Journals > > Topics > Special Issue for the 60th Anniversary of XIOPM of CAS, and the 50th Anniversary of the Acta Photonica Sinica Ⅱ
Special Issue for the 60th Anniversary of XIOPM of CAS, and the 50th Anniversary of the Acta Photonica Sinica Ⅱ|15 Article(s)
Electron Correlation Momentum and Energy Spectrum in Triple Ionization of Lithium by the Femtosecond Laser Field（Invited）
Shiwei LIU, Difa YE, and Jie LIU
The interaction between atoms and intense laser fields plays an important role in the field of ultrafast physics, which has become a powerful experimental technique to explore the structure and dynamics of matter. One of the critical issues is to explore the mechanism of laser-driven electron re-scattering process in, e.g., above-threshold ionization, high-order harmonic generation, and Non-Sequential Double/Multiple Ionization (NSDI/NSMI). Among them, the NSDI/NSMI is particularly interesting since it is a prototypical example for studying the electron-electron (e-e) correlation. During the past years, the general picture of NSDI has been established. In comparison, the NSMI is less well-understood although a series of experimental data have been collected, for example, extremely highly charged ions up to Ar16+, Kr19+, and Xe26+ have been produced in super-strong laser fields. Here, the involvement of the multi-shell multi-electron, as well as highly nonlinear relativistic and non-dipole effects, makes the electron dynamics much more complicated. As a result, the theoretical explanation is hindered and lagged far behind partially due to the fact that solving the full-dimensional Time-Dependent Schrödinger Equation (TDSE) is currently limited to two-electron systems, leaving the dynamics of NSMI highly unexplored. On the other aspect, the Classical Trajectory Monte Carlo (CTMC) approach has been widely applied to atomic and molecular collisions and ionization of atoms by strong laser fields, which can be readily implemented in many-body systems and provide intuitive pictures to the dynamical processes of interest. It should be noted that, however, a classical multi-electron atom with Coulomb interactions is typically unstable and might suffer nonphysical auto-ionization, which needs feasible 'quantum' modifications. this article investigates the laser-driven lithium triple ionization by the classical trajectory Monte Carlo with the Heisenberg potential (CTMC-H) model. The model introduces the Heisenberg potential to mimic the Heisenberg uncertainty principle, which can be applied to obtain the classical stable configuration of the ground state of lithium atom by minimizing the system Hamiltonian to the values of the ionization energies. By solving the classical canonical equations of electrons, we study the total ionization rate of Li in a wide range of laser intensities. Due to the unique shell structure of the alkali metal elements, the out-most electron of the lithium atom is loosely bound and can be easily ionized, while the inner shell electrons are deeply bound and difficult to be deprived because of the much larger ionization energy. Therefore, we find that the single ionization is saturated over a wide span of laser intensities, and the double and triple ionization can be triggered by the re-collision of the out-most electron, showing the typical knee structure around 30 and 60 PW/cm2, respectively. The difference between sequential triple ionization and non-sequential triple ionization is described in detail by plotting the momentum distribution of Li3+ in the polarization direction of the laser electric field, which shows a single peak structure near zero for the STI process and a double-hump structure in the NSTI regime as another signature of re-collision. Meanwhile, the magnetic effect is revealed by comparing the momentum spectra of Li3+ along the magnetic field polarization direction and the laser beam propagation direction. According to the energy distribution of three electrons mapped into the Dalitz diagram, we identify three types of re-collision mechanisms for the non-sequential triple ionization and reveal the fingerprint of thermalization induced by the (e, 3e) scattering mechanism. Besides, the electron re-scattering process is significant even in the sequential triple ionization region, e.g., at 100 PW/cm2, as evidenced by the high-energy electrons located at the corners of the Dalitz plot. These findings not only provide deep insight into the mechanisms of the multiple ionization of alkali metal atoms in a femtosecond strong laser field but also have potential applications in manipulating the electron correlation on the attosecond time scale. Finally, we would like to emphasize that recently the magneto-optical trap recoil ion momentum spectroscopy has been proposed and established by combining cold atom trapping technology, strong laser pulse, and ultra-fast technology, exhibiting the ability to measure the full-dimensional momentum spectra of multiple reaction products and thus extending the study of strong-field multiple ionization and ultra-fast processes to the alkali metal atoms. We hope our theoretical predictions might stimulate experiments in this direction. The interaction between atoms and intense laser fields plays an important role in the field of ultrafast physics, which has become a powerful experimental technique to explore the structure and dynamics of matter. One of the critical issues is to explore the mechanism of laser-driven electron re-scattering process in, e.g., above-threshold ionization, high-order harmonic generation, and Non-Sequential Double/Multiple Ionization (NSDI/NSMI). Among them, the NSDI/NSMI is particularly interesting since it is a prototypical example for studying the electron-electron (e-e) correlation. During the past years, the general picture of NSDI has been established. In comparison, the NSMI is less well-understood although a series of experimental data have been collected, for example, extremely highly charged ions up to Ar16+, Kr19+, and Xe26+ have been produced in super-strong laser fields. Here, the involvement of the multi-shell multi-electron, as well as highly nonlinear relativistic and non-dipole effects, makes the electron dynamics much more complicated. As a result, the theoretical explanation is hindered and lagged far behind partially due to the fact that solving the full-dimensional Time-Dependent Schrödinger Equation (TDSE) is currently limited to two-electron systems, leaving the dynamics of NSMI highly unexplored. On the other aspect, the Classical Trajectory Monte Carlo (CTMC) approach has been widely applied to atomic and molecular collisions and ionization of atoms by strong laser fields, which can be readily implemented in many-body systems and provide intuitive pictures to the dynamical processes of interest. It should be noted that, however, a classical multi-electron atom with Coulomb interactions is typically unstable and might suffer nonphysical auto-ionization, which needs feasible 'quantum' modifications. this article investigates the laser-driven lithium triple ionization by the classical trajectory Monte Carlo with the Heisenberg potential (CTMC-H) model. The model introduces the Heisenberg potential to mimic the Heisenberg uncertainty principle, which can be applied to obtain the classical stable configuration of the ground state of lithium atom by minimizing the system Hamiltonian to the values of the ionization energies. By solving the classical canonical equations of electrons, we study the total ionization rate of Li in a wide range of laser intensities. Due to the unique shell structure of the alkali metal elements, the out-most electron of the lithium atom is loosely bound and can be easily ionized, while the inner shell electrons are deeply bound and difficult to be deprived because of the much larger ionization energy. Therefore, we find that the single ionization is saturated over a wide span of laser intensities, and the double and triple ionization can be triggered by the re-collision of the out-most electron, showing the typical knee structure around 30 and 60 PW/cm2, respectively. The difference between sequential triple ionization and non-sequential triple ionization is described in detail by plotting the momentum distribution of Li3+ in the polarization direction of the laser electric field, which shows a single peak structure near zero for the STI process and a double-hump structure in the NSTI regime as another signature of re-collision. Meanwhile, the magnetic effect is revealed by comparing the momentum spectra of Li3+ along the magnetic field polarization direction and the laser beam propagation direction. According to the energy distribution of three electrons mapped into the Dalitz diagram, we identify three types of re-collision mechanisms for the non-sequential triple ionization and reveal the fingerprint of thermalization induced by the (e, 3e) scattering mechanism. Besides, the electron re-scattering process is significant even in the sequential triple ionization region, e.g., at 100 PW/cm2, as evidenced by the high-energy electrons located at the corners of the Dalitz plot. These findings not only provide deep insight into the mechanisms of the multiple ionization of alkali metal atoms in a femtosecond strong laser field but also have potential applications in manipulating the electron correlation on the attosecond time scale. Finally, we would like to emphasize that recently the magneto-optical trap recoil ion momentum spectroscopy has been proposed and established by combining cold atom trapping technology, strong laser pulse, and ultra-fast technology, exhibiting the ability to measure the full-dimensional momentum spectra of multiple reaction products and thus extending the study of strong-field multiple ionization and ultra-fast processes to the alkali metal atoms. We hope our theoretical predictions might stimulate experiments in this direction.
Acta Photonica Sinica
- Publication Date: Aug. 25, 2022
- Vol. 51, Issue 8, 0851519 (2022)
Intelligent Ultrafast Photonics Based on Machine Learning：Review and Prospect（Invited）
Jiajun PENG, Xiaohui LI, Sunfan XI, and Keqin JIAO
The convergence of machine learning and ultrafast photonics cutting-edge crossover technologies in the context of artificial intelligence takes an unconventional approach to provide an unparalleled photonic perspective. This intersection of computer science, photonics, and materials platforms will enable new approaches to the large-scale photonic design of unique functions as well as optical characterization, laying the cornerstone for efficient energy conversion systems. We envision that a global optimization framework based on a multi-step machine learning strategy can build a more general intelligent ultrafast photonic system, where the first step can be to define the main target function of the device and determine the appropriate photonic concept to provide the best performance. The second step is to select a suitable material platform and build an extensive database of optical materials. By using the selected material properties, an optimized design solution for the material device can be provided. The third step is to determine the appropriate fabrication conditions (growth conditions, doping levels, stoichiometry, etc.) and integration schemes. The interplay between new photonic structures and machine learning may overcome the limitations of current computational methods and systems, provide unparalleled capabilities in light-matter interactions and unlock new device concepts, and may lead ultrafast photonics research to new frontiers that could usher in a brighter era of artificial intelligence. The convergence of machine learning and ultrafast photonics cutting-edge crossover technologies in the context of artificial intelligence takes an unconventional approach to provide an unparalleled photonic perspective. This intersection of computer science, photonics, and materials platforms will enable new approaches to the large-scale photonic design of unique functions as well as optical characterization, laying the cornerstone for efficient energy conversion systems. We envision that a global optimization framework based on a multi-step machine learning strategy can build a more general intelligent ultrafast photonic system, where the first step can be to define the main target function of the device and determine the appropriate photonic concept to provide the best performance. The second step is to select a suitable material platform and build an extensive database of optical materials. By using the selected material properties, an optimized design solution for the material device can be provided. The third step is to determine the appropriate fabrication conditions (growth conditions, doping levels, stoichiometry, etc.) and integration schemes. The interplay between new photonic structures and machine learning may overcome the limitations of current computational methods and systems, provide unparalleled capabilities in light-matter interactions and unlock new device concepts, and may lead ultrafast photonics research to new frontiers that could usher in a brighter era of artificial intelligence.
Acta Photonica Sinica
- Publication Date: Aug. 25, 2022
- Vol. 51, Issue 8, 0851518 (2022)
Advances in Multicolor Single-molecule Localization Microscopy（Invited）
Yuehan ZHAO, and Xiang HAO
Finally, we present an outlook on the fast-growing field of multicolor single-molecule localization microscopy. One of the future development directions of multicolor single molecules is the research on probes, including the brighter organic fluorescent dyes or fluorescent proteins and more universal imaging buffers. Further research can also be done on reducing the complexity of the optical system and expanding the field of view of imaging. It can be envisioned that multicolor SMLM will play a more prominent role in biological and medical research for many years to come. We hope that this review can help researchers choose the appropriate multicolor SMLM for their own experiments. Finally, we present an outlook on the fast-growing field of multicolor single-molecule localization microscopy. One of the future development directions of multicolor single molecules is the research on probes, including the brighter organic fluorescent dyes or fluorescent proteins and more universal imaging buffers. Further research can also be done on reducing the complexity of the optical system and expanding the field of view of imaging. It can be envisioned that multicolor SMLM will play a more prominent role in biological and medical research for many years to come. We hope that this review can help researchers choose the appropriate multicolor SMLM for their own experiments.
Acta Photonica Sinica
- Publication Date: Aug. 25, 2022
- Vol. 51, Issue 8, 0851517 (2022)
Doppler Asymmetric Spatial Heterodyne Interferometry for Wind Measurement in Middle and Upper Atmosphere（Invited）
Yang XIAO, Yutao FENG, Zhenqing WEN, and Di FU
Atmospheric wind field is an important parameter to understand the dynamics and thermodynamic characteristics of the Earth's atmospheric system, and it is the basic data for weather forecasting, space environment monitoring, and climatology research. Passive optical remote sensing based on Optical interferometer is the main technical means of wind field measurement in the middle and upper atmosphere. In the 1960s, foreign research institutions began to use optical interferometers to detect upper atmospheric wind fields. and carried out the experimental research on interferometer payload technology simultaneously, and successively developed a series of representative scientific instruments and satellite payloads based on the Fabry-Pérot interferometer and the Wide Angle Michelson interferometer. In 2006, the ENGLERT C R research team of the U.S. Naval Research Laboratory proposed a new planetary atmospheric wind detection technology, called Doppler Asymmetric Spatial Heterodyne wind measurement technology, this technology detects the Doppler frequency shift of the atmospheric airglow spectrum by inverting the phase of the interferogram, thereby realizing the detection of the atmospheric wind field. Compared with the Fabry-Perot interferometer and the Wide-Angle Michelson interferometer, the Doppler Asymmetric Spatial Heterodyne interferometer has the following advantages: 1)Two-beam equivalent thickness spatial modulation interference, which relaxes the requirements for the optical index of the element; 2) Interferometer does not need Step-by-step scanning; 3) Wind speed inversion is based on the Fourier transform relationship between interferogram and spectrogram, so it does not need extremely narrow bandwidth (<1 nm) filters to separate single-line spectra; 4)Synchronous calibration can be achieved, the standard spectral line of the calibration light source and the target spectral line of the detection source are simultaneously introduced into the interferometer system to monitor the state change of the interferometer in real time, therefore, the measurement accuracy can be further improved. After nearly two decades, a series of research results have been achieved in basic theory, interferometer design, instrument development technology, data processing and wind speed retrieval of Doppler Asymmetric Spatial Heterodyne Interferometer. In terms of theoretical research progress, domestic and foreign scholars have theoretically analyzed the factors that affect the accuracy of interferometer phase inversion; In order to expand the detection capability of the Doppler Asymmetric Spatial Heterodyne Interferometer, four structural design schemes are proposed by referring to the spectral expansion method of the wide-spectru Spatial Heterodyne Spectroscopy; A series of interferogram preprocessing methods are proposed to eliminate the errors of the original interferogram caused by various defects of optical components, photoelectric sensors and optical systems. Foreign scholars put forward a wind field profile inversion method named “peeling onions”. In terms of instrument research progress, since the Doppler Asymmetric Spatial Heterodyne Interferometer wind measurement technology was proposed in 2006, many international research institutions have carried out research on the development process of the core components of the interferometer, and successfully developed a variety of interferometer prototypes covering from visible light to long-wave infrared ,such as Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI), Stratospheric Wind Interferometer for Transport studies- Doppler Asymmetric Spatial Heterodyne (SWIFT-DASH), and Redline DASH Demonstration Instrument (REDDI). Ground-based instruments and space-based payloads have also been developed to the stage of application and promotion. The main domestic research institute is the Xi'an Institute of Optics and Precision Mechanics of CAS, the institute focuses on the study of the interferometer thermal compensation method, the interferometer glass component design method, the interferometer component gluing and integration process, the interferometer support structure component design and integration process, and proposed a dual-band Doppler Asymmetric Spatial Heterodyne interferometer technology and a high-time-resolution ground-based Doppler Asymmetric Spatial Heterodyne interferometer technology, and developed a single-channel DASH principle prototype with oxygen atom 630 nm and oxygen molecule 867 nm airglow radiation as the target source.This paper reviews the domestic and foreign research progress of Doppler Asymmetric Spatial Heterodyne technology for atmospheric wind field detection, discusses its technical characteristics and application potential, and provides reference for the future development of atmospheric wind field passive optical remote sensing detection technology and mission planning in the field of atmospheric wind field detection in our country. Atmospheric wind field is an important parameter to understand the dynamics and thermodynamic characteristics of the Earth's atmospheric system, and it is the basic data for weather forecasting, space environment monitoring, and climatology research. Passive optical remote sensing based on Optical interferometer is the main technical means of wind field measurement in the middle and upper atmosphere. In the 1960s, foreign research institutions began to use optical interferometers to detect upper atmospheric wind fields. and carried out the experimental research on interferometer payload technology simultaneously, and successively developed a series of representative scientific instruments and satellite payloads based on the Fabry-Pérot interferometer and the Wide Angle Michelson interferometer. In 2006, the ENGLERT C R research team of the U.S. Naval Research Laboratory proposed a new planetary atmospheric wind detection technology, called Doppler Asymmetric Spatial Heterodyne wind measurement technology, this technology detects the Doppler frequency shift of the atmospheric airglow spectrum by inverting the phase of the interferogram, thereby realizing the detection of the atmospheric wind field. Compared with the Fabry-Perot interferometer and the Wide-Angle Michelson interferometer, the Doppler Asymmetric Spatial Heterodyne interferometer has the following advantages: 1)Two-beam equivalent thickness spatial modulation interference, which relaxes the requirements for the optical index of the element; 2) Interferometer does not need Step-by-step scanning; 3) Wind speed inversion is based on the Fourier transform relationship between interferogram and spectrogram, so it does not need extremely narrow bandwidth (<1 nm) filters to separate single-line spectra; 4)Synchronous calibration can be achieved, the standard spectral line of the calibration light source and the target spectral line of the detection source are simultaneously introduced into the interferometer system to monitor the state change of the interferometer in real time, therefore, the measurement accuracy can be further improved. After nearly two decades, a series of research results have been achieved in basic theory, interferometer design, instrument development technology, data processing and wind speed retrieval of Doppler Asymmetric Spatial Heterodyne Interferometer. In terms of theoretical research progress, domestic and foreign scholars have theoretically analyzed the factors that affect the accuracy of interferometer phase inversion; In order to expand the detection capability of the Doppler Asymmetric Spatial Heterodyne Interferometer, four structural design schemes are proposed by referring to the spectral expansion method of the wide-spectru Spatial Heterodyne Spectroscopy; A series of interferogram preprocessing methods are proposed to eliminate the errors of the original interferogram caused by various defects of optical components, photoelectric sensors and optical systems. Foreign scholars put forward a wind field profile inversion method named “peeling onions”. In terms of instrument research progress, since the Doppler Asymmetric Spatial Heterodyne Interferometer wind measurement technology was proposed in 2006, many international research institutions have carried out research on the development process of the core components of the interferometer, and successfully developed a variety of interferometer prototypes covering from visible light to long-wave infrared ,such as Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI), Stratospheric Wind Interferometer for Transport studies- Doppler Asymmetric Spatial Heterodyne (SWIFT-DASH), and Redline DASH Demonstration Instrument (REDDI). Ground-based instruments and space-based payloads have also been developed to the stage of application and promotion. The main domestic research institute is the Xi'an Institute of Optics and Precision Mechanics of CAS, the institute focuses on the study of the interferometer thermal compensation method, the interferometer glass component design method, the interferometer component gluing and integration process, the interferometer support structure component design and integration process, and proposed a dual-band Doppler Asymmetric Spatial Heterodyne interferometer technology and a high-time-resolution ground-based Doppler Asymmetric Spatial Heterodyne interferometer technology, and developed a single-channel DASH principle prototype with oxygen atom 630 nm and oxygen molecule 867 nm airglow radiation as the target source.This paper reviews the domestic and foreign research progress of Doppler Asymmetric Spatial Heterodyne technology for atmospheric wind field detection, discusses its technical characteristics and application potential, and provides reference for the future development of atmospheric wind field passive optical remote sensing detection technology and mission planning in the field of atmospheric wind field detection in our country.
Acta Photonica Sinica
- Publication Date: Aug. 25, 2022
- Vol. 51, Issue 8, 0851516 (2022)
High Harmonic Generation from Solids：the Phenomena，Mechanisms and Applications（Invited）
Tong WU, Chen QIAN, Zishao WANG, Xiangyu ZHANG, Chao YU, and Ruifeng LU
Light-matter interactions can be mainly described by transitions of electrons, accompanied by emission, absorption, or scattering of photons. Light absorption and emission of atoms, molecules, solids and other substances play a vital role in the development of science and technology.Because of its excellent monochromaticity, directivity and coherence, laser has become a powerful tool to detect the structure and properties of matter.With the development of laser technology, the peak power of the laser pulse reaches the order of 1015 W and the laser pulse durations decrease to a few femtoseconds. Advanced optical technology makes it possible to carry out experiments at an unprecedented intensity. When the electric field intensity of laser pulse reaches or even exceeds the electric field intensity of the Coulomb potential inside the substances, the concept that the laser field is regarded as a perturbation to the motion of electrons under the constraints of the Coulomb field is no longer applicable, accompanied by a series of highly nonlinear complex dynamic processes, such as multi-photon and above threshold ionization, tunneling ionization,nonsequential double ionization and High Harmonic Generation (HHG). In this context, the emergence of ultrashort and ultra-intense pulses gradually opened up the research of strong field physics. When a macroscopic system is exposed to intense laser fields whose forces are comparable to the binding forces of valence electrons, the system will emit coherent radiation with frequencies many times that of the driving laser field. This non-perturbativeand extremely nonlinear optical phenomenon is calledhigh-order harmonic generation, whichhas become a research direction of great concern in the field of strong field physicsas a Potential Extreme Ultraviolet (EUV) source and a possible means of real-time detection of ultrafast dynamics inside matter. In the past 30 years, HHG from gases has been developed greatly based on the physical image of the three-step model, which has laid a solid foundation for attosecond physics. HHG from solids provides a new way to miniaturize devices as a EUV light source and explore the electronic structure of condensed matter system. Meanwhile, in order to find more integrated and compact EUV light source, people gradually turn their attention to solid target.Experimental observation of non-perturbative transmitted high-order harmonics generated from ZnO crystal suggested that the solid-state HHG process can be illustrated neither by conventional perturbative nonlinear optics nor by the kinematics of strong-field re-scattering.More researches demonstrated that solid-state HHG can be achieved through a wide variety of interaction media with suitable laser wavelengths from the near-infrared to terahertz range.High harmonic generation from solid materials driven by an ultrafast strong laser is a fast developing direction in interdisciplinary fields of condensed matter physics, materials science, optics and photonics. So far, the target of solid-state HHG study has been expanded from bulk metals, semiconductors, insulators to low-dimensional nanostructures. Moreover, nonperturbative harmonic signals have been successfully detected in topological insulators and from topological surface states. Compared to gaseous atoms and molecules, solid materials have higher atomic density, and the mechanism of solid-state HHG is more complicated, thus solid-state HHG possesses good application prospects in achieving new light sources, exploring physical properties as well as characterizing microscopic dynamics of materials. This article mainly reviews the experimental and theoretical progresses of solid-state HHG in recent years, and also summarizes its mechanisms and potential applications. Light-matter interactions can be mainly described by transitions of electrons, accompanied by emission, absorption, or scattering of photons. Light absorption and emission of atoms, molecules, solids and other substances play a vital role in the development of science and technology.Because of its excellent monochromaticity, directivity and coherence, laser has become a powerful tool to detect the structure and properties of matter.With the development of laser technology, the peak power of the laser pulse reaches the order of 1015 W and the laser pulse durations decrease to a few femtoseconds. Advanced optical technology makes it possible to carry out experiments at an unprecedented intensity. When the electric field intensity of laser pulse reaches or even exceeds the electric field intensity of the Coulomb potential inside the substances, the concept that the laser field is regarded as a perturbation to the motion of electrons under the constraints of the Coulomb field is no longer applicable, accompanied by a series of highly nonlinear complex dynamic processes, such as multi-photon and above threshold ionization, tunneling ionization,nonsequential double ionization and High Harmonic Generation (HHG). In this context, the emergence of ultrashort and ultra-intense pulses gradually opened up the research of strong field physics. When a macroscopic system is exposed to intense laser fields whose forces are comparable to the binding forces of valence electrons, the system will emit coherent radiation with frequencies many times that of the driving laser field. This non-perturbativeand extremely nonlinear optical phenomenon is calledhigh-order harmonic generation, whichhas become a research direction of great concern in the field of strong field physicsas a Potential Extreme Ultraviolet (EUV) source and a possible means of real-time detection of ultrafast dynamics inside matter. In the past 30 years, HHG from gases has been developed greatly based on the physical image of the three-step model, which has laid a solid foundation for attosecond physics. HHG from solids provides a new way to miniaturize devices as a EUV light source and explore the electronic structure of condensed matter system. Meanwhile, in order to find more integrated and compact EUV light source, people gradually turn their attention to solid target.Experimental observation of non-perturbative transmitted high-order harmonics generated from ZnO crystal suggested that the solid-state HHG process can be illustrated neither by conventional perturbative nonlinear optics nor by the kinematics of strong-field re-scattering.More researches demonstrated that solid-state HHG can be achieved through a wide variety of interaction media with suitable laser wavelengths from the near-infrared to terahertz range.High harmonic generation from solid materials driven by an ultrafast strong laser is a fast developing direction in interdisciplinary fields of condensed matter physics, materials science, optics and photonics. So far, the target of solid-state HHG study has been expanded from bulk metals, semiconductors, insulators to low-dimensional nanostructures. Moreover, nonperturbative harmonic signals have been successfully detected in topological insulators and from topological surface states. Compared to gaseous atoms and molecules, solid materials have higher atomic density, and the mechanism of solid-state HHG is more complicated, thus solid-state HHG possesses good application prospects in achieving new light sources, exploring physical properties as well as characterizing microscopic dynamics of materials. This article mainly reviews the experimental and theoretical progresses of solid-state HHG in recent years, and also summarizes its mechanisms and potential applications.
Acta Photonica Sinica
- Publication Date: Aug. 25, 2022
- Vol. 51, Issue 8, 0851515 (2022)
In vivo Skull Optical Clearing Technique and its Applications（Invited）
Dongyu LI, Tingting YU, Jingtan ZHU, and Dan ZHU
In summary, the novel in vivo skull optical clearing technique provides an optical window for cortical observation without craniotomy. Over the past decades, with the development of technique, there are a variety of skull optical clearing windows available, each with its own characteristics. Through the skull optical clearing window, various modern optical imaging techniques have been used to noninvasively monitor neurovascular information. Up to now, the skull optical clearing window holds the advantages of high resolution, large scale, long-term observation, and is compatible with immediate observation, therefore has great potential in the research of brain science and related diseases. In summary, the novel in vivo skull optical clearing technique provides an optical window for cortical observation without craniotomy. Over the past decades, with the development of technique, there are a variety of skull optical clearing windows available, each with its own characteristics. Through the skull optical clearing window, various modern optical imaging techniques have been used to noninvasively monitor neurovascular information. Up to now, the skull optical clearing window holds the advantages of high resolution, large scale, long-term observation, and is compatible with immediate observation, therefore has great potential in the research of brain science and related diseases.
Acta Photonica Sinica
- Publication Date: Aug. 25, 2022
- Vol. 51, Issue 8, 0851514 (2022)
Ultrafast Two-dimensional Electronic Spectroscopy and Excited-state Dynamics（Invited）
Yin SONG, Ruidan ZHU, Shuang YU, Xiaojuan CHUAI, Lirong QIU, and Weiqian ZHAO
Ultrafast Two-Dimensional Electronic Spectroscopy (2DES) has emerged as a powerful tool to probe excited-state dynamics in photosynthesis, photovoltaic materials, quantum dots, and two-dimensional materials in recent years. Compared to one-dimensional time-resolved spectroscopy, 2DES not only contains one additional dimension to resolve excited-state dynamics but also provides rich information about homogeneous and inhomogeneous broadening, intermolecular coupling and coherent dynamics that are not fully accessible to the traditional third-order spectroscopic methods. Here we will briefly introduce the principle of 2DES from the basic concepts such as Fourier-transform linear spectroscopy, and transient grating. Subsequently, we will illustrate the applications of 2DES in the context of recent studies of spectral broadening in two-dimensional materials, and charge separation and coherent dynamics in photosynthesis and photovoltaic materials. Finally, we will discuss the remaining challenges and exciting future directions for the fields of 2DES. Ultrafast Two-Dimensional Electronic Spectroscopy (2DES) has emerged as a powerful tool to probe excited-state dynamics in photosynthesis, photovoltaic materials, quantum dots, and two-dimensional materials in recent years. Compared to one-dimensional time-resolved spectroscopy, 2DES not only contains one additional dimension to resolve excited-state dynamics but also provides rich information about homogeneous and inhomogeneous broadening, intermolecular coupling and coherent dynamics that are not fully accessible to the traditional third-order spectroscopic methods. Here we will briefly introduce the principle of 2DES from the basic concepts such as Fourier-transform linear spectroscopy, and transient grating. Subsequently, we will illustrate the applications of 2DES in the context of recent studies of spectral broadening in two-dimensional materials, and charge separation and coherent dynamics in photosynthesis and photovoltaic materials. Finally, we will discuss the remaining challenges and exciting future directions for the fields of 2DES.
Acta Photonica Sinica
- Publication Date: Aug. 25, 2022
- Vol. 51, Issue 8, 0851511 (2022)
Research Progress of Imaging Technology Based on Single Photon Avalanche Diode Arrays（Invited）
Mingjie SUN, and Zhiguan WANG
Single-photon avalanche diodes are widely used in various fields because of their single-photon sensitivity and excellent time-resolved performance. With the development of semiconductor technology, single-photon avalanche diode arrays integrating multiple pixels and time measurement circuits are gradually popularized, with the ability to collect photon information in parallel. Imaging is a means of obtaining information of the target object through photons, and imaging systems based on single-photon avalanche diodes can use richer photon counts and temporal information to detect the target in extreme environments. Single-photon avalanche diode arrays have higher detection efficiency, which can replace the detection system of single-pixel detectors and scanning structures, promoting the advancement of biological microscopy, scattering imaging and lidar technologies. This manuscript concludes the development of single-photon avalanche diode arrays and introduces some typical applications of single-photon avalanche diode arrays in imaging. The development of SPAD is similar to other photodetectors, which have gone through the process from single-point detectors to multi-pixel arrays. Because of the application of CMOS technology, SPAD arrays have developed rapidly in terms of pixel scale and circuit integration. Megapixel SPAD arrays with time measurement capabilities are available nowadays. While the pixel scale is gradually increasing, important parameters such as photon detection efficiency, dark count rate, spectral response range, and temporal resolution are also continuously optimized with the development of related technologies. Optical imaging has a long history. With the development of science and technology, people's research interests have gradually expanded from traditional imaging to imaging under extreme conditions, such as super-resolution imaging, extremely low-light imaging, and over-the-horizon imaging. SPAD has single-photon sensitivity and ps-level temporal resolution, which enables obtaining photon information under extreme conditions. As the performance of early SPAD arrays were not perfect, single-pixel SPAD detectors are often combined with a scanning device to obtain two-dimensional images. With the development of SPAD arrays, in applications that require real-time imaging, such as vehicle-based lidar, SPAD arrays have gradually replaced the scanning imaging systems because of their efficient parallel single-photon detection capabilities, providing higher imaging speed. Besides, many biophotonics applications have been explored with SPAD arrays, such as SMLM and FLIM. The use of SPAD arrays in these applications enables higher SNR, higher imaging speed, providing powerful method to investigate the structural details and molecular dynamics of cells. In addition, the high dynamic range images are accessible through a SPAD array, which has the potential to be applied in autonomous driving and object recognition. In scattering imaging and non-line-of-sight imaging, the emergence of SPAD arrays enables the complex photon propagation process caused by multipath, scattering or other factors to be distinguished in time domain and space domain, and the photon information can be combined with physical model or neural network to detect the target object which is outside the field of view or behind the scattering medium. Using the high temporal resolution and parallel acquisition capability of SPAD arrays, one can also track the high-speed laser pulses, providing more details of ultrafast optical phenomena. The low price and high integration of SPAD arrays are unmatched by other devices. In the future, if the cost of megapixel SPAD arrays can be reduced to a reasonable range, they will be widely used in scientific research, industry and military fields. However, the reported megapixel SPAD array is still in the laboratory verification stage, and there is still a long distance from the industrialization and commercialization. In addition, with the continuous increase of the pixel scale of SPAD arrays, the storage, processing and transmission of photonic data will be a difficult problem. Using high-performance FPGA to locally preprocess the photonic data can effectively reduce the demand for data storage, reducing the data transfer bandwidth between SPAD arrays and computers. In terms of spectral response, the spectral response peaks of silicon-based SPAD arrays are mainly within the visible light band. The photon detection probability of silicon-based SPAD arrays in the near-infrared band can be improved through structure and process optimization, enabling utilizing the strong penetration of near-infrared light to improve the detection range of lidar and scattering imaging. SPAD arrays based on InGaAs or InP can respond to short-wave infrared light above 1450 nm, so such SPAD arrays have great application potential in imaging with optical fibers and quantum optics. SPAD arrays can efficiently acquire spatiotemporal information of photons, and how to make full use of these photonic data is also a problem that needs to be solved in the application of SPAD arrays. In addition to establishing the physical model of photon propagation, data-driven algorithms such as deep learning can also be used to establish a correspondence between the spatiotemporal distribution of photon and target features from a higher dimension, enabling efficiently reveal the hidden information in the photonic data. In the future, SPAD arrays will play a more important role in optical imaging, providing more powerful tools to perceive and understand the world. Single-photon avalanche diodes are widely used in various fields because of their single-photon sensitivity and excellent time-resolved performance. With the development of semiconductor technology, single-photon avalanche diode arrays integrating multiple pixels and time measurement circuits are gradually popularized, with the ability to collect photon information in parallel. Imaging is a means of obtaining information of the target object through photons, and imaging systems based on single-photon avalanche diodes can use richer photon counts and temporal information to detect the target in extreme environments. Single-photon avalanche diode arrays have higher detection efficiency, which can replace the detection system of single-pixel detectors and scanning structures, promoting the advancement of biological microscopy, scattering imaging and lidar technologies. This manuscript concludes the development of single-photon avalanche diode arrays and introduces some typical applications of single-photon avalanche diode arrays in imaging. The development of SPAD is similar to other photodetectors, which have gone through the process from single-point detectors to multi-pixel arrays. Because of the application of CMOS technology, SPAD arrays have developed rapidly in terms of pixel scale and circuit integration. Megapixel SPAD arrays with time measurement capabilities are available nowadays. While the pixel scale is gradually increasing, important parameters such as photon detection efficiency, dark count rate, spectral response range, and temporal resolution are also continuously optimized with the development of related technologies. Optical imaging has a long history. With the development of science and technology, people's research interests have gradually expanded from traditional imaging to imaging under extreme conditions, such as super-resolution imaging, extremely low-light imaging, and over-the-horizon imaging. SPAD has single-photon sensitivity and ps-level temporal resolution, which enables obtaining photon information under extreme conditions. As the performance of early SPAD arrays were not perfect, single-pixel SPAD detectors are often combined with a scanning device to obtain two-dimensional images. With the development of SPAD arrays, in applications that require real-time imaging, such as vehicle-based lidar, SPAD arrays have gradually replaced the scanning imaging systems because of their efficient parallel single-photon detection capabilities, providing higher imaging speed. Besides, many biophotonics applications have been explored with SPAD arrays, such as SMLM and FLIM. The use of SPAD arrays in these applications enables higher SNR, higher imaging speed, providing powerful method to investigate the structural details and molecular dynamics of cells. In addition, the high dynamic range images are accessible through a SPAD array, which has the potential to be applied in autonomous driving and object recognition. In scattering imaging and non-line-of-sight imaging, the emergence of SPAD arrays enables the complex photon propagation process caused by multipath, scattering or other factors to be distinguished in time domain and space domain, and the photon information can be combined with physical model or neural network to detect the target object which is outside the field of view or behind the scattering medium. Using the high temporal resolution and parallel acquisition capability of SPAD arrays, one can also track the high-speed laser pulses, providing more details of ultrafast optical phenomena. The low price and high integration of SPAD arrays are unmatched by other devices. In the future, if the cost of megapixel SPAD arrays can be reduced to a reasonable range, they will be widely used in scientific research, industry and military fields. However, the reported megapixel SPAD array is still in the laboratory verification stage, and there is still a long distance from the industrialization and commercialization. In addition, with the continuous increase of the pixel scale of SPAD arrays, the storage, processing and transmission of photonic data will be a difficult problem. Using high-performance FPGA to locally preprocess the photonic data can effectively reduce the demand for data storage, reducing the data transfer bandwidth between SPAD arrays and computers. In terms of spectral response, the spectral response peaks of silicon-based SPAD arrays are mainly within the visible light band. The photon detection probability of silicon-based SPAD arrays in the near-infrared band can be improved through structure and process optimization, enabling utilizing the strong penetration of near-infrared light to improve the detection range of lidar and scattering imaging. SPAD arrays based on InGaAs or InP can respond to short-wave infrared light above 1450 nm, so such SPAD arrays have great application potential in imaging with optical fibers and quantum optics. SPAD arrays can efficiently acquire spatiotemporal information of photons, and how to make full use of these photonic data is also a problem that needs to be solved in the application of SPAD arrays. In addition to establishing the physical model of photon propagation, data-driven algorithms such as deep learning can also be used to establish a correspondence between the spatiotemporal distribution of photon and target features from a higher dimension, enabling efficiently reveal the hidden information in the photonic data. In the future, SPAD arrays will play a more important role in optical imaging, providing more powerful tools to perceive and understand the world.
Acta Photonica Sinica
- Publication Date: Aug. 25, 2022
- Vol. 51, Issue 8, 0851510 (2022)
Structure and Biomedical Applications of Small Molecular Super-resolution Fluorescent Imaging Dyes（Invited）
Lin LI, Duoteng ZHANG, and Yunwei QU
Finally, we look forward to the development direction of small molecule dyes and propose for novel super-resolution fluorescent dyes/probes to achieve high membrane permeability, excellent precision positioning ability, high brightness and stability, and low phototoxicity of dye molecules without increasing the size of dye molecules as much as possible. This paper summarized the structural design characteristics of organic small molecule dyes selected for different techniques with respect to the requirements of different super-resolution imaging techniques for dye performance. It provides ideas for the development of new dyes suitable for super-resolution imaging. Finally, we look forward to the development direction of small molecule dyes and propose for novel super-resolution fluorescent dyes/probes to achieve high membrane permeability, excellent precision positioning ability, high brightness and stability, and low phototoxicity of dye molecules without increasing the size of dye molecules as much as possible. This paper summarized the structural design characteristics of organic small molecule dyes selected for different techniques with respect to the requirements of different super-resolution imaging techniques for dye performance. It provides ideas for the development of new dyes suitable for super-resolution imaging.
Acta Photonica Sinica
- Publication Date: Aug. 25, 2022
- Vol. 51, Issue 8, 0851509 (2022)
Harnessing the Power of Bessel Beam for Biomedical Microscopy（Invited）
Xueli CHEN, Xinyu WANG, Tianyu YAN, Qi ZENG, Xinyi XU, and Hui XIE
This paper firstly outlines the concept and characteristics of Bessel beams, as well as the commonly used laboratory generation methods, including the generation using a ring slit, using an axicon, and using a spatial light modulator, etc. The authors then summarize the applications of the Bessel beams in biomedical optical microscopy techniques in recent years, focusing on their applications in the fields of multiphoton fluorescence microscopy, light-sheet fluorescence microimaging, Raman microimaging, and other techniques. The authors summarize the advantages of Bessel beams, including extended depth-of-field imaging based on diffraction-free properties, large-depth imaging based on self-reconfiguration properties, and high-resolution imaging based on finer-focused beams, and also analyze the solutions to eliminate the interference problems caused by side rings of the Bessel beam. In addition, the authors also briefly describe the exploration and application of Bessel beams in other imaging modalities, including the technical areas of optical coherent tomography, optical coherent elastography, photoacoustic imaging, second harmonic imaging, third harmonic imaging, and Fourier multiplexed fluorescence lifetime tomographic imaging. The article concludes with an analysis and discussion of the problems encountered in the application of Bessel beams in biomedical optical microscopy and the prospects for development. This paper firstly outlines the concept and characteristics of Bessel beams, as well as the commonly used laboratory generation methods, including the generation using a ring slit, using an axicon, and using a spatial light modulator, etc. The authors then summarize the applications of the Bessel beams in biomedical optical microscopy techniques in recent years, focusing on their applications in the fields of multiphoton fluorescence microscopy, light-sheet fluorescence microimaging, Raman microimaging, and other techniques. The authors summarize the advantages of Bessel beams, including extended depth-of-field imaging based on diffraction-free properties, large-depth imaging based on self-reconfiguration properties, and high-resolution imaging based on finer-focused beams, and also analyze the solutions to eliminate the interference problems caused by side rings of the Bessel beam. In addition, the authors also briefly describe the exploration and application of Bessel beams in other imaging modalities, including the technical areas of optical coherent tomography, optical coherent elastography, photoacoustic imaging, second harmonic imaging, third harmonic imaging, and Fourier multiplexed fluorescence lifetime tomographic imaging. The article concludes with an analysis and discussion of the problems encountered in the application of Bessel beams in biomedical optical microscopy and the prospects for development.
Acta Photonica Sinica
- Publication Date: Aug. 25, 2022
- Vol. 51, Issue 8, 0851508 (2022)
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