes with complex three-dimensional(3D)geometries and extreme property evolution offers a unique opportunity to explore novel physical phenomena and to overcome the manufacturing limitations.Ultrafast imaging offers exceptional spatiotemporal resolution and thus has been considered an effective tool.However,in conventional single-view imaging techniques,3D information is projected on a two-dimensional plane,which leads to significant information loss that is detrimental to understanding the full ultrafast process.Here,we propose a quasi-3D imaging method to describe the ultrafast process and further analyze spatial asymmetries of laser induced plasma.Orthogonally polarized laser pulses are adopted to illuminate reflection-transmission views,and binarization techniques are employed to extract contours,forming the corresponding two-dimensional matrix.By rotating and multiplying the two-dimensional contour matrices obtained from the dual views,a quasi-3D image can be reconstructed.This successfully reveals dual-phase transition mechanisms and elucidates the diffraction phenomena occurring outside the plasma.Furthermore,the quasi-3D image confirms the spatial asymmetries of the picosecond plasma,which is difficult to achieve with two-dimensional images.Our findings demonstrate that quasi-3D imaging not only offers a more comprehensive understanding of plasma dynamics than previous imaging methods,but also has wide potential in revealing various complex ultrafast phenomena in related fields including strong-field physics,fluid dynamics,and cutting-edge manufacturing.展开更多
The ultrafast active cavitation imaging(UACI)based on plane wave transmission and delay-and-sum(DAS)beamforming has been developed to monitor cavitation events with a high frame rate.However,DAS beamforming leads to i...The ultrafast active cavitation imaging(UACI)based on plane wave transmission and delay-and-sum(DAS)beamforming has been developed to monitor cavitation events with a high frame rate.However,DAS beamforming leads to images with limited resolution and contrast.In this paper,minimum variance(M V)adaptive beamforming and coherence factor(CF)weighting are combined to achieve an MVCF-based UACI,which can improve the cavitation imaging quality.The detailed algorithm evaluation has been investigated from both simulation and experimental data The simulation data include10point targets and a cyst,while the experimental data are obtained by detecting the dissipation of cavitation bubbles in water excited by a single element transducer with frequency of1.2MHz.The advantages of the proposed methodology as well as the comparison with conventional B-mode,DAS?M V,DAS-CF and MV on the basis of compressive sensing(CS)(called MVCS)beamformers are discussed.The results show that MVCF beamformer has a significant improvement in terms of both resolutions and signal-to-noise ratio(SN R).The MVCF-based UACI has a SNR at21.82dB higher,lateral and axial resolution at2.69times and1.93times?respectively,which were compared with those of B-mode active cavitation mapping.The MVCF-based UACI can be used to image the residual cavitation bubbles with a higher SNR and better spatial resolution展开更多
We report direct nanoscale imaging of ultrafast plasmon in a gold dolmen nanostructure excited with the 7is laser pulses by combining the interferometric time-resolved technology with the three-photon photoemission el...We report direct nanoscale imaging of ultrafast plasmon in a gold dolmen nanostructure excited with the 7is laser pulses by combining the interferometric time-resolved technology with the three-photon photoemission electron microscopy （PEEM）. The interferometric time-resolved traces show that the plasmon mode beating pattern appears at the ends of the dimer slabs in the dolmen nanostructure as a result of coherent superposition of multiple localized surface plasmon modes induced by broad bandwidth of the ultrafast laser pulses. The PEEM measurement further discloses that in-phase of the oscillation field of two neighbor defects are surprisingly observed, which is attributed to the plasmon coupling between them. Furthermore, the control of the temporal delay between the pump and probe laser pluses could be utilized for manipulation of the near-field distribution. These findings deepen our understanding of ultrafast plasmon dynamics in a complex nanosystem.展开更多
BACKGROUND Severely elevated intracranial pressure due to various reasons,such as decreased cerebral perfusion,can lead to devastating neurological outcomes,such as brain herniation.Decompression craniectomy is a life...BACKGROUND Severely elevated intracranial pressure due to various reasons,such as decreased cerebral perfusion,can lead to devastating neurological outcomes,such as brain herniation.Decompression craniectomy is a life-saving procedure that is commonly performed for such a critical situation,but the changes in cerebral microvessels after brain herniation and decompression are unclear.Ultrafast power Doppler imaging(uPDI)is a new microvascular imaging technology that utilizes high frame rate plane/diverging wave transmission and advanced clutter filters.uPDI significantly improves Doppler sensitivity and can detect microvessels,which are usually invisible using traditional ultrasound Doppler imaging.CASE SUMMARY In this report,uPDI was used for the first time to observe the brain blood flow of a hypoperfusion area in a 4-year-old girl who underwent decompression craniectomy due to refractory intracranial hypertension(ICP)after malignant brain tumor surgery.B-mode imaging was used to verify the increased densities of the cerebral cortex and basal ganglia that were observed by computed tomography.CONCLUSION uPDI showed the local blood supplies and anatomical structures of the patient after decompressive craniectomy.uPDI is potentially a more intuitive and noninvasive method for evaluating the effects of severe ICP on cerebral microvessels.展开更多
Single-shot ultrafast compressed imaging(UCI)is an effective tool for studying ultrafast dynamics in physics,chemistry,or material science because of its excellent high frame rate and large frame number.However,the ra...Single-shot ultrafast compressed imaging(UCI)is an effective tool for studying ultrafast dynamics in physics,chemistry,or material science because of its excellent high frame rate and large frame number.However,the random code(Rcode)used in traditional UCI will lead to low-frequency noise covering high-frequency information due to its uneven sampling interval,which is a great challenge in the fidelity of large-frame reconstruction.Here,a high-frequency enhanced compressed active photography(H-CAP)is proposed.By uniformizing the sampling interval of R-code,H-CAP capture the ultrafast process with a random uniform sampling mode.This sampling mode makes the high-frequency sampling energy dominant,which greatly suppresses the low-frequency noise blurring caused by R-code and achieves high-frequency information of image enhanced.The superior dynamic performance and large-frame reconstruction ability of H-CAP are verified by imaging optical self-focusing effect and static object,respectively.We applied H-CAP to the spatial-temporal characterization of double-pulse induced silicon surface ablation dynamics,which is performed within 220 frames in a single-shot of 300 ps.H-CAP provides a high-fidelity imaging method for observing ultrafast unrepeatable dynamic processes with large frames.展开更多
Femtosecond laser technology has attracted significant attention from the viewpoints of fundamental and application;especially femtosecond laser processing materials present the unique mechanism of laser-material inte...Femtosecond laser technology has attracted significant attention from the viewpoints of fundamental and application;especially femtosecond laser processing materials present the unique mechanism of laser-material interaction.Under the extreme nonequilibrium conditions imposed by femtosecond laser irradiation,many fundamental questions concerning the physical origin of the material removal process remain unanswered.In this review,cutting-edge ultrafast dynamic observation techniques for investigating the fundamental questions,including timeresolved pump-probe shadowgraphy,ultrafast continuous optical imaging,and four-dimensional ultrafast scanning electron microscopy,are comprehensively surveyed.Each technique is described in depth,beginning with its basic principle,followed by a description of its representative applications in laser-material interaction and its strengths and limitations.The consideration of temporal and spatial resolutions and panoramic measurement at different scales are two major challenges.Hence,the prospects for technical advancement in this field are discussed finally.展开更多
How the state of living muscles modulates the features of nonlinear elastic waves generated by external dynamic loads remains unclear because of the challenge of directly observing and modeling nonlinear elastic waves...How the state of living muscles modulates the features of nonlinear elastic waves generated by external dynamic loads remains unclear because of the challenge of directly observing and modeling nonlinear elastic waves in skeletal muscles in vivo,considering their active deformation behavior.Here,this important issue is addressed by combining experiments performed with an ultrafast ultrasound imaging system to track nonlinear shear waves(shear shock waves)in muscles in vivo and finite element analysis relying on a physically motivated constitutive model to study the effect of muscle activation level.Skeletal muscle was loaded with a deep muscle stimulator to generate shear shock waves(SSWs).The particle velocities,second and third harmonics,and group velocities of the SSWs in living muscles under both passive and active states were measured in vivo.Our experimental results reveal,for the first time,that muscle states have a pronounced effect on wave features;a low level of activation may facilitate the occurrence of both the second and third harmonics,whereas a high level of activation may inhibit the third harmonic.Finite element analysis was further carried out to quantitatively explore the effect of active muscle deformation behavior on the generation and propagation of SSWs.The simulation results at different muscle activation levels confirmed the experimental findings.The ability to reveal the effects of muscle state on the features of SSWs may be helpful in elucidating the unique dynamic deformation mechanism of living skeletal muscles,quantitatively characterizing diverse shock wave-based therapy instruments,and guiding the design of muscle-mimicking soft materials.展开更多
We report a framing imaging based on noncollinear optical parametric amplification(NCOPA),named FINCOPA,which applies NCOPA for the first time to single-shot ultrafast optical imaging.In an experiment targeting a lase...We report a framing imaging based on noncollinear optical parametric amplification(NCOPA),named FINCOPA,which applies NCOPA for the first time to single-shot ultrafast optical imaging.In an experiment targeting a laser-induced air plasma grating,FINCOPA achieved 50 fs-resolved optical imaging with a spatial resolution of^83 lp∕mm and an effective frame rate of 10 trillion frames per second(Tfps).It has also successfully visualized an ultrafast rotating optical field with an effective frame rate of 15 Tfps.FINCOPA has simultaneously a femtosecond-level temporal resolution and frame interval and a micrometer-level spatial resolution.Combining outstanding spatial and temporal resolutions with an ultrahigh frame rate,FINCOPA will contribute to high-spatiotemporal resolution observations of ultrafast transient events,such as atomic or molecular dynamics in photonic materials,plasma physics,and laser inertial-confinement fusion.展开更多
Spatiotemporal shaping of ultrashort pulses is pivotal for various technologies,such as burst laser ablation and ultrafast imaging.However,the difficulty of pulse stretching to subnanosecond intervals and independent ...Spatiotemporal shaping of ultrashort pulses is pivotal for various technologies,such as burst laser ablation and ultrafast imaging.However,the difficulty of pulse stretching to subnanosecond intervals and independent control of the spatial profile for each pulse limit their advancement.We present a pulse manipulation technique for producing spectrally separated GHz burst pulses from a single ultrashort pulse,where each pulse is spatially shapable.We demonstrated the production of pulse trains at intervals of 0.1 to 3 ns in the 800-and 400-nm wavelength bands and applied them to ultrafast single-shot transmission spectroscopic imaging(4 Gfps)of laser ablation dynamics with two-color sequentially timed all-optical mapping photography.Furthermore,we demonstrated the production of pulse trains containing a shifted or dual-peak pulse as examples of individual spatial shaping of GHz burst pulses.Our proposed technique brings unprecedented spatiotemporal manipulation of GHz burst pulses,which can be useful for a wide range of laser applications.展开更多
Single-shot ultrafast multidimensional optical imaging(UMOI)combines ultrahigh temporal resolution with multidimensional imaging capabilities in a snapshot,making it an essential tool for real-time detection and analy...Single-shot ultrafast multidimensional optical imaging(UMOI)combines ultrahigh temporal resolution with multidimensional imaging capabilities in a snapshot,making it an essential tool for real-time detection and analysis of ultrafast scenes.However,current single-shot UMOI techniques cannot simultaneously capture the spatial-temporal-spectral complex amplitude information,hampering it from complete analyses of ultrafast scenes.To address this issue,we propose a single-shot spatial-temporal-spectral complex amplitude imaging(STS-CAI)technique using wavelength and time multiplexing.By employing precise modulation of a broadband pulse via an encoding plate in coherent diffraction imaging and spatial-temporal shearing through a wide-open-slit streak camera,dual-mode multiplexing image reconstruction of wavelength and time is achieved,which significantly enhances the efficiency of information acquisition.Experimentally,a custom-built STS-CAI apparatus precisely measures the spatiotemporal characteristics of picosecond spatiotemporally chirped and spatial vortex pulses,respectively.STS-CAI demonstrates both ultrahigh temporal resolution and robust phase sensitivity.Prospectively,this technique is valuable for spatiotemporal coupling measurements of large-aperture ultrashort pulses and offers promising applications in both fundamental research and applied sciences.展开更多
Dynamic phenomena occurring on the ultrafast time scales are inherently difficult to image.While pump–probe techniques have been used for decades,probing nonrepeatable phenomena precludes this form of imaging.Additio...Dynamic phenomena occurring on the ultrafast time scales are inherently difficult to image.While pump–probe techniques have been used for decades,probing nonrepeatable phenomena precludes this form of imaging.Additionally,many ultrafast phenomena,such as electron dynamics,exhibit low amplitude contrast in the optical wavelength range and thus require quantitative phase imaging.To better understand the underlying physics involved in a plethora of ultrafast phenomena,advanced imaging techniques must be developed to observe single events at an ultrafast time scale.Here,we present,to the best of our knowledge,the first ptychographic imaging system capable of observing ultrafast dynamics from a single event.We demonstrate ultrafast dynamic imaging by observing the conduction band electron population from a 2-photon absorption event in ZnSe pumped by a single femtosecond pulse.We verify experimental observations by comparing them to numeric solutions of a nonlinear envelope equation.Our imaging method represents a major step forward in ultrafast imaging,bringing the capabilities of ptychography to the ultrafast regime.展开更多
A tunable ultrafast intensity-rotating optical field is generated by overlapping a pair of 20Hz,800 nm chirped pulses with a Michelson interferometer(MI).Its rotating rate can be up to 10 trillion radians per second(T...A tunable ultrafast intensity-rotating optical field is generated by overlapping a pair of 20Hz,800 nm chirped pulses with a Michelson interferometer(MI).Its rotating rate can be up to 10 trillion radians per second(Trad/s),which can be flexibly tuned with a mirror in the MI.Besides,its fold rotational symmetry structure is also changeable by controlling the difference from the topological charges of the pulse pair.Experimentally,we have successfully developed a twopetal lattice with a tunable rotating speed from 3.9 Trad/s up to 11.9 Trad/s,which is confirmed by our single-shot ultrafast frame imager based on noncollinear optical-parametric amplification with its highest frame rate of 15 trillion frames per second(Tfps).This work is carried out at a low repetition rate.Therefore,it can be applied at relativistic,even ultrarelativistic,intensities,which usually operate in low repetition rate ultrashort and ultraintense laser systems.We believe that it may have application in laser-plasma-based accelerators,strong terahertz radiations and celestial phenomena.展开更多
To reveal the fundamental aspects hidden behind a variety of transient events in mechanics,physics,and biology,the highly desired ability to acquire three-dimensional(3D)images with ultrafast temporal resolution has b...To reveal the fundamental aspects hidden behind a variety of transient events in mechanics,physics,and biology,the highly desired ability to acquire three-dimensional(3D)images with ultrafast temporal resolution has been long sought.As one of the most commonly employed 3D sensing techniques,fringe projection profilometry(FPP)reconstructs the depth of a scene from stereo images taken with sequentially structured illuminations.However,the imaging speed of current FPP methods is generally capped at several kHz,which is limited by the projector-camera hardware and the number of fringe patterns required for phase retrieval and unwrapping.Here we report a novel learning-based ultrafast 3D imaging technique,termed single-shot super-resolved FPP(SSSR-FPP),which enables ultrafast 3D imaging at 100,000 Hz.SSSR-FPP uses only one pair of low signal-to-noise ratio(SNR),low-resolution,and pixelated fringe patterns as input,while the high-resolution unwrapped phase and fringe orders can be deciphered with a specific trained deep neural network.Our approach exploits the significant speed gain achieved by reducing the imaging window of conventional high-speed cameras,while"regenerating"the lost spatial resolution through deep learning.To demonstrate the high spatio-temporal resolution of SSSR-FPP,we present 3D videography of several transient scenes,including rotating turbofan blades,exploding building blocks,and the reciprocating motion of a steam engine,etc.,which were previously challenging or even impossible to capture with conventional methods.Experimental results establish SSSR-FPP as a significant step forward in the field of 3D optical sensing,offering new insights into a broad spectrum of dynamic processes across various scientific disciplines.展开更多
Transient imaging has recently made a huge impact in the computer graphics and computer vision fields.By capturing,reconstructing,or simulating light transport at extreme temporal resolutions,researchers have proposed...Transient imaging has recently made a huge impact in the computer graphics and computer vision fields.By capturing,reconstructing,or simulating light transport at extreme temporal resolutions,researchers have proposed novel techniques to show movies of light in motion,see around corners,detect objects in highly-scattering media,or infer material properties from a distance,to name a few.The key idea is to leverage the wealth of information in the temporal domain at the pico or nanosecond resolution,infor-mation usually lost during the capture-time temporal integration.This paper presents recent advances in this field of transient imaging from a graphics and vision perspective,including capture techniques,analysis,applications and simulation.展开更多
Compressed ultrafast photography(CUP)is a burgeoning single-shot computational imaging technique that provides an imaging speed as high as 10 trillion frames per second and a sequence depth of up to a few hundred fram...Compressed ultrafast photography(CUP)is a burgeoning single-shot computational imaging technique that provides an imaging speed as high as 10 trillion frames per second and a sequence depth of up to a few hundred frames.This technique synergizes compressed sensing and the streak camera technique to capture nonrepeatable ultrafast transient events with a single shot.With recent unprecedented technical developments and extensions of this methodology,it has been widely used in ultrafast optical imaging and metrology,ultrafast electron diffraction and microscopy,and information security protection.We review the basic principles of CUP,its recent advances in data acquisition and image reconstruction,its fusions with other modalities,and its unique applications in multiple research fields.展开更多
In ultrafast optical imaging,it is critical to obtain the spatial structure,temporal evolution,and spectral composition of the object with snapshots in order to better observe and understand unrepeatable or irreversib...In ultrafast optical imaging,it is critical to obtain the spatial structure,temporal evolution,and spectral composition of the object with snapshots in order to better observe and understand unrepeatable or irreversible dynamic scenes.However,so far,there are no ultrafast optical imaging techniques that can simultaneously capture the spatial–temporal–spectral five-dimensional(5D)information of dynamic scenes.To break the limitation of the existing techniques in imaging dimensions,we develop a spectral-volumetric compressed ultrafast photography(SV-CUP)technique.In our SV-CUP,the spatial resolutions in the x,y and z directions are,respectively,0.39,0.35,and 3 mm with an 8.8 mm×6.3 mm field of view,the temporal frame interval is 2 ps,and the spectral frame interval is 1.72 nm.To demonstrate the excellent performance of our SV-CUP in spatial–temporal–spectral 5D imaging,we successfully measure the spectrally resolved photoluminescent dynamics of a 3D mannequin coated with CdSe quantum dots.Our SV-CUP brings unprecedented detection capabilities to dynamic scenes,which has important application prospects in fundamental research and applied science.展开更多
Microscale charge and energy transfer is an ultrafast process that can determine the photoelectrochemical performance of devices.However,nonlinear and nonequilibrium properties hinder our understanding of ultrafast pr...Microscale charge and energy transfer is an ultrafast process that can determine the photoelectrochemical performance of devices.However,nonlinear and nonequilibrium properties hinder our understanding of ultrafast processes;thus,the direct imaging strategy has become an effective means to uncover ultrafast charge and energy transfer processes.Due to diffraction limits of optical imaging,the obtained optical image has insufficient spatial resolution.Therefore,electron beam imaging combined with a pulse laser showing high spatial–temporal resolution has become a popular area of research,and numerous breakthroughs have been achieved in recent years.In this review,we cover three typical ultrafast electron beam imaging techniques,namely,time-resolved photoemission electron microscopy,scanning ultrafast electron microscopy,and ultrafast transmission electron microscopy,in addition to the principles and characteristics of these three techniques.Some outstanding results related to photon–electron interactions,charge carrier transport and relaxation,electron–lattice coupling,and lattice oscillation are also reviewed.In summary,ultrafast electron beam imaging with high spatial–temporal resolution and multidimensional imaging abilities can promote the fundamental under-standing of physics,chemistry,and optics,as well as guide the development of advanced semiconductors and electronics.展开更多
In this Letter,a coding aperture design framework is introduced for data sampling of a CUP-VISAR system in laser inertial confinement fusion(ICF)research.It enhances shock wave velocity fringe reconstruction through f...In this Letter,a coding aperture design framework is introduced for data sampling of a CUP-VISAR system in laser inertial confinement fusion(ICF)research.It enhances shock wave velocity fringe reconstruction through feature fusion with a convolutional variational auto-encoder(CVAE)network.Simulation and experimental results indicate that,compared to random coding aperture,the proposed coding matrices exhibit superior reconstruction quality,achieving more accurate fringe pattern reconstruction and resolving coding information aliasing.In the experiments,the system signal-to-noise ratio(SNR)and reconstruction quality can be improved by increasing the light transmittance of the encoding matrix.This framework aids in diagnosing ICF in challenging experimental settings.展开更多
基金supported by the National Key R&D Program of China(No.2022YFB4601601)the Key R&D Program of Guangxi Province,China(No.GKAB23026101)+1 种基金the Base,Talent Special Project of the Guangxi Science and Technology Plan Project(No.Gui Ke AD23026149)Guangxi Natural Science Foundation,China(No.2023GXNSFBA026287)
文摘Ultrafast phenomena induced by femtosecond laser irradiation encompass a range of highly dynamic physical processes,including but not limited to electron excitation,material ablation,plasma generation,and shock wave propagation.Unveiling the dynamics of these ultrafast processes is crucial for effectively controlling laser processing.However,many of these phenomena occur on timescales ranging from femtoseconds(fs) to nanoseconds(ns),which presents significant challenges in monitoring and interpretation;thus,ultrafast optical imaging techniques are often required.This paper comprehensively reviews the ultrafast optical imaging methods employed in recent years to monitor various ultrafast processes such as electron excitation,ultrafast ablation,plasma ejection,and shock wave propagation during femtosecond laser processing of metallic,composite,and ceramic materials.These methods can be categorized into two primary types:pump-probe ultrafast optical imaging and single-shot ultrafast optical imaging techniques.The working principles and key findings associated with each type of ultrafast optical imaging technique are described in detail.Finally,the imaging principles,advantages and disadvantages,and application scenarios of various ultrafast imaging technologies are summarized,along with a discussion of future challenges and development directions in this field.
文摘Ultrafast imaging is key for the real-time visualization of many transient events in physics,chemistry,and biology.The past decade has witnessed the blossom of new theories and technologies that have substantially propelled ultrafast imaging.The newly developed ultrafast imaging systems,in turn,have enabled unprecedented applications in both fundamental and applied sciences that unveil many new scientific discoveries ranging from carrier dynamics to brain functions.To date,ultrafast imaging marks an active frontier in both research and innovation.
文摘Understanding laser induced ultrafast processes with complex three-dimensional(3D)geometries and extreme property evolution offers a unique opportunity to explore novel physical phenomena and to overcome the manufacturing limitations.Ultrafast imaging offers exceptional spatiotemporal resolution and thus has been considered an effective tool.However,in conventional single-view imaging techniques,3D information is projected on a two-dimensional plane,which leads to significant information loss that is detrimental to understanding the full ultrafast process.Here,we propose a quasi-3D imaging method to describe the ultrafast process and further analyze spatial asymmetries of laser induced plasma.Orthogonally polarized laser pulses are adopted to illuminate reflection-transmission views,and binarization techniques are employed to extract contours,forming the corresponding two-dimensional matrix.By rotating and multiplying the two-dimensional contour matrices obtained from the dual views,a quasi-3D image can be reconstructed.This successfully reveals dual-phase transition mechanisms and elucidates the diffraction phenomena occurring outside the plasma.Furthermore,the quasi-3D image confirms the spatial asymmetries of the picosecond plasma,which is difficult to achieve with two-dimensional images.Our findings demonstrate that quasi-3D imaging not only offers a more comprehensive understanding of plasma dynamics than previous imaging methods,but also has wide potential in revealing various complex ultrafast phenomena in related fields including strong-field physics,fluid dynamics,and cutting-edge manufacturing.
基金National Natural Science Foundation of China(No.11604305)Key Research and Development Projects from Ministry of Science and Technology of the People’s Republic of China(No.2016YFC0101605)
文摘The ultrafast active cavitation imaging(UACI)based on plane wave transmission and delay-and-sum(DAS)beamforming has been developed to monitor cavitation events with a high frame rate.However,DAS beamforming leads to images with limited resolution and contrast.In this paper,minimum variance(M V)adaptive beamforming and coherence factor(CF)weighting are combined to achieve an MVCF-based UACI,which can improve the cavitation imaging quality.The detailed algorithm evaluation has been investigated from both simulation and experimental data The simulation data include10point targets and a cyst,while the experimental data are obtained by detecting the dissipation of cavitation bubbles in water excited by a single element transducer with frequency of1.2MHz.The advantages of the proposed methodology as well as the comparison with conventional B-mode,DAS?M V,DAS-CF and MV on the basis of compressive sensing(CS)(called MVCS)beamformers are discussed.The results show that MVCF beamformer has a significant improvement in terms of both resolutions and signal-to-noise ratio(SN R).The MVCF-based UACI has a SNR at21.82dB higher,lateral and axial resolution at2.69times and1.93times?respectively,which were compared with those of B-mode active cavitation mapping.The MVCF-based UACI can be used to image the residual cavitation bubbles with a higher SNR and better spatial resolution
基金Supported by the National Basic Research Program of China under Grant No 2013CB922404the National Natural Science Foundation of China under Grant Nos 11474040,11474039,61605017 and 61575030the Project of Changchun Science and Technology Bureau under Grant No 14KP007
文摘We report direct nanoscale imaging of ultrafast plasmon in a gold dolmen nanostructure excited with the 7is laser pulses by combining the interferometric time-resolved technology with the three-photon photoemission electron microscopy （PEEM）. The interferometric time-resolved traces show that the plasmon mode beating pattern appears at the ends of the dimer slabs in the dolmen nanostructure as a result of coherent superposition of multiple localized surface plasmon modes induced by broad bandwidth of the ultrafast laser pulses. The PEEM measurement further discloses that in-phase of the oscillation field of two neighbor defects are surprisingly observed, which is attributed to the plasmon coupling between them. Furthermore, the control of the temporal delay between the pump and probe laser pluses could be utilized for manipulation of the near-field distribution. These findings deepen our understanding of ultrafast plasmon dynamics in a complex nanosystem.
文摘BACKGROUND Severely elevated intracranial pressure due to various reasons,such as decreased cerebral perfusion,can lead to devastating neurological outcomes,such as brain herniation.Decompression craniectomy is a life-saving procedure that is commonly performed for such a critical situation,but the changes in cerebral microvessels after brain herniation and decompression are unclear.Ultrafast power Doppler imaging(uPDI)is a new microvascular imaging technology that utilizes high frame rate plane/diverging wave transmission and advanced clutter filters.uPDI significantly improves Doppler sensitivity and can detect microvessels,which are usually invisible using traditional ultrasound Doppler imaging.CASE SUMMARY In this report,uPDI was used for the first time to observe the brain blood flow of a hypoperfusion area in a 4-year-old girl who underwent decompression craniectomy due to refractory intracranial hypertension(ICP)after malignant brain tumor surgery.B-mode imaging was used to verify the increased densities of the cerebral cortex and basal ganglia that were observed by computed tomography.CONCLUSION uPDI showed the local blood supplies and anatomical structures of the patient after decompressive craniectomy.uPDI is potentially a more intuitive and noninvasive method for evaluating the effects of severe ICP on cerebral microvessels.
基金supported by the National Science Foundation of China(No.12127806,No.62175195 and No.12304382)the International Joint Research Laboratory for Micro/Nano Manufacturing and Measurement Technologies.
文摘Single-shot ultrafast compressed imaging(UCI)is an effective tool for studying ultrafast dynamics in physics,chemistry,or material science because of its excellent high frame rate and large frame number.However,the random code(Rcode)used in traditional UCI will lead to low-frequency noise covering high-frequency information due to its uneven sampling interval,which is a great challenge in the fidelity of large-frame reconstruction.Here,a high-frequency enhanced compressed active photography(H-CAP)is proposed.By uniformizing the sampling interval of R-code,H-CAP capture the ultrafast process with a random uniform sampling mode.This sampling mode makes the high-frequency sampling energy dominant,which greatly suppresses the low-frequency noise blurring caused by R-code and achieves high-frequency information of image enhanced.The superior dynamic performance and large-frame reconstruction ability of H-CAP are verified by imaging optical self-focusing effect and static object,respectively.We applied H-CAP to the spatial-temporal characterization of double-pulse induced silicon surface ablation dynamics,which is performed within 220 frames in a single-shot of 300 ps.H-CAP provides a high-fidelity imaging method for observing ultrafast unrepeatable dynamic processes with large frames.
基金supported by the National Natural Science Foundation of China under Grant Nos.51975054,61605140 and 11704028the National Key R&D Program of China(2017YFB1104300)。
文摘Femtosecond laser technology has attracted significant attention from the viewpoints of fundamental and application;especially femtosecond laser processing materials present the unique mechanism of laser-material interaction.Under the extreme nonequilibrium conditions imposed by femtosecond laser irradiation,many fundamental questions concerning the physical origin of the material removal process remain unanswered.In this review,cutting-edge ultrafast dynamic observation techniques for investigating the fundamental questions,including timeresolved pump-probe shadowgraphy,ultrafast continuous optical imaging,and four-dimensional ultrafast scanning electron microscopy,are comprehensively surveyed.Each technique is described in depth,beginning with its basic principle,followed by a description of its representative applications in laser-material interaction and its strengths and limitations.The consideration of temporal and spatial resolutions and panoramic measurement at different scales are two major challenges.Hence,the prospects for technical advancement in this field are discussed finally.
基金supported by the National Students Training Program for Innovation(Grant No.202210007029)。
文摘How the state of living muscles modulates the features of nonlinear elastic waves generated by external dynamic loads remains unclear because of the challenge of directly observing and modeling nonlinear elastic waves in skeletal muscles in vivo,considering their active deformation behavior.Here,this important issue is addressed by combining experiments performed with an ultrafast ultrasound imaging system to track nonlinear shear waves(shear shock waves)in muscles in vivo and finite element analysis relying on a physically motivated constitutive model to study the effect of muscle activation level.Skeletal muscle was loaded with a deep muscle stimulator to generate shear shock waves(SSWs).The particle velocities,second and third harmonics,and group velocities of the SSWs in living muscles under both passive and active states were measured in vivo.Our experimental results reveal,for the first time,that muscle states have a pronounced effect on wave features;a low level of activation may facilitate the occurrence of both the second and third harmonics,whereas a high level of activation may inhibit the third harmonic.Finite element analysis was further carried out to quantitatively explore the effect of active muscle deformation behavior on the generation and propagation of SSWs.The simulation results at different muscle activation levels confirmed the experimental findings.The ability to reveal the effects of muscle state on the features of SSWs may be helpful in elucidating the unique dynamic deformation mechanism of living skeletal muscles,quantitatively characterizing diverse shock wave-based therapy instruments,and guiding the design of muscle-mimicking soft materials.
基金supported partly by the National Natural Science Foundation of China(Nos.61775142 and 61705132)the Shenzhen Basic Research Project on the subject layout(No.JCYJ20170412105812811)+1 种基金the Shenzhen Basic Research Projects(Nos.JCYJ20170412105812811,JCYJ20190808164007485,and JCYJ20190808115601653)the Natural Sciences and Engineering Research Council of Canada(Nos.RGPIN-2017-05959 and RGPAS-507845-2017)
文摘We report a framing imaging based on noncollinear optical parametric amplification(NCOPA),named FINCOPA,which applies NCOPA for the first time to single-shot ultrafast optical imaging.In an experiment targeting a laser-induced air plasma grating,FINCOPA achieved 50 fs-resolved optical imaging with a spatial resolution of^83 lp∕mm and an effective frame rate of 10 trillion frames per second(Tfps).It has also successfully visualized an ultrafast rotating optical field with an effective frame rate of 15 Tfps.FINCOPA has simultaneously a femtosecond-level temporal resolution and frame interval and a micrometer-level spatial resolution.Combining outstanding spatial and temporal resolutions with an ultrahigh frame rate,FINCOPA will contribute to high-spatiotemporal resolution observations of ultrafast transient events,such as atomic or molecular dynamics in photonic materials,plasma physics,and laser inertial-confinement fusion.
基金supported by MEXT Quantum Leap Flagship Program (MEXT Q-LEAP) (Grant No.JPMXS0118067246)K.S.was supported by JST ACT-X (JPMJAX22K8).Y.I.and A.I.were partly supported by JST PRESTO (JPMJPR2003 and JPMJPR1902,respectively)K.N.was partly supported by JST FOREST (JPMJFR215C).
文摘Spatiotemporal shaping of ultrashort pulses is pivotal for various technologies,such as burst laser ablation and ultrafast imaging.However,the difficulty of pulse stretching to subnanosecond intervals and independent control of the spatial profile for each pulse limit their advancement.We present a pulse manipulation technique for producing spectrally separated GHz burst pulses from a single ultrashort pulse,where each pulse is spatially shapable.We demonstrated the production of pulse trains at intervals of 0.1 to 3 ns in the 800-and 400-nm wavelength bands and applied them to ultrafast single-shot transmission spectroscopic imaging(4 Gfps)of laser ablation dynamics with two-color sequentially timed all-optical mapping photography.Furthermore,we demonstrated the production of pulse trains containing a shifted or dual-peak pulse as examples of individual spatial shaping of GHz burst pulses.Our proposed technique brings unprecedented spatiotemporal manipulation of GHz burst pulses,which can be useful for a wide range of laser applications.
基金supported by the National Natural Science Foundation of China(Grant Nos.12074121,12274139,and 12325408)the China Postdoctoral Science Foundation(Grant Nos.2023M743252 and 2024T170846)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.YZY24014)the Key Research and Development Program of Zhejiang Province(Grant No.2024SSYS0014).
文摘Single-shot ultrafast multidimensional optical imaging(UMOI)combines ultrahigh temporal resolution with multidimensional imaging capabilities in a snapshot,making it an essential tool for real-time detection and analysis of ultrafast scenes.However,current single-shot UMOI techniques cannot simultaneously capture the spatial-temporal-spectral complex amplitude information,hampering it from complete analyses of ultrafast scenes.To address this issue,we propose a single-shot spatial-temporal-spectral complex amplitude imaging(STS-CAI)technique using wavelength and time multiplexing.By employing precise modulation of a broadband pulse via an encoding plate in coherent diffraction imaging and spatial-temporal shearing through a wide-open-slit streak camera,dual-mode multiplexing image reconstruction of wavelength and time is achieved,which significantly enhances the efficiency of information acquisition.Experimentally,a custom-built STS-CAI apparatus precisely measures the spatiotemporal characteristics of picosecond spatiotemporally chirped and spatial vortex pulses,respectively.STS-CAI demonstrates both ultrahigh temporal resolution and robust phase sensitivity.Prospectively,this technique is valuable for spatiotemporal coupling measurements of large-aperture ultrashort pulses and offers promising applications in both fundamental research and applied sciences.
基金funded through the Air Force Office of Scientific Research(FA9550-22-1-0495)the Los Alamos National Laboratory。
文摘Dynamic phenomena occurring on the ultrafast time scales are inherently difficult to image.While pump–probe techniques have been used for decades,probing nonrepeatable phenomena precludes this form of imaging.Additionally,many ultrafast phenomena,such as electron dynamics,exhibit low amplitude contrast in the optical wavelength range and thus require quantitative phase imaging.To better understand the underlying physics involved in a plethora of ultrafast phenomena,advanced imaging techniques must be developed to observe single events at an ultrafast time scale.Here,we present,to the best of our knowledge,the first ptychographic imaging system capable of observing ultrafast dynamics from a single event.We demonstrate ultrafast dynamic imaging by observing the conduction band electron population from a 2-photon absorption event in ZnSe pumped by a single femtosecond pulse.We verify experimental observations by comparing them to numeric solutions of a nonlinear envelope equation.Our imaging method represents a major step forward in ultrafast imaging,bringing the capabilities of ptychography to the ultrafast regime.
基金supported by the National Natural Science Foundation of China(Nos.61775142,61705132,61490710 and 61827815)China Postdoctoral Science Foundation(No.2017M612726)+1 种基金Shenzhen Basic Research Project on Subject Layout(No.JCYJ20170412105812811)Fund of the International Collaborative Laboratory of 2D Materials for Optoelectronics Science and Technology,Shenzhen University(No.2DMOST2018019)。
文摘A tunable ultrafast intensity-rotating optical field is generated by overlapping a pair of 20Hz,800 nm chirped pulses with a Michelson interferometer(MI).Its rotating rate can be up to 10 trillion radians per second(Trad/s),which can be flexibly tuned with a mirror in the MI.Besides,its fold rotational symmetry structure is also changeable by controlling the difference from the topological charges of the pulse pair.Experimentally,we have successfully developed a twopetal lattice with a tunable rotating speed from 3.9 Trad/s up to 11.9 Trad/s,which is confirmed by our single-shot ultrafast frame imager based on noncollinear optical-parametric amplification with its highest frame rate of 15 trillion frames per second(Tfps).This work is carried out at a low repetition rate.Therefore,it can be applied at relativistic,even ultrarelativistic,intensities,which usually operate in low repetition rate ultrashort and ultraintense laser systems.We believe that it may have application in laser-plasma-based accelerators,strong terahertz radiations and celestial phenomena.
基金supported by National Key Research and Development Program of China(2022YFB2804603,2022YFA1205002,2024YFE0101300)National Natural Science Foundation of China(U21B2033,62075096,62105151,62175109,62227818,62361136588)+4 种基金Leading Technology of Jiangsu Basic Research Plan(BK20192003)"333 Engineering"Research Project of Jiangsu Province(BRA2016407)Jiangsu Provincial"One belt and one road"innovation cooperation project(BZ2020007)Fundamental Research Funds for the Central Universities(30921011208,30919011222,30920032101)Open Research Fund of Jiangsu Key Laboratory of Spectral Imaging&Intelligent Sense(USGP202105,JSGP202201).
文摘To reveal the fundamental aspects hidden behind a variety of transient events in mechanics,physics,and biology,the highly desired ability to acquire three-dimensional(3D)images with ultrafast temporal resolution has been long sought.As one of the most commonly employed 3D sensing techniques,fringe projection profilometry(FPP)reconstructs the depth of a scene from stereo images taken with sequentially structured illuminations.However,the imaging speed of current FPP methods is generally capped at several kHz,which is limited by the projector-camera hardware and the number of fringe patterns required for phase retrieval and unwrapping.Here we report a novel learning-based ultrafast 3D imaging technique,termed single-shot super-resolved FPP(SSSR-FPP),which enables ultrafast 3D imaging at 100,000 Hz.SSSR-FPP uses only one pair of low signal-to-noise ratio(SNR),low-resolution,and pixelated fringe patterns as input,while the high-resolution unwrapped phase and fringe orders can be deciphered with a specific trained deep neural network.Our approach exploits the significant speed gain achieved by reducing the imaging window of conventional high-speed cameras,while"regenerating"the lost spatial resolution through deep learning.To demonstrate the high spatio-temporal resolution of SSSR-FPP,we present 3D videography of several transient scenes,including rotating turbofan blades,exploding building blocks,and the reciprocating motion of a steam engine,etc.,which were previously challenging or even impossible to capture with conventional methods.Experimental results establish SSSR-FPP as a significant step forward in the field of 3D optical sensing,offering new insights into a broad spectrum of dynamic processes across various scientific disciplines.
基金This research has been partially funded by DARPA(project REVEAL),the European Re-search Council(Consolidator Grant,project CHAMELEON),and the Spanish Ministerio de Economía y Competitividad projects TIN2016-78753-P,TIN2016-79710-P and TIN2014-61696-EXPJulio Marco was additionally funded by a grant from the Gobierno de Aragón.
文摘Transient imaging has recently made a huge impact in the computer graphics and computer vision fields.By capturing,reconstructing,or simulating light transport at extreme temporal resolutions,researchers have proposed novel techniques to show movies of light in motion,see around corners,detect objects in highly-scattering media,or infer material properties from a distance,to name a few.The key idea is to leverage the wealth of information in the temporal domain at the pico or nanosecond resolution,infor-mation usually lost during the capture-time temporal integration.This paper presents recent advances in this field of transient imaging from a graphics and vision perspective,including capture techniques,analysis,applications and simulation.
基金This work was partially supported by the National Natural Science Foundation of China(Grant Nos.91850202,11774094,11727810,11804097,and 61720106009)the Science and Technology Commission of Shanghai Municipality(Grant Nos.19560710300 and 17ZR146900)the China Postdoctoral Science Foundation(Grant No.2018M641958).
文摘Compressed ultrafast photography(CUP)is a burgeoning single-shot computational imaging technique that provides an imaging speed as high as 10 trillion frames per second and a sequence depth of up to a few hundred frames.This technique synergizes compressed sensing and the streak camera technique to capture nonrepeatable ultrafast transient events with a single shot.With recent unprecedented technical developments and extensions of this methodology,it has been widely used in ultrafast optical imaging and metrology,ultrafast electron diffraction and microscopy,and information security protection.We review the basic principles of CUP,its recent advances in data acquisition and image reconstruction,its fusions with other modalities,and its unique applications in multiple research fields.
基金partially partially supported by the National Natural Science Foundation of China(Grant Nos.91850202,11774094,12074121,11804097,11727810,and 12034008)the Science and Technology Commission of Shanghai Municipality(Grant Nos.19560710300 and 20ZR1417100)Ministère des Relations internationales et de la Francophonie du Québec。
文摘In ultrafast optical imaging,it is critical to obtain the spatial structure,temporal evolution,and spectral composition of the object with snapshots in order to better observe and understand unrepeatable or irreversible dynamic scenes.However,so far,there are no ultrafast optical imaging techniques that can simultaneously capture the spatial–temporal–spectral five-dimensional(5D)information of dynamic scenes.To break the limitation of the existing techniques in imaging dimensions,we develop a spectral-volumetric compressed ultrafast photography(SV-CUP)technique.In our SV-CUP,the spatial resolutions in the x,y and z directions are,respectively,0.39,0.35,and 3 mm with an 8.8 mm×6.3 mm field of view,the temporal frame interval is 2 ps,and the spectral frame interval is 1.72 nm.To demonstrate the excellent performance of our SV-CUP in spatial–temporal–spectral 5D imaging,we successfully measure the spectrally resolved photoluminescent dynamics of a 3D mannequin coated with CdSe quantum dots.Our SV-CUP brings unprecedented detection capabilities to dynamic scenes,which has important application prospects in fundamental research and applied science.
文摘Microscale charge and energy transfer is an ultrafast process that can determine the photoelectrochemical performance of devices.However,nonlinear and nonequilibrium properties hinder our understanding of ultrafast processes;thus,the direct imaging strategy has become an effective means to uncover ultrafast charge and energy transfer processes.Due to diffraction limits of optical imaging,the obtained optical image has insufficient spatial resolution.Therefore,electron beam imaging combined with a pulse laser showing high spatial–temporal resolution has become a popular area of research,and numerous breakthroughs have been achieved in recent years.In this review,we cover three typical ultrafast electron beam imaging techniques,namely,time-resolved photoemission electron microscopy,scanning ultrafast electron microscopy,and ultrafast transmission electron microscopy,in addition to the principles and characteristics of these three techniques.Some outstanding results related to photon–electron interactions,charge carrier transport and relaxation,electron–lattice coupling,and lattice oscillation are also reviewed.In summary,ultrafast electron beam imaging with high spatial–temporal resolution and multidimensional imaging abilities can promote the fundamental under-standing of physics,chemistry,and optics,as well as guide the development of advanced semiconductors and electronics.
基金supported by the National Natural Science Foundation of China(Nos.12127810 and 61604028)the Science and Technology Research Program of Chongqing Municipal Education Commission(No.KJZD-K202200607)。
文摘In this Letter,a coding aperture design framework is introduced for data sampling of a CUP-VISAR system in laser inertial confinement fusion(ICF)research.It enhances shock wave velocity fringe reconstruction through feature fusion with a convolutional variational auto-encoder(CVAE)network.Simulation and experimental results indicate that,compared to random coding aperture,the proposed coding matrices exhibit superior reconstruction quality,achieving more accurate fringe pattern reconstruction and resolving coding information aliasing.In the experiments,the system signal-to-noise ratio(SNR)and reconstruction quality can be improved by increasing the light transmittance of the encoding matrix.This framework aids in diagnosing ICF in challenging experimental settings.
