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Ultrafast Optics|8 Article(s)
Research on Driving Technology of Wide Microstrip Amplitude Division Imaging Based on Pulse Power Synthesis Technology
Shiduo WEI, Yongsheng GOU, Yang YANG, Penghui FENG, Baiyu LIU, Jinshou TIAN, Xu WANG, Hengbo LIU, Hantao XU, and Yihao YANG
When a pulse current with a rise time of about 100 ns and an amplitude of tens of MA is applied to a wire array or jet load, the load will rapidly ionize and form a plasma. Due to the Lorentzian force, these plasms will rapidly implode towards the axis and eventually stagnate in the center, forming a high temperature and high density plasma and further emitting strong X-rays, a process known as Z-pinch. Z-pinch has been widely used in High Energy Density (HED) physics research for decades, including radiation source development, radiation actuation science, dynamic material properties, Magneto-inertial Fusion (MIF) and Inertial Confinement Fusion (ICF). In order to explore the structure, properties and motion laws of matter in the ultra-small space and ultra-fast time scale, the research and measurement techniques of ultra-fast phenomena represented by the variometer framing camera technology have become the main tools in use.X-ray framing cameras are widely used for two-dimensional plasma imaging in the Z-pinch process. This type of frame camera requires selective pulses to excite the Microchannel Plate (MCP). Because the width of the pulse is very narrow, only a microstrip region has voltage at a time, and photoelectrons generated by the X-ray image formed through a pinhole in the region at the input surface of the MCP will be gained and be imaged to the screen on the screen. The exposure time of each image is determined by the half-width of the selected pulse and the characteristics of the framing tube. The MCP with different equivalent impedances will realize the framing camera imaging with different frames. The width and length of the transmission microstrip line of the ultra-wide frame traveling-wave selective framing camera are up to 20 mm and 95 mm, and the equivalent impedance is about 6 Ω. To actuate the beamsplitter, gating pulses with electric field peaks of more than 3 kV, pulse durations on the order of nanoseconds or hundreds of picoseconds, and spectral widths of tens to thousands of megahertz is required. In this paper, the power coupling method based on Wilkinson structure power splitter is adopted to synthesize the narrow-band pulse with low amplitude into the high-voltage pulse with the required amplitude. However, limited by the characteristics of the transistor device itself, the pulse source whose amplitude is higher than 5 kV and the front edge is better than 100 ps and the jitter is better than 20 ps is close to the technical limit of electronics. To obtain higher power gate pulse it is necessary to adopt multichannel pulse power synthesis technology.In this paper, a power coupling method based on Wilkinson structure power splitter is adopted to synthesize the narrow-band pulse with low amplitude into the high-voltage pulse with the required amplitude. The large bandwidth of the multi-section impedance converter is used to improve the working bandwidth of the power coupling, so as to meet the pulse coupling of different spectrum. The simulation software is used to design the power coupling circuit with the working frequency band of 300 MHz~3 GHz, and the loss generated in the system is optimized to achieve high efficiency coupling. Combined with the high-voltage narrow pulse output and synchronization control circuit of the preceding stage, the high-voltage pulse with peak voltage exceeding 3.2 kV is synthesized by using eight single-channel pulses with peak voltage of about 1.3 kV and pulse width of about 3.5 ns, pulse leading edge of about 600 ps. The pulse width was within 3 ns and the pulse leading edge was within 600 ps. In the pulse spectrum range of 300 MHz to 3 GHz, the two-channel synthesis efficiency is 83.5%, 88% at a specific frequency, and the eight-channel synthesis efficiency is 58%, up to 68% at a specific frequency.Finally, the coupled high-voltage pulse is input into the 20 mm microstrip amplitude-divider. The transmission line of the microchannel plate inside is 20 mm wide and 95 mm long, and the equivalent impedance is 6 Ω. The output pulse amplitude is 1.433 kV, the pulse width is 3.63 ns, and the pulse front is 747.3 ps, which fully conforms to the design requirement that the output voltage of the tube must exceed 800 V. At present, the coupling technique can generate driving pulses for use. In the future, the coupled pulses can be shaped by adjusting the delay of the eight pulses. At present, the high voltage driven pulse source based on this technology has been applied to I-MCP1.0 framing camera and can be used to explore the high energy density physics research with Z-pinch as the core. When a pulse current with a rise time of about 100 ns and an amplitude of tens of MA is applied to a wire array or jet load, the load will rapidly ionize and form a plasma. Due to the Lorentzian force, these plasms will rapidly implode towards the axis and eventually stagnate in the center, forming a high temperature and high density plasma and further emitting strong X-rays, a process known as Z-pinch. Z-pinch has been widely used in High Energy Density (HED) physics research for decades, including radiation source development, radiation actuation science, dynamic material properties, Magneto-inertial Fusion (MIF) and Inertial Confinement Fusion (ICF). In order to explore the structure, properties and motion laws of matter in the ultra-small space and ultra-fast time scale, the research and measurement techniques of ultra-fast phenomena represented by the variometer framing camera technology have become the main tools in use.X-ray framing cameras are widely used for two-dimensional plasma imaging in the Z-pinch process. This type of frame camera requires selective pulses to excite the Microchannel Plate (MCP). Because the width of the pulse is very narrow, only a microstrip region has voltage at a time, and photoelectrons generated by the X-ray image formed through a pinhole in the region at the input surface of the MCP will be gained and be imaged to the screen on the screen. The exposure time of each image is determined by the half-width of the selected pulse and the characteristics of the framing tube. The MCP with different equivalent impedances will realize the framing camera imaging with different frames. The width and length of the transmission microstrip line of the ultra-wide frame traveling-wave selective framing camera are up to 20 mm and 95 mm, and the equivalent impedance is about 6 Ω. To actuate the beamsplitter, gating pulses with electric field peaks of more than 3 kV, pulse durations on the order of nanoseconds or hundreds of picoseconds, and spectral widths of tens to thousands of megahertz is required. In this paper, the power coupling method based on Wilkinson structure power splitter is adopted to synthesize the narrow-band pulse with low amplitude into the high-voltage pulse with the required amplitude. However, limited by the characteristics of the transistor device itself, the pulse source whose amplitude is higher than 5 kV and the front edge is better than 100 ps and the jitter is better than 20 ps is close to the technical limit of electronics. To obtain higher power gate pulse it is necessary to adopt multichannel pulse power synthesis technology.In this paper, a power coupling method based on Wilkinson structure power splitter is adopted to synthesize the narrow-band pulse with low amplitude into the high-voltage pulse with the required amplitude. The large bandwidth of the multi-section impedance converter is used to improve the working bandwidth of the power coupling, so as to meet the pulse coupling of different spectrum. The simulation software is used to design the power coupling circuit with the working frequency band of 300 MHz~3 GHz, and the loss generated in the system is optimized to achieve high efficiency coupling. Combined with the high-voltage narrow pulse output and synchronization control circuit of the preceding stage, the high-voltage pulse with peak voltage exceeding 3.2 kV is synthesized by using eight single-channel pulses with peak voltage of about 1.3 kV and pulse width of about 3.5 ns, pulse leading edge of about 600 ps. The pulse width was within 3 ns and the pulse leading edge was within 600 ps. In the pulse spectrum range of 300 MHz to 3 GHz, the two-channel synthesis efficiency is 83.5%, 88% at a specific frequency, and the eight-channel synthesis efficiency is 58%, up to 68% at a specific frequency.Finally, the coupled high-voltage pulse is input into the 20 mm microstrip amplitude-divider. The transmission line of the microchannel plate inside is 20 mm wide and 95 mm long, and the equivalent impedance is 6 Ω. The output pulse amplitude is 1.433 kV, the pulse width is 3.63 ns, and the pulse front is 747.3 ps, which fully conforms to the design requirement that the output voltage of the tube must exceed 800 V. At present, the coupling technique can generate driving pulses for use. In the future, the coupled pulses can be shaped by adjusting the delay of the eight pulses. At present, the high voltage driven pulse source based on this technology has been applied to I-MCP1.0 framing camera and can be used to explore the high energy density physics research with Z-pinch as the core.
Acta Photonica Sinica
- Publication Date: Sep. 25, 2023
- Vol. 52, Issue 9, 0932002 (2023)
Generation of Femtosecond Magnetic Pulses by Circularly Polarized Vortex Laser-driven Plasma
Han WEN, Peng XU, Liangwen PI, and Yuxi FU
Research on pulsed magnetic fields dates back to the early 20th century. Nowadays, ultra-short pulsed magnetic fields are being utilized to better understand ultrafast physical microprocesses, such as domain motion and spin-orbit interaction, with time scales ranging from microseconds to femtoseconds. In particular, femtosecond magnetic field pulses are of great significance for studying ultrafast magnetization, ultrafast demagnetization, ultrafast magnetic storage, and spin ultrafast dynamics. However, traditional pulsed magnetic fields are limited by the performance of the pulse power supply and the mechanical strength of the coil and cannot achieve higher pulsed magnetic field strengths. Additionally, the pulse length of the magnetic pulse generated by the pulse power supply is at the millisecond level, which makes it unsuitable for studying faster magnetic dynamics processes. Fortunately, recent studies have shown that when ultra-short pulse lasers interact with plasmas, hot electrons are produced on the surface of the plasma target. These hot electrons are then excited and pass through the target material, producing strong charge separation on the back surface of the target material. Under the action of the laser, these excited electrons are accelerated, generating strong electromagnetic radiation. Consequently, using ultra-short pulse lasers to drive electron flows is currently the most promising method for generating femtosecond magnetic field pulses. Thus, the goal of this paper is to use a three-dimensional model to simulate the interaction between the driving optical field and the plasma target. This simulation will help to study the physical processes involved, such as the propagation of the optical field, the movement of free electrons, vortex currents, and pulse magnetic field generation. By optimizing the relevant parameters, this research aims to generate femtosecond magnetic field pulses.In this paper, we employ the Particle-In-Cell (PIC) method as our simulation approach. This method utilizes the Vlasov-Maxwell equation set to accurately describe the self-consistent dynamics in plasma simulation. The electrons in the plasma are subject to the Lorenz force, which generates new current density as they move. This equation effectively corrects the electric and magnetic fields through the charge density and current density. The driving light described is a circularly polarized vortex beam, with a wavelength of 800 nm and an optical field intensity of approximately 1016 to 1021 W/cm2. The pulse width of the beam is roughly 10 fs. The plasma density ranges from 1018 to 1020 cm-3, and is confined within a cubic space with a side length of 30 λ0. During the simulation process, we only consider refractive index changes due to electron density and do not account for non-linear effects. Additionally, we assume that the ions are stationary and that the initial velocity and temperature of the plasma are both 0.During theoretical simulation, a proportionality gradient between momentum potential and the strength of the light field is created due to the lowest intensity of the vortex beam at its center. This gradient then forms a potential well, preventing electrons from escaping outward and producing a structured electron beam with a femtosecond duration. In addition, particles acquire angular momentum in their radial motion within the laser field, generating a vortex current. This in turn produces a pulsed magnetic field based on the current magnetic effect.The simulation results indicate that when circularly polarized vortex beams, with light field intensities of the order of 1016 to 1021 W/cm2, interact with plasma densities ranging from 1018 to 1020 cm-3, they can generate ultra-short magnetic pulses with peak intensities of 0.5~50 tesla and pulse time widths of about 10 fs. The effects of driving laser intensity and plasma density on these magnetic pulses are discussed through a simulated system calculation. The results show that the pulsed magnetic field intensity is proportional to the square root of both laser intensity and plasma density. Increasing electron density and laser intensity may facilitate the generation of ultra-short strong magnetic fields, providing numerical references for the production of femtosecond magnetic pulses in experiments.We expect that the simulation results above will facilitate the introduction of ultra-strong, ultra-short magnetic pulses into the femtosecond ultrafast realm, thereby supporting the advancement of research on ultrafast magnetic and spin dynamics, electronic motion and spin microprocessing control, ultrafast spin-electron magnetic storage applications, and magnetic switching. Research on pulsed magnetic fields dates back to the early 20th century. Nowadays, ultra-short pulsed magnetic fields are being utilized to better understand ultrafast physical microprocesses, such as domain motion and spin-orbit interaction, with time scales ranging from microseconds to femtoseconds. In particular, femtosecond magnetic field pulses are of great significance for studying ultrafast magnetization, ultrafast demagnetization, ultrafast magnetic storage, and spin ultrafast dynamics. However, traditional pulsed magnetic fields are limited by the performance of the pulse power supply and the mechanical strength of the coil and cannot achieve higher pulsed magnetic field strengths. Additionally, the pulse length of the magnetic pulse generated by the pulse power supply is at the millisecond level, which makes it unsuitable for studying faster magnetic dynamics processes. Fortunately, recent studies have shown that when ultra-short pulse lasers interact with plasmas, hot electrons are produced on the surface of the plasma target. These hot electrons are then excited and pass through the target material, producing strong charge separation on the back surface of the target material. Under the action of the laser, these excited electrons are accelerated, generating strong electromagnetic radiation. Consequently, using ultra-short pulse lasers to drive electron flows is currently the most promising method for generating femtosecond magnetic field pulses. Thus, the goal of this paper is to use a three-dimensional model to simulate the interaction between the driving optical field and the plasma target. This simulation will help to study the physical processes involved, such as the propagation of the optical field, the movement of free electrons, vortex currents, and pulse magnetic field generation. By optimizing the relevant parameters, this research aims to generate femtosecond magnetic field pulses.In this paper, we employ the Particle-In-Cell (PIC) method as our simulation approach. This method utilizes the Vlasov-Maxwell equation set to accurately describe the self-consistent dynamics in plasma simulation. The electrons in the plasma are subject to the Lorenz force, which generates new current density as they move. This equation effectively corrects the electric and magnetic fields through the charge density and current density. The driving light described is a circularly polarized vortex beam, with a wavelength of 800 nm and an optical field intensity of approximately 1016 to 1021 W/cm2. The pulse width of the beam is roughly 10 fs. The plasma density ranges from 1018 to 1020 cm-3, and is confined within a cubic space with a side length of 30 λ0. During the simulation process, we only consider refractive index changes due to electron density and do not account for non-linear effects. Additionally, we assume that the ions are stationary and that the initial velocity and temperature of the plasma are both 0.During theoretical simulation, a proportionality gradient between momentum potential and the strength of the light field is created due to the lowest intensity of the vortex beam at its center. This gradient then forms a potential well, preventing electrons from escaping outward and producing a structured electron beam with a femtosecond duration. In addition, particles acquire angular momentum in their radial motion within the laser field, generating a vortex current. This in turn produces a pulsed magnetic field based on the current magnetic effect.The simulation results indicate that when circularly polarized vortex beams, with light field intensities of the order of 1016 to 1021 W/cm2, interact with plasma densities ranging from 1018 to 1020 cm-3, they can generate ultra-short magnetic pulses with peak intensities of 0.5~50 tesla and pulse time widths of about 10 fs. The effects of driving laser intensity and plasma density on these magnetic pulses are discussed through a simulated system calculation. The results show that the pulsed magnetic field intensity is proportional to the square root of both laser intensity and plasma density. Increasing electron density and laser intensity may facilitate the generation of ultra-short strong magnetic fields, providing numerical references for the production of femtosecond magnetic pulses in experiments.We expect that the simulation results above will facilitate the introduction of ultra-strong, ultra-short magnetic pulses into the femtosecond ultrafast realm, thereby supporting the advancement of research on ultrafast magnetic and spin dynamics, electronic motion and spin microprocessing control, ultrafast spin-electron magnetic storage applications, and magnetic switching.
Acta Photonica Sinica
- Publication Date: Sep. 25, 2023
- Vol. 52, Issue 9, 0932001 (2023)
Excitation and Ionization Dynamics of Atomic Rydberg States in Strong Laser Field（Invited）
Yong ZHAO, and Yueming ZHOU
When atoms are exposed to strong femtosecond laser fields, there is a high probability that the electrons in atoms can be excited to the Rydberg states with very high principal quantum numbers and large orbitals, in addition to processes such as multiphoton ionization and tunneling ionization. This highly excited state of the atom is very stable in the ultrashort strong laser pulse and is closely related to many other phenomena in the strong field, such as neutral particle acceleration, multiphoton Rabi oscillations, near-threshold harmonic radiation. It has become one of the research hotspots in the field of strong-field ultrafast physics in the last decade. Among these studies, the mechanism of the generation of Rydberg atoms in strong laser fields, the modulation of Rydberg states by lasers, and the strong-field ionization process and stability of Rydberg states are the main issues of interest.This review provided an overview of the generation mechanisms of the Rydberg states driven by strong laser fields. There are two mechanisms for strong field Rydberg state excitation. One is multiphoton resonance excitation and the other is Frustrated Tunneling Ionization (FTI) excitation. The dependence of the yield of the Rydberg state atoms on the laser ellipticity is usually considered to be an important basis for determining whether the Rydberg state atom generation mechanism is multiphoton resonance excitation or frustrated tunneling ionization. However, this judgment is not reliable. As shown in this review, for multiphoton resonance excitation, the yield of Rydberg state atoms also decreases rapidly with increasing laser ellipticity. In contrast, in the nonadiabatic tunneling ionization region, the yield of Rydberg state atoms in FTI does not always decrease with increasing laser ellipticity, instead, it shows an abnormal increase in the yield. There is no clear boundary between these two mechanisms.This review focused on a variety of interference phenomena during the Rydberg-state excitation of atoms driven by strong laser fields, which are manifested as oscillations of the Rydberg state atomic yield with laser intensity. These interference phenomena are classified into three categories according to the magnitude of the as-Stark shift corresponding to the laser intensity interval of the oscillation period. The first category is the interference with an oscillation period of one photon energy. In multiphoton resonance excitation images, this interference can be understood as channel closing. In tunneling images, it can be understood as coherent recapture, wherein the electrons tunneling ionize at different laser cycles, are recaptured, and interfere, giving rising to the laser-intensity-dependent oscillation of the excitation yield. The second category is the interference with oscillation periods much larger than one photon energy, which usually appears in the long wavelength region. This type of oscillation is explained as the interference of the tunneling electron recaptured at different returns. The third category is the interference with oscillation period much smaller than one photon energy, due to the interference of the excitation during the rising and falling edges of the laser pulse, i.e., the dynamic interference. These interference phenomena provide the dynamic information of the strong-field excitation process of the Rydberg-state atom.In this review, the ionization processes of excited atoms in strong laser fields are also presented, in particular, the circular dichroism of ionization of the Rydberg atoms driven by circularly polarized laser fields. Because of this circular dichroism, the Rydberg state can be considered as the simplest chiral system, which is important for one to explore the chirality of molecules. In addition, the circular dichroism of Rydberg state atoms is also important for the preparing and detecting high-purity single ring current states at ultrafast time scales and the generation of spin-polarized electron pulses. When atoms are exposed to strong femtosecond laser fields, there is a high probability that the electrons in atoms can be excited to the Rydberg states with very high principal quantum numbers and large orbitals, in addition to processes such as multiphoton ionization and tunneling ionization. This highly excited state of the atom is very stable in the ultrashort strong laser pulse and is closely related to many other phenomena in the strong field, such as neutral particle acceleration, multiphoton Rabi oscillations, near-threshold harmonic radiation. It has become one of the research hotspots in the field of strong-field ultrafast physics in the last decade. Among these studies, the mechanism of the generation of Rydberg atoms in strong laser fields, the modulation of Rydberg states by lasers, and the strong-field ionization process and stability of Rydberg states are the main issues of interest.This review provided an overview of the generation mechanisms of the Rydberg states driven by strong laser fields. There are two mechanisms for strong field Rydberg state excitation. One is multiphoton resonance excitation and the other is Frustrated Tunneling Ionization (FTI) excitation. The dependence of the yield of the Rydberg state atoms on the laser ellipticity is usually considered to be an important basis for determining whether the Rydberg state atom generation mechanism is multiphoton resonance excitation or frustrated tunneling ionization. However, this judgment is not reliable. As shown in this review, for multiphoton resonance excitation, the yield of Rydberg state atoms also decreases rapidly with increasing laser ellipticity. In contrast, in the nonadiabatic tunneling ionization region, the yield of Rydberg state atoms in FTI does not always decrease with increasing laser ellipticity, instead, it shows an abnormal increase in the yield. There is no clear boundary between these two mechanisms.This review focused on a variety of interference phenomena during the Rydberg-state excitation of atoms driven by strong laser fields, which are manifested as oscillations of the Rydberg state atomic yield with laser intensity. These interference phenomena are classified into three categories according to the magnitude of the as-Stark shift corresponding to the laser intensity interval of the oscillation period. The first category is the interference with an oscillation period of one photon energy. In multiphoton resonance excitation images, this interference can be understood as channel closing. In tunneling images, it can be understood as coherent recapture, wherein the electrons tunneling ionize at different laser cycles, are recaptured, and interfere, giving rising to the laser-intensity-dependent oscillation of the excitation yield. The second category is the interference with oscillation periods much larger than one photon energy, which usually appears in the long wavelength region. This type of oscillation is explained as the interference of the tunneling electron recaptured at different returns. The third category is the interference with oscillation period much smaller than one photon energy, due to the interference of the excitation during the rising and falling edges of the laser pulse, i.e., the dynamic interference. These interference phenomena provide the dynamic information of the strong-field excitation process of the Rydberg-state atom.In this review, the ionization processes of excited atoms in strong laser fields are also presented, in particular, the circular dichroism of ionization of the Rydberg atoms driven by circularly polarized laser fields. Because of this circular dichroism, the Rydberg state can be considered as the simplest chiral system, which is important for one to explore the chirality of molecules. In addition, the circular dichroism of Rydberg state atoms is also important for the preparing and detecting high-purity single ring current states at ultrafast time scales and the generation of spin-polarized electron pulses.
Acta Photonica Sinica
- Publication Date: Jul. 25, 2023
- Vol. 52, Issue 7, 0732001 (2023)
High-gain Ultra-small Streak Camera and Its Integrated Control System
Yuchi ZHANG, Jinshou TIAN, Yanhua XUE, Zhibing LI, Shaohui LI, Junfeng WANG, Baiyu LIU, Guilong GAO, Ping CHEN, Xing WANG, and Wei ZHAO
As a diagnostic instrument with ultra-high temporal and spatial resolution and spectral resolution, the streak camera is widely used in basic research fields such as physics, life sciences, and materials science, as well as in national strategic fields such as detonation physics, lidar, and inertial confinement fusion. Aiming at the requirements of airborne lidar for miniaturized, high-sensitivity, high-gain, and high spatiotemporal resolution streak camera, a high-brightness-gain compact streak camera and its new integrated control system are developed.Compared with the general picosecond visible light streak camera, the volume and weight of the camera are reduced by more than 2/3. The selected streak camera adopts the theoretical simulation research of cathode semiconductor and the method of optimizing the process to greatly improve the sensitivity of the cathode. Using a slit acceleration grid improves the photoelectron transmittance, enhances the photoelectron energy to give the fluorescent screen higher luminous efficiency, and optimizes the cathode process to improve the brightness gain. The streak image tube has the characteristics of high sensitivity, large detection field, high brightness gain, and high temporal and spatial resolution.Starting from the principle and control requirements, combined with the theoretical analysis of the defects of the active control system, a new type of high-integration control system is developed for the camera, which fully eliminates the low integration, poor reliability and compatibility of the previous version. defect. The hardware of the new control system adopts the design method of modularization and function reuse, and the PCB adopts the multi-layer board design. Compared with the current version, the degree of integration is increased by 2.36 times to achieve multi-device compatibility. The bottom layer of the system hardware is divided into main control module, power supply module, A/D module, D/A module, digital I/O and extended scan switching module: the main control module takes STM32F107VCT6 as the core and is responsible for the information between each module and the host computer Interaction; the power supply module is divided into a high-voltage power supply part and a low-voltage power supply part, which provide corresponding voltages for the stripe tube and each element of the circuit; the A/D module takes ADS1256 as the core, adds anti-static protection and digital-analog isolation to entirely eliminate noise interference, and uses SPI The protocol communicates with the host computer; the D/A module takes DAC8534 as the core to control the output of analog devices such as MCP and high-voltage power supply; the digital I/O and expansion scan switching module use the microcontroller GPIO as the control, and the 24 pins programmable interface supports function multiplexing. The PC-side visualization system realizes human-computer interaction and has functions such as camera control, instant feedback of collected images and data, and operation logs. The interface is concise and optimized, which greatly enhances the operability and maintainability of the camera.Finally, the streak tube static test system is used to test the parameters of the streak image tube: the cathode integral sensitivity is 268 μA/lm, the brightness gain is 20.1, and the time resolution is 36 ps; femtosecond laser, F-P etalon, DG645 delayer, oscilloscope, etc. built a dynamic test system for streak camera, and tested the static/dynamic spatial resolution, time resolution, control system function, etc. of the whole machine. The static spatial resolution is higher than 26 lp/mm, the full-screen scanning time is 600 ps, and the functions of control, monitoring and information exchange of the control system are normal. The developed streak camera works well in the laser radar and Inertial Confinement Fusion (ICF) picosecond laser targeting experiments. As a diagnostic instrument with ultra-high temporal and spatial resolution and spectral resolution, the streak camera is widely used in basic research fields such as physics, life sciences, and materials science, as well as in national strategic fields such as detonation physics, lidar, and inertial confinement fusion. Aiming at the requirements of airborne lidar for miniaturized, high-sensitivity, high-gain, and high spatiotemporal resolution streak camera, a high-brightness-gain compact streak camera and its new integrated control system are developed.Compared with the general picosecond visible light streak camera, the volume and weight of the camera are reduced by more than 2/3. The selected streak camera adopts the theoretical simulation research of cathode semiconductor and the method of optimizing the process to greatly improve the sensitivity of the cathode. Using a slit acceleration grid improves the photoelectron transmittance, enhances the photoelectron energy to give the fluorescent screen higher luminous efficiency, and optimizes the cathode process to improve the brightness gain. The streak image tube has the characteristics of high sensitivity, large detection field, high brightness gain, and high temporal and spatial resolution.Starting from the principle and control requirements, combined with the theoretical analysis of the defects of the active control system, a new type of high-integration control system is developed for the camera, which fully eliminates the low integration, poor reliability and compatibility of the previous version. defect. The hardware of the new control system adopts the design method of modularization and function reuse, and the PCB adopts the multi-layer board design. Compared with the current version, the degree of integration is increased by 2.36 times to achieve multi-device compatibility. The bottom layer of the system hardware is divided into main control module, power supply module, A/D module, D/A module, digital I/O and extended scan switching module: the main control module takes STM32F107VCT6 as the core and is responsible for the information between each module and the host computer Interaction; the power supply module is divided into a high-voltage power supply part and a low-voltage power supply part, which provide corresponding voltages for the stripe tube and each element of the circuit; the A/D module takes ADS1256 as the core, adds anti-static protection and digital-analog isolation to entirely eliminate noise interference, and uses SPI The protocol communicates with the host computer; the D/A module takes DAC8534 as the core to control the output of analog devices such as MCP and high-voltage power supply; the digital I/O and expansion scan switching module use the microcontroller GPIO as the control, and the 24 pins programmable interface supports function multiplexing. The PC-side visualization system realizes human-computer interaction and has functions such as camera control, instant feedback of collected images and data, and operation logs. The interface is concise and optimized, which greatly enhances the operability and maintainability of the camera.Finally, the streak tube static test system is used to test the parameters of the streak image tube: the cathode integral sensitivity is 268 μA/lm, the brightness gain is 20.1, and the time resolution is 36 ps; femtosecond laser, F-P etalon, DG645 delayer, oscilloscope, etc. built a dynamic test system for streak camera, and tested the static/dynamic spatial resolution, time resolution, control system function, etc. of the whole machine. The static spatial resolution is higher than 26 lp/mm, the full-screen scanning time is 600 ps, and the functions of control, monitoring and information exchange of the control system are normal. The developed streak camera works well in the laser radar and Inertial Confinement Fusion (ICF) picosecond laser targeting experiments.
Acta Photonica Sinica
- Publication Date: Oct. 25, 2022
- Vol. 51, Issue 10, 1032003 (2022)
Optimal Control of Isolated Attosecond Pulse Generation in an Ar Crystal（Invited）
Suna PANG, and Feng WANG
The ultrafast motion of electrons in atoms, molecules, and condensed matter can generally involve attosecond timescales. Attosecond light pulse can provide unusual functionalities for probing, initiating, driving, and controlling the ultrafast electronic dynamics with unprecedented high temporal and spatial resolutions simultaneously. The progress of attosecond science is closely linked to the improvement of attosecond light sources in terms of shorter and more intense attosecond pulses. Indeed, following its first synthesis and characterization, with the tendency towards reducing the pulse durations and increasing the pulse intensities, attosecond light pulses have and will continue to open up new venues for studying both fundamental and applied sciences, enabling a number of exciting possibilities.Over the last decade, people have conducted a lot of explorations on new methods of generating single attosecond pulses both experimentally and theoretically. In principle, an isolated attosecond light pulse can be generated via HHG originating from coherent electron motion in atoms, molecules, clusters and bulk crystals exposed to intense few-cycle femtosecond laser pulses. Theoretically, HHG in the atomic case can be well understood in the framework of a semi-classical model consisting of three steps. First, an electron is ionized into the continuum by tunneling through the potential barrier formed by the atomic Coulomb field and the driving laser field. Then, the ionized electron gains energy while being accelerated by the driving laser field. Finally, the electron recombines to the parent ion with an energy release in the form of harmonic photons. The generated harmonic radiation that occurs on successive half-cycles of the driving laser is coherent, leading to the emission of odd harmonics. Ultrashort attosecond pulse can be obtained only when the low-harmonic orders are filtered out. In the last two decades, almost all advances in isolated attosecond laser sources were based on HHG from atoms exposed to intense driving laser pulses. The main problem of isolated attosecond pulse generated by HHG in atoms is its weak intensity and low generation efficiency. To increase the strength of isolated pulses, laser-crystal interaction may be an alternative method worth investigating because in bulk crystals the existence of multiple ionization and recombination sites, the high density and periodic structure makes for richer dynamics allowing the possibility of higher conversion efficiency. At present, it is safe to say that while HHG in atomic gases has been explored extensively, much less has been done for bulk crystals. Interestingly enough, NDABASHIMIYE G et al. reported a direct comparison of HHG in the solid and gas phases of Ar. They found that the HHG spectra of the noble gas solids exhibit multiple platforms, well beyond the atomic limits of the corresponding gas phase harmonics measured under similar conditions, implying that shorter attosecond pulses could be realized in solids. What is most interesting to us is that the dependence of HHG on the laser polarization direction with respect to the Ar crystal, which are currently little studied. We theoretically investigated optimal control of isolated attosecond pulse generation in an Ar crystal irradiated by few-cycle femtosecond pulse, employing quantum time-dependent density-functional theory method. We explored systematically the effect of different laser polarization directions on isolated attosecond pulses generation, showing that the laser polarization direction with respect to the crystal is a sensitive control parameter for producing isolated attosecond pulses. The results indicate that for an Ar crystal, the intensity of isolated attosecond pulses is maximal at an optimal laser polarization direction with respect to the crystal, demonstrating about 11-fold intensity enhancement compared with that generated in an Ar atom under the same driving laser pulses. Our results also suggest opportunities for future investigations for the optimal control of isolated attosecond pulse generation in bulk crystal solids. The ultrafast motion of electrons in atoms, molecules, and condensed matter can generally involve attosecond timescales. Attosecond light pulse can provide unusual functionalities for probing, initiating, driving, and controlling the ultrafast electronic dynamics with unprecedented high temporal and spatial resolutions simultaneously. The progress of attosecond science is closely linked to the improvement of attosecond light sources in terms of shorter and more intense attosecond pulses. Indeed, following its first synthesis and characterization, with the tendency towards reducing the pulse durations and increasing the pulse intensities, attosecond light pulses have and will continue to open up new venues for studying both fundamental and applied sciences, enabling a number of exciting possibilities.Over the last decade, people have conducted a lot of explorations on new methods of generating single attosecond pulses both experimentally and theoretically. In principle, an isolated attosecond light pulse can be generated via HHG originating from coherent electron motion in atoms, molecules, clusters and bulk crystals exposed to intense few-cycle femtosecond laser pulses. Theoretically, HHG in the atomic case can be well understood in the framework of a semi-classical model consisting of three steps. First, an electron is ionized into the continuum by tunneling through the potential barrier formed by the atomic Coulomb field and the driving laser field. Then, the ionized electron gains energy while being accelerated by the driving laser field. Finally, the electron recombines to the parent ion with an energy release in the form of harmonic photons. The generated harmonic radiation that occurs on successive half-cycles of the driving laser is coherent, leading to the emission of odd harmonics. Ultrashort attosecond pulse can be obtained only when the low-harmonic orders are filtered out. In the last two decades, almost all advances in isolated attosecond laser sources were based on HHG from atoms exposed to intense driving laser pulses. The main problem of isolated attosecond pulse generated by HHG in atoms is its weak intensity and low generation efficiency. To increase the strength of isolated pulses, laser-crystal interaction may be an alternative method worth investigating because in bulk crystals the existence of multiple ionization and recombination sites, the high density and periodic structure makes for richer dynamics allowing the possibility of higher conversion efficiency. At present, it is safe to say that while HHG in atomic gases has been explored extensively, much less has been done for bulk crystals. Interestingly enough, NDABASHIMIYE G et al. reported a direct comparison of HHG in the solid and gas phases of Ar. They found that the HHG spectra of the noble gas solids exhibit multiple platforms, well beyond the atomic limits of the corresponding gas phase harmonics measured under similar conditions, implying that shorter attosecond pulses could be realized in solids. What is most interesting to us is that the dependence of HHG on the laser polarization direction with respect to the Ar crystal, which are currently little studied. We theoretically investigated optimal control of isolated attosecond pulse generation in an Ar crystal irradiated by few-cycle femtosecond pulse, employing quantum time-dependent density-functional theory method. We explored systematically the effect of different laser polarization directions on isolated attosecond pulses generation, showing that the laser polarization direction with respect to the crystal is a sensitive control parameter for producing isolated attosecond pulses. The results indicate that for an Ar crystal, the intensity of isolated attosecond pulses is maximal at an optimal laser polarization direction with respect to the crystal, demonstrating about 11-fold intensity enhancement compared with that generated in an Ar atom under the same driving laser pulses. Our results also suggest opportunities for future investigations for the optimal control of isolated attosecond pulse generation in bulk crystal solids.
Acta Photonica Sinica
- Publication Date: Oct. 25, 2022
- Vol. 51, Issue 10, 1032002 (2022)
All-optically Measuring Mechanical Parameters of Bio-surface/interface with Femtosecond Laser Spectroscopy（Invited）
He ZHANG, Wenxiong XU, Qiwei LI, Chuansheng XIA, Xiaoxuan WANG, Haibo DING, Chunxiang XU, and Qiannan CUI
The mechanical properties and parameters of bio-surface/interface are very important in fundamental researches and applications, such as constructing organ-on-a-chip in order to realize vitro culture of human cells and tissues. To acquire mechanical parameters of bio-surface/interface for real human cells, Atomic Force Microscopy (AFM) is usually employed. The young's modulus of human cells' surface/interface can be obtained by measuring the stress and strain of human cells induced by AFM tip. Obviously, this conventional method is invasive, which might not only cause damage of bio-surface/interface such as cell membrane, but also accompany a low speed for sensing and imaging applications. Besides, ultrasound elastography imaging has been developed to obtain three-dimensional distribution of mechanical parameters for bio-tissues. Unfortunately, the MHz ultrasound waves emitted by conventional ultrasound transducer limit its spatial resolution to micrometer. Hence, developing an accurate, in-situ, noninvasive and quantitative measuring method with high spatiotemporal resolutions to evaluate the mechanical performances has been highly desired. In recent years, layered Two-dimensional (2D) semiconductors, such as Transition Metal Dichalcogenides (TMDs) have presented extraordinary fundamental physical properties as well as good biocompatibility. Van der Waals bondings facilitate their facile integrations with other materials, including bio-materials, to form hetero-interfaces. Most importantly, previous studies have shown that GHz Coherent Acoustic Phonon (CAP) oscillations can be generated under femtosecond laser excitations. Although TMDs show great potential as novel optoacoustic transducers, the effective generation of CAP pulse and experimental measurements of mechanical parameters of bio-surface/interface still need further investigations.In this paper, employing layered 2D semiconductors as GHz optoacoustic transducer, we report a new all-optical technique to noninvasively, accurately, and swiftly measure mechanical parameters of bio-surface/interface based on femtosecond laser pump-probe. To demonstrate our technique, 2D optoacoustic transducer/bio-material hetero-interface formed by integrating multilayer MoS2 samples with PEGDA hydrogels are comprehensively investigated. Initially, through deformation potential mechanism, one femosecond pump pulse absorbed by multilayer MoS2 can induce GHz CAP oscillations, which is usually called interlayer breathing mode. Then, MoS2 lattice will periodically strike the surface of the PEGDA hydrogel and a CAP pulse can be emitted into PEGDA hydrogels by interfacial coupling of mechanical energy. Emitted CAP pulse will propagate in PEGDA at the speed of acoustic velocity. Since light speed is about five order of magnitude larger than acoustic velocity, to track the spatiotemproal propagations of emitted CAP pulse, another femtosecond probe pulse is employed. As the propagation of the emitted CAP pulse can induce a strain of PEDGA hydrogel, optical refractive index of PEGDA hydrogel will be changed so that by monitoring the differential reflection of probe laser as function of time delay with respect to the pump pulse, one can record the spatiotemporal propagation of emitted CAP pulse. As a result, the differential reflection signal of the probe laser contains exponential decay component originating from photocarrier relaxation of MoS2 and the damped oscillation components originating from CAP oscillation of MoS2 lattice as well as CAP pulse propagation in PEGDA hydrogel. To decouple the signal of CAP pulse propagation in PEGDA hydrogel, a curve fitting procedure is performed. At last, from frequency spectra obtained by fast Fourier transformations of the fitted time-resolved damped oscillation components, two different resonant frequency peaks are obtained. The higher resonant peak centered around 30.0 GHz is corresponding to CAP oscillations of MoS2 lattice, while the lower resonant peak below 10.0 GHz is caused by spatiotemporal propagation of the emitted CAP pulse in PEGDA hydrogel. Based on the model of Brillouin oscillation for CAP, mechanical parameters, such as acoustic velocity and Young's modulus of PEGDA hydrogel, are calculated. Last but not the least, we investigate five different positions of MoS2/PEGDA hydrogel interface. The spatial dependence of the mechanical properties of PEGDA hydrogel is discussed. In brief, physical principles, theoretical models, experimental systems, data analysis and calculation methods of the reported all-optical technique have been clearly demonstrated. Our results set a solid foundation for understanding CAP dynamics of hetero-interface, developing novel optoacoustic transducers for bio-surface/interface and realizing interfacial imaging of mechanical parameters with ultrahigh spatiotemporal resolutions. The mechanical properties and parameters of bio-surface/interface are very important in fundamental researches and applications, such as constructing organ-on-a-chip in order to realize vitro culture of human cells and tissues. To acquire mechanical parameters of bio-surface/interface for real human cells, Atomic Force Microscopy (AFM) is usually employed. The young's modulus of human cells' surface/interface can be obtained by measuring the stress and strain of human cells induced by AFM tip. Obviously, this conventional method is invasive, which might not only cause damage of bio-surface/interface such as cell membrane, but also accompany a low speed for sensing and imaging applications. Besides, ultrasound elastography imaging has been developed to obtain three-dimensional distribution of mechanical parameters for bio-tissues. Unfortunately, the MHz ultrasound waves emitted by conventional ultrasound transducer limit its spatial resolution to micrometer. Hence, developing an accurate, in-situ, noninvasive and quantitative measuring method with high spatiotemporal resolutions to evaluate the mechanical performances has been highly desired. In recent years, layered Two-dimensional (2D) semiconductors, such as Transition Metal Dichalcogenides (TMDs) have presented extraordinary fundamental physical properties as well as good biocompatibility. Van der Waals bondings facilitate their facile integrations with other materials, including bio-materials, to form hetero-interfaces. Most importantly, previous studies have shown that GHz Coherent Acoustic Phonon (CAP) oscillations can be generated under femtosecond laser excitations. Although TMDs show great potential as novel optoacoustic transducers, the effective generation of CAP pulse and experimental measurements of mechanical parameters of bio-surface/interface still need further investigations.In this paper, employing layered 2D semiconductors as GHz optoacoustic transducer, we report a new all-optical technique to noninvasively, accurately, and swiftly measure mechanical parameters of bio-surface/interface based on femtosecond laser pump-probe. To demonstrate our technique, 2D optoacoustic transducer/bio-material hetero-interface formed by integrating multilayer MoS2 samples with PEGDA hydrogels are comprehensively investigated. Initially, through deformation potential mechanism, one femosecond pump pulse absorbed by multilayer MoS2 can induce GHz CAP oscillations, which is usually called interlayer breathing mode. Then, MoS2 lattice will periodically strike the surface of the PEGDA hydrogel and a CAP pulse can be emitted into PEGDA hydrogels by interfacial coupling of mechanical energy. Emitted CAP pulse will propagate in PEGDA at the speed of acoustic velocity. Since light speed is about five order of magnitude larger than acoustic velocity, to track the spatiotemproal propagations of emitted CAP pulse, another femtosecond probe pulse is employed. As the propagation of the emitted CAP pulse can induce a strain of PEDGA hydrogel, optical refractive index of PEGDA hydrogel will be changed so that by monitoring the differential reflection of probe laser as function of time delay with respect to the pump pulse, one can record the spatiotemporal propagation of emitted CAP pulse. As a result, the differential reflection signal of the probe laser contains exponential decay component originating from photocarrier relaxation of MoS2 and the damped oscillation components originating from CAP oscillation of MoS2 lattice as well as CAP pulse propagation in PEGDA hydrogel. To decouple the signal of CAP pulse propagation in PEGDA hydrogel, a curve fitting procedure is performed. At last, from frequency spectra obtained by fast Fourier transformations of the fitted time-resolved damped oscillation components, two different resonant frequency peaks are obtained. The higher resonant peak centered around 30.0 GHz is corresponding to CAP oscillations of MoS2 lattice, while the lower resonant peak below 10.0 GHz is caused by spatiotemporal propagation of the emitted CAP pulse in PEGDA hydrogel. Based on the model of Brillouin oscillation for CAP, mechanical parameters, such as acoustic velocity and Young's modulus of PEGDA hydrogel, are calculated. Last but not the least, we investigate five different positions of MoS2/PEGDA hydrogel interface. The spatial dependence of the mechanical properties of PEGDA hydrogel is discussed. In brief, physical principles, theoretical models, experimental systems, data analysis and calculation methods of the reported all-optical technique have been clearly demonstrated. Our results set a solid foundation for understanding CAP dynamics of hetero-interface, developing novel optoacoustic transducers for bio-surface/interface and realizing interfacial imaging of mechanical parameters with ultrahigh spatiotemporal resolutions.
Acta Photonica Sinica
- Publication Date: Oct. 25, 2022
- Vol. 51, Issue 10, 1032001 (2022)
Research Progress of Attosecond Pulse Generation and Characterization （Invited）
Hushan WANG, Huabao CAO, Liangwen PI, Pei HUANG, Xianglin WANG, Peng XU, Hao YUAN, Xin LIU, Yishan WANG, Wei ZHAO, and Yuxi FU
Attosecond pulse light source， born at the turn of 21st centruy， is a fully coherent light source with attosecond-temporal and nano-spatial resolution， leading to the remarkable progress and breakthroughs in attosecond science in the past two decades. New research methods and important innovation opportunities in physics， chemistry， biology， materials， information and other fields have emerged with the advent of attoseond pulse. This review surveys the important efforts aimed at developing attosecond pulses， mainly summarizes the key technologies and status of high-order harmonics， attosecond pulse generation and attosecond pulse measurement， and presents the development prospects of attosecond pulse research in the end. Attosecond pulse light source， born at the turn of 21st centruy， is a fully coherent light source with attosecond-temporal and nano-spatial resolution， leading to the remarkable progress and breakthroughs in attosecond science in the past two decades. New research methods and important innovation opportunities in physics， chemistry， biology， materials， information and other fields have emerged with the advent of attoseond pulse. This review surveys the important efforts aimed at developing attosecond pulses， mainly summarizes the key technologies and status of high-order harmonics， attosecond pulse generation and attosecond pulse measurement， and presents the development prospects of attosecond pulse research in the end.
Acta Photonica Sinica
- Publication Date: Jan. 25, 2021
- Vol. 50, Issue 1, 1 (2021)
ALL-SOLID-STATE MULTI-WAVELENGTH FEMTOSECOND PULSE LASER SYSTEM
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Acta Photonica Sinica
- Publication Date: Jan. 01, 2002
- Vol. 31, Issue 9, 1112 (2002)
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