High-power Laser Drivers Research Articles

Spatial-temporal modulation method of nanosecond laser for the double-cone ignition scheme.

In order to improve the stability of the pulse, realize the high requirements of the direct drive ignition design for the uniformity of the target irradiation, reduce the interference of laser plasma instability, and improve the laser-target coupling efficiency, a nanosecond laser spatial-temporal modulation of high-power laser driver for double-cone ignition (DCI) research was proposed. Under the premise of satisfying the near-isentropic compression waveform of driving implosion, the time-power curves of all sub-beams in the facility are redistributed to reduce the waveform contrast ratio of each sub-beam. A fewer number of sub-beams are utilized to generate low-power foot pulses, which are focused on the target surface of the initial radius. And the remaining sub-beams are utilized to generate high-power driving main pulses, which are focused on a relatively small target surface. It is shown that the stability of the time-power curve of each sub-beam and the power balance control ability can be effectively improved by redistributing. At the same time, the variable focal spot control can be realized to reduce the influence of cross-beam energy transfer (CBET).

Development of slurry targets for high repetition-rate x-ray free electron laser experiments

Combining an x-ray free electron laser with a high-power laser driver enables the study of equations-of-state, high strain-rate deformation processes, structural phase transitions, and transformation pathways as a function of pressure to hundreds of GPa along different thermodynamic compression paths. Future high repetition-rate laser operation will enable data to be accumulated at >1 Hz, which poses a number of experimental challenges, including the need to rapidly replenish the target. Here, we present a combined shock compression and an x-ray diffraction study on epoxy (50% vol.)-crystalline grains (50% vol.) slurry targets, which can be fashioned into extruded ribbons for high repetition-rate operation. For shock-loaded NaCl-slurry samples, we observe pressure, density, and temperature states within the embedded NaCl grains consistent with observations from shock-compressed single-crystal NaCl.

Preface

The 2021 International Conference on Sensing Technology and Applications (ICSTA 2021) was held on April 23-25, 2021 as a virtual conference due to the growing concerns over the coronavirus outbreak (COVID-19), and in order to protect the well-being of our attendees, partners, and staff as our number one priority. The meeting focused on the research fields of “Sensing Technology” and “Sensing Applications”. The aim is to provide a common forum for researchers, scientists, engineers and practitioners throughout the world to present their latest research findings, ideas, developments and applications in the area of sensing technology, to explore the development path of ecological civilization construction, and to cope with new opportunities and challenges.This scientific event brings together more than 50 national and international researchers in sensing technology and applications. On top of the local participants coming from different national universities, international participants are also registered from different countries, namely USA, Vietnam, India and Egypt. During the conference, the conference model was divided into three sessions, including oral presentations, keynote speeches, and online Q&A discussion. In the first part, some scholars, whose submissions were selected as the excellent papers, were given about 5-10 minutes to perform their oral presentations one by one. Then in the second part, keynote speakers were each allocated 30-45 minutes to hold their speeches.In the second part, we invited six professors as our keynote speakers. Prof. Bingguo Liu, from Harbin Institute of Technology, China, delivered a wonderful speech: On-line Vision Inspection technology for high-power laser drivers of inertial confinement fusion. And then we had Prof. Chengying Yang, from University of Taipei, Dept. of Computer Science. He shared a speech on his specialty related to Smartphone Based Tracking System Applied within the Classroom. Prof. Zhi Gao, from Wuhan University, China. His speech title was Vision for Intelligent systems and Intelligent Systems based Vision. In this talk, advanced techniques of these two aspects were introduced, including bio-inspired motion estimation, localization in challenging environments, and target detection. Prof. Yang Chai is an Associate Professor at the Hong Kong Polytechnic University. He shared a speech: Near-sensor and in-sensor computing for neuromorphic machine vision. Prof. Qingyang Wei, from University of Science and Technology, Beijing. He performed a thought-provoking speech: Lonizing Radiation Detection using CMOS Sensors. The last keynote speakers, Prof. Xinhua Tang, from Southeast University, Nanjing, China. He presented an insightful speech: Information fusion technologies inside GNSS-related navigation system. Their insightful speeches had triggered heated discussion in the third session of the conference. Every participant praised this conference for disseminating useful and insightful knowledge.The proceedings are a compilation of the accepted papers and represent an interesting outcome of the conference. Topics include but are not limited to the following areas: Sensing Theory and New Approach, Sensors and Actuators, Chemical & Bio Sensor System and more related topics. All the papers have been through rigorous review and process to meet the requirements of International publication standard.We would like to acknowledge all of those who supported ICSTA 2021. The help and contribution of each individual and institution was instrumental in the success of the conference. In particular, we would like to thank the organizing committee for its valuable inputs in shaping the conference program and reviewing the submitted papers.Committee of ICSTA 2021Committee member, General Conference Chair, Program committee, International technical committee are available in tha pdf

Development of low-coherence high-power laser drivers for inertial confinement fusion

The use of low-coherence light is expected to be one of the effective ways to suppress or even eliminate the laser–plasma instabilities that arise in attempts to achieve inertial confinement fusion. In this paper, a review of low-coherence high-power laser drivers and related key techniques is first presented. Work at typical low-coherence laser facilities, including Gekko XII, PHEBUS, Pharos III, and Kanal-2 is described. The many key techniques that are used in the research and development of low-coherence laser drivers are described and analyzed, including low-coherence source generation, amplification, harmonic conversion, and beam smoothing of low-coherence light. Then, recent progress achieved by our group in research on a broadband low-coherence laser driver is presented. During the development of our low-coherence high-power laser facility, we have proposed and implemented many key techniques for working with low-coherence light, including source generation, efficient amplification and propagation, harmonic conversion, beam smoothing, and precise beam control. Based on a series of technological breakthroughs, a kilojoule low-coherence laser driver named Kunwu with a coherence time of only 300 fs has been built, and the first round of physical experiments has been completed. This high-power laser facility provides not only a demonstration and verification platform for key techniques and system integration of a low-coherence laser driver, but also a new type of experimental platform for research into, for example, high-energy-density physics and, in particular, laser–plasma interactions.

高功率激光驱动器光束匀滑技术研究（特邀）

高功率激光驱动器光束匀滑技术研究（特邀）

高功率激光驱动器光束匀滑技术研究（特邀）

高功率激光驱动器光束匀滑技术研究（特邀）

Lasers for Novel Accelerators

Novel accelerator schemes are rapidly emerging in the wake of laser-plasma acceleration research and involve advanced high-power laser drivers for their operation. Significant progress has been made in laser performance during the past decade, including repetition rate, average and peak power, and footprint, making these systems attractive for many applications, including novel accelerators. Here we discuss laser driver requirements for the proposed novel accelerator schemes, examine emerging technologies and introduce a viable laser driver concept for a first generation of plasma accelerators.

Novel Quantum Beams from Integrated Laser-Driven Accelerator Systems

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Temporal pulse precisely sculpted millijoule-level fiber laser injection system for high-power laser driver.

A fiber laser injection system used as a seeder for a high-power laser facility of inertial confinement fusion was designed to meet stringent requirements. Herein, we demonstrate the fiber laser injection system, whose output single-pulse energy reaches the millijoule class. With two-stage amplitude modulators, the system produces a pulse with a higher pulse shaping capability. In addition, amplifying the pulse with large-mode-area fiber and single polarization, large-mode-area photonic crystal fiber (PCF) ensures a good beam quality output. In this proof-of-principle experiment, the long-term stability of FM-to-AM modulation and pulse energy is demonstrated. The successful demonstration of this laser injection system holds great significance for future high-power laser drivers.

高功率激光驱动器中幅频效应及其抑制技术研究进展

高功率激光驱动器中幅频效应及其抑制技术研究进展

Performance of smoothing by spectral dispersion with consideration of the gain characteristic of Nd:glass amplifier

A key issue in developing a high-power laser driver, which can be used for inertial confinement fusion and laser produced plasma experiments, is to obtain uniform irradiation on the target surface, thus a number of spatial or temporal techniques have been proposed for laser beam smoothing. A scheme combining a lens array with the technique of smoothing by spectral dispersion (SSD) is being explored in the SG-II Laser Facility located in Shanghai Institute of Optics and Fine Mechanics. As the laser system involves a variety of optical elements, their influences have to be considered in the implementation of such a scheme. The Nd:glass amplifier is one of the most important parts of the system, and the phase-modulated laser beam will propagate through it along the long light path when SSD is employed. In this paper, the performance of uniform irradiation of the target pattern is studied based on two-dimensional simulations when the gain characteristic of the amplifier is taken into account. The major factors, such as the small signal gain profile of the amplifier, the amplification factor, the bandwidth of the phase-modulated laser beam and the difference between the central wavelength of the laser and the central wavelength of the amplifier gain curve, are analyzed in detail. The numerical results show that when the central wavelength of the incident beam is different from the central wavelength of the amplifier gain curve, intensity distribution of the target pattern will be affected to a degree depending on the amplification factor; while these two wavelengths are very close to or identical with each other, variation in the intensity distribution is trivial. The symmetry of the phase-modulated laser spectrum will be destroyed due to the gain characteristic of the amplifier, especially when the bandwidth is relatively wide. However, the slight asymmetry does not result in significant influence on the spatial power spectrum nor uniformity of the target pattern, even in the case where the central wavelength of the incident beam is different from that of the amplifier gain curve. The reasons would be 1) the gain curve of the amplifier is actually quite flat within the laser bandwidth, and 2) with the technique of SSD, all spectral components contribute to the target intensity distribution within an average time. The analysis indicates that the performance of uniform irradiation of the target pattern depends mainly on the bandwidth of the phase-modulated laser beam. A wider bandwidth can always generate better irradiation when it is within a certain range, say no more than 0.3 nm, but beyond this range, the nonuniformity tends to remain at a level about 0.250.3. Multistage Nd:glass amplifiers will be employed in the practical laser driver, and the case investigated in this paper involves only one stage for simplicity. The conclusion obtained in this paper is important for implementing the technique of SSD in the laser system.

Light intensity distribution of high-power laser beams on target plane under different focus system of 22 beam array

Large aperture high-power laser drivers usually focus the high power laser beams in 22 quads to the target chamber center in order to increase the light intensity on the target plane. The large aperture wedged focus lenses are the core components in the focus system of quadruplets of beams, and it is thought possible to use four two-dimensional off-axis wedged focus lenses as four sub-lenses to make up a larger aperture wedged focus lens in form to focus the four beams. Given that the large aperture two-dimensional off-axis wedged focus lenses are processed and used difficultly, the wedged focus lenses are divided into three categories: the two-dimensional off-axis wedged focus lenses, the one-dimensional off-axis wedged focus lenses, and the non-off-axis wedged focus lenses. On the basis of the three modes of the wedged focus lenses and the corresponding specific incidence angles of each sub-beam, the three focus schemes for the 22 beam array are put forward to comparatively research the light intensity distribution on the target plane. Research results show that from a perspective of the coherence among the four sub-beams, the phase factors of each sub-beam respectively introducing by the three focus systems with the two-dimensional off-axis, one-dimensional off-axis, and non-off-axis wedged focus lenses are asymmetric, asymmetric and symmetric inside each sub-beam, and symmetric, asymmetric and symmetric among the four sub-beams. Therefore, the wave front consistency of the four sub-beams decreases in the order of the focus systems with the non-off-axis, two-dimensional off-axis, and one-dimensional off-axis wedged focus lenses. The focus schemes with the non-off-axis wedged focus lenses for 22 beam array can get the narrowest main-lobe, the strongest peak-value intensity, the highest energy concentration ratio on the target plane, followed by the one-dimensional off-axis and two-dimensional off-axis wedged focus lenses. The off-axis mode of the wedged focus lenses not only increases the complexity in the course of processing and using, but also increases the main-lobe size, decreases the peak-value intensity and the energy concentration ratio, which obtains a weaker focusing characteristics than that of the non-off-axis mode of the wedged focus lenses. Research results can provide an important reference for the design of the focus system in the target area of high-power laser drivers.

SG-II-Up prototype final optics assembly: optical damage and clean-gas control

The Shenguang-II Upgrade (SG-II Up) facility is an under-construction high-power laser driver with eight beams, 24 kJ energy, 3 ns pulse duration and ultraviolet laser output, in the Shanghai Institute of Optics and Fine Mechanics, China. The prototype design and experimental research of the prototype final optics assembly (FOA), which is one of the most important parts of the SG-II Up facility, have been completed on the ninth beam of the SG-II facility. Thirty-three shots were fired using 1- ${\it\omega}$ energy from 1000 to 4500 J and 3- ${\it\omega}$ energy from 500 to 2403 J with a 3 ns square pulse. During the experiments, emphasis was given to the process of optical damage and to the effects of clean-gas control. A numerical model of the FOA generated by the Integrated Computer Engineering and Manufacturing code for Computational Fluid Dynamics (ICEMCFD) demonstrated that a flux within $1{-}5~\text{l s}^{-1}$ and a 180 s period is effectual to avoid contaminant sputtering to the optics. The presence of surface ‘mooning’ damage and surface spots located outside the clear aperture are induced by contaminants such as wire, silica gel and millimeter order fiber and metal.

Beam guiding system geometric arrangement in the target area of high-power laser drivers

With the increasing number of laser beams, the main difficulty in arranging beam guiding systems (BGSs) involves determining the corresponding relationships between the output and input ports to realize the identified light path length of all beams. Given the basic constraints of geometric arrangement, a BGS model is established, and a base-line algorithm is proposed to address the difficulty mentioned above. Boundary conditions of target area and target chamber are discussed to increase the number of laser beams, and a maximum value exists for a specific target area. Finally, the compatibility of a cylindrical hohlraum target chamber with a spherical hohlraum is analyzed, and a moveable final optics assembly is proposed to execute the switch between the two different targets.

Cooperation Design of Target Area for ICF Facility Based on Top-Down Mode

The top-down mode has been widely used in the cooperation design of complex products. It has great advantages over traditional down-up mode for such a complex system as target area for the ICF facility. By taking target area of National Ignition Facility (NIF) for example, this paper will present a process of three-dimensional cooperation design supported by a design platform. The parametric design software Creo (upgraded Pro/E) and PDM software Windchill PDMlink are seamlessly connected in the platform using the floating license. The whole design process of target area was based on top-down mode and driven by the skeleton models. The sub-assembly includes target chamber, beam transport system, and supporting system. The design has been concurrently accomplished by the system engineer and the sub-assembly engineers on the design platform. It has validated the feasibility of the cooperation design based on the top-down mode. It can technically support the realization of the cooperation design for NIF scaled high-power laser driver.

Fast ignition with laser-driven proton and ion beams

Fusion fast ignition (FI) initiated by a laser-driven particle beam promises a path to high-yield and high-gain for inertial fusion energy. FI can readily leverage the proven capability of inertial confinement fusion (ICF) drivers, such as the National Ignition Facility, to assemble DT fusion fuel at the relevant high densities. FI provides a truly alternate route to ignition, independent of the difficulties with achieving the ignition hot spot in conventional ICF. FI by laser-driven ion beams provides attractive alternatives that sidestep the present difficulties with laser-driven electron-beam FI, while leveraging the extensive recent progress in generating ion beams with high-power density on existing laser facilities. Whichever the ion species, the ignition requirements are similar: delivering a power density ≈1022 W cm−3 (∼10 kJ in ≈20 ps within a volume of linear dimension ≈20 µm), to the DT fuel compressed to ∼400 g cm−3 with areal density ∼2 g cm−2. High-current, laser-driven beams of many ion species are promising candidates to deliver such high-power densities. The reason is that high energy, high-power laser drivers can deliver high-power fluxes that can efficiently make ion beams that are born neutralized in ∼fs–ps timescales, making them immune to the charge and current limits of conventional beams. In summary, we find that there are many possible paths to success with FI based on laser-driven ion beams. Although many ion species could be used for ignition, we concentrate here on either protons or C ions, which are technologically convenient species. We review the work to date on FI design studies with those species. We also review the tremendous recent progress in discovering, characterizing and developing many ion-acceleration mechanisms relevant to FI. We also summarize key recent technological advances and methods underwriting that progress. Based on the design studies and on the increased understanding of the physics of laser-driven ion acceleration, we provide laser and ion-generation laser-target design points based on several distinct ion-acceleration mechanisms.

高功率激光驱动器靶定位瞄准单元技术研究进展

高功率激光驱动器靶定位瞄准单元技术研究进展

高功率激光驱动器光束自动准直目标定位算法

高功率激光驱动器光束自动准直目标定位算法

兆焦耳级高功率激光驱动器光机结构设计

兆焦耳级高功率激光驱动器光机结构设计

Investigation on FM-to-AM conversation of the optical flat plates in complex laser systems

At present, in most high-power laser drivers the phase modulation is used to suppress the effect of stimulated Brillouin scattering and meet the requirement for target surface light intensity uniformity. However, the modulated pulses show intense FM-to-AM effect after transmitted through a complex laser system. Analyzing the source of this effect is essential to the improvement of the output performance of whole laser system. In this paper, the theoretical analysis and the numerical simulation of the FM-to-AM conversion of the optical flat plates are investigated, which has been ignored by many researchers. The simulation results show that the more the laser passes through the optical flat plates, the deeper the modulation will be (for example, the modulation depth will be as high as 22.2% when transmitting ten times), and it follows a linearly increasing trend. What's more, the different flat optical elements have different spectral filtering effects. When the central wavelength of the front-end is chosen to be 1054 nm, the spectral filtering effect is very weak. To our knowledge, the reduction of the FM-to-AM conversion by changing the central wavelength is presented for the first time.