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Two breakthroughs in the development of China's high-power solid-state laser technology

Two breakthroughs in the development of China's high-power solid-state laser technology

1. Introduction
Soon after the advent of lasers in 1960, famous scientists such as Academician Basov of the former Soviet Union, Nuckolls of the United States and Professor Wang Ganchang of China were keenly aware of the ability to create extremely high power density lasers in the laboratory, generate high temperature and high pressure conditions, induce nuclear fusion, and independently promoted early laser fusion research in their respective countries. Today, laser-driven inertial confinemeut fusion (ICF) research has become a major frontier scientific and technological field, which is the irreplaceable main technical way to study ICF and high energy density science (HEDs) in the laboratory, and is one of the main technical ways to create sustainable energy for mankind in the future.

The basic physical characteristics of ICF fusion ignition are the use of high-power-density energy to heat the combustion target, so that it is highly compressed to achieve self-sustaining combustion of the fuel, so as to achieve the conditions of thermonuclear ignition, the so-called "Lawson criterion". High-power lasers have significant advantages as ICF driving conditions, but it is not easy to achieve the precise conditions required by Lawson's criterion in the millimeter space and nanosecond time domain scale in the laboratory. First of all, it is required to drive the laser pulse with high enough energy and power, and also to have high beam quality, including laser wavelength, high beam quality, high target accuracy, accurate pulse waveform and synchronization accuracy. These technical requirements not only point out the direction for the research and development of high-power laser technology, but also pose great challenges to the development of high-power solid-state laser devices.

In the 70s of the last century, Professor Yu Min of the China Academy of Engineering Physics proposed that laser inertial confinement fusion is a very complex scientific project, involving five aspects of research content such as theory, experiment, diagnosis, target making and laser driver, and the coordinated development between each other, that is, the development idea of "five-in-one".

At present, the overall level of ICF research and giant laser drivers has become a reflection of a country's comprehensive national strength, representing the overall level of a country in the field of fusion science and high energy density scientific research. At present, the research of high-power laser technology has gone through a glorious development process, the first generation of technology has become history, the second generation of technology has become the mainstream of development, and the third generation of technology has emerged, indicating the vigorous vitality of the development of high-power solid-state laser technology.

Since the 70s of the last century, the United States, China, Britain, France, Japan, Russia and other countries have successively built a number of neodymium glass laser devices with nanosecond pulse width, with energy ranging from 100 joules to tens of kilojoules. In the 90s, developed countries began to build larger-scale devices, and the development of high-power laser technology entered a new historical period. In the mid-90s, the Livermore Laboratory (LLNL) in the United States took the lead in launching a large-scale scientific project with a total investment of billions of dollars and a ten-year period on the basis of the comprehensive development of a new generation of solid-state laser optical materials, unit technology and advanced overall design technology, and the construction of the National Ignition Facility (NIF). The French Atomic Energy Commission (CEA) began construction of a megajoule laser unit (LMJ) on a similar scale to NIF, and Russia plans to launch the world's most powerful laser system, UFL-2M, by the end of 2017, which will be used for research in the fields of high-energy-density physics and energy.

Ultra-high ultra-intense short-pulse lasers are another important direction of high-power solid-state laser technology. The Chirped Pulse Amplification (CPA) technology developed in the mid-80s is a new milestone in laser technology, and the ultra-strong ultra-short pulse laser technology has quickly become a hot spot of attention of various scientific and technological powers under the traction of fusion fast ignition and many interdisciplinary frontier disciplines and national defense applications.

2 Development history of high-power solid-state laser devices

In 1964, Professor Wang Ganchang, then vice president of the Chinese Academy of Materials, put forward the "proposal of using high-energy and high-power optical masers to generate neutrons", which was positively responded to by Deng Ximing and other scientists engaged in high-power laser technology research at the Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences (hereinafter referred to as the Shanghai Institute of Optics and Mechanics), as well as the support of Zhang Jinfu, the leader of the Chinese Academy of Sciences. Since then, China's high-power laser technology has a clear development direction, Shanghai Institute of Optics and Mechanics is the earliest research base, with the strong support of the institute, the Chinese Academy of Materials has gradually become a research base for high-power laser technology.

Both China and the United States began research on high-power laser drivers for ICF in the 60s, as shown in Figure 1, and in 1973, both countries have successfully developed laser drivers that can be used for ICF technology research. Unfortunately, in the past 10 years, the international laser technology and plasma physics have made continuous innovations and major breakthroughs, and many reasons have made China's research work lose an important development period, the United States built the Argus device in the late 70s, the larger Shiva device in 1978, the larger Nova device in 1982, and China only began the pre-research work of large-scale laser devices in the early 80s. At this time, China's high-power laser technology has lagged behind the United States a lot.

    

Despite the great difficulties in the development process, under the guidance of the older generation of scientists, the two research teams of the Shanghai Institute of Optics and Mechanics and the Chinese Academy of Materials have worked together to develop a number of solid-state laser devices for China, mainly including the Starlight series and Shenguang series laser devices. The two types of devices have different positions in ICF research, so they have formed a complementary ICF research pattern in China, which has promoted the healthy development of ICF research in China. The Starlight series laser device is mainly used for basic experiments, and at the same time of carrying out decomposition experiments and physical diagnostic equipment assessment and calibration, a number of new laser technologies have been developed in advance, such as triple frequency technology. Shenguang series laser devices are mainly used for comprehensive experiments, and the Shenguang-I and Shenguang-II devices mainly built by Shanghai Institute of Optics and Mechanics have played an important role in promoting the technological development of ICF in China.

The scale and performance of the Shenguang-I device, which was completed in 1986, are comparable in scale and performance to the Argus device in the United States, marking that China has basically mastered the key technology of the first generation of high-power laser drivers, and has become the first high-power laser device in China to serve the basic experimental research of ICF. In order to give full play to the role of the device and the advantages of the two units, the Chinese Academy of Materials and the Chinese Academy of Sciences decided to establish a "Joint Laboratory of High Power Laser Physics" in 1986. To this end, the Chinese Academy of Physics sent scientific researchers to Jiading, Shanghai, and established a laser laboratory, which is now the Shanghai Laser Plasma Research Institute of the Chinese Academy of Materials. The Chinese Academy of Materials has carried out a series of physical experiments on this device, and has achieved gratifying results, and at the same time, it has also trained and grown the team engaged in laser fusion research in China. In 1994, the Shenguang-I laser unit was decommissioned. The Shenguang-I device has been in continuous operation for 8 years, and has achieved a series of world-class physical achievements in cutting-edge fields such as ICF and X-ray laser.

In 2001, the Shenguang-II laser device jointly invested and developed by the Chinese Academy of Materials and the Chinese Academy of Sciences was put into operation. The power of the device is about 4 times higher than that of Shenguang-I, with 8 laser beams and triple frequency target capability. Since the completion of the construction of the Shenguang-II laser facility, a large number of high-level and high-energy-density physics experiments have been carried out, and a number of high-level physics experimental results with high precision and good repeatability have been obtained. The improvement of experimental conditions, marked by the completion of the Shenguang-II laser device, has brought ICF experimental research into a new period, marking the transformation of China's research in this area from basic research and capability development as the main goal to applied basic research as the main goal, and driving the development of capabilities. To this day, the device still plays an important role in the fields of high-energy-density physics, energy, and astrophysics.

3 Two "breakthroughs" in the research and development of China's high-power solid-state laser technology

The Chinese Academy of Physics has also developed a number of laser devices, as shown in Figure 2. According to the characteristics of laser technology, these devices can be divided into high-power laser technology represented by Starlight-I, Starlight-II, Shenguang-III prototype and Shenguang-III laser devices and ultra-short and ultra-strong laser technology represented by SILEX-I and Starlight-III laser devices.

        

3.1 Breakthrough in the new generation of high-power neodymium glass laser technology

In order to further improve the efficiency of ICF basic experimental research and cultivate a technical team for the future development of high-power laser technology, with the help of the Shanghai Institute of Optics and Mechanics, the Chinese Academy of Materials successfully developed a slightly smaller Starlight series device in the late 80s. In the 90s, the Chinese Academy of Materials reviewed the situation and launched the concept research and pre-research of the advanced key technology of a new generation of high-power laser device (i.e., Shenguang-III laser device) with multi-range amplification as the basic technical feature.

3.1.1 Starlight-I laser device

At the end of 1977, Professor Wang Ganchang led the relevant leaders and technical personnel of the Chinese Academy of Optics and Mechanics to the Shanghai Institute of Optics and Mechanics to discuss cooperation matters, and preliminarily planned that the two sides would invest in the development of a 1012W (2×800 J) laser device LF-12 (later known as Shenguang-I laser device) in the Shanghai Institute of Optics and Mechanics. In order to carry out physical experimental research and cultivate the laser team of the Chinese Academy of Physics as soon as possible, it was determined that the Shanghai Institute of Optics and Mechanics would develop a single-channel laser device LF-11 (later known as the Starlight-I laser device) with an output power of 1011W for the Chinese Academy of Materials. In 1983, the Chinese Academy of Physics sent several technicians to study at the Shanghai Institute of Optics and Mechanics, forming the core force of the operation, maintenance and improvement of the Starlight-I laser device, and giving birth to a young scientific and technological team engaged in high-power laser technology in the Chinese Institute of Physics.

The Starlight-I laser device was installed at the former site of the Institute of Nuclear Physics and Chemistry of the Chinese Academy of Materials, located in the deep mountains, and was completed and accepted in 1985. The Starlight-I laser device has an output beam diameter of 70 mm and a maximum output energy of 70 J. Prof. Wang Ganchang visited the Starlight-I Laser Device Laboratory, as shown in Figure 3.

   

Driven by physical requirements, the Starlight-I laser device has completed a number of domestic initiatives, mainly including:
(1) In order to meet the requirements of indirect drive physics experiments, the first cavity target small hole aiming and positioning system in China (1986) was developed, which solved the technical problems of precise laser beam guidance and focusing, realized the goal of high-precision and high-efficiency laser beam perforation, and laid the foundation for laser target shooting in ICF indirect drive physics experiments in China.
(2) In order to meet the requirements of the development of ICF physics experiments in China, the first practical high-power neodymium glass laser high-efficiency large-diameter KDP crystal (Ф70 mm) double-frequency system was developed in China (1987), with a double-frequency efficiency of 70%, which was close to the international advanced level at that time, and filled the gap in the application of large-diameter and high-efficiency double-frequency in China. The breakthrough of large-diameter and high-efficiency harmonic conversion technology has laid the foundation for high-efficiency harmonic conversion of subsequent large-scale laser devices in China.

(3) Large aspect ratio laser line focusing is one of the key technologies to realize laser pumped X-ray laser light, in order to solve this technical problem, an aspheric combined line focusing optical system was designed, and large aspect ratio line focusing (30 mm×50 μm) (1988) was realized, which made China the second country in the world to realize laser pumped X-ray laser (108.9 nm) after the United States two months later, and laid the foundation for China's X-ray laser experimental line focusing technology.

(4) Using the main laser beam splitting and spatial optical path delay, the stimulated Brillouin scattering technique was used to produce a probe laser with zero jitter synchronization accuracy, and the images of the disintegration process of the black cavity target at different times were obtained for the first time in China (1987), which preliminarily verified the scientific feasibility of the black cavity target experiment, see Figure 4.

     

3.1.2 Starlight-II laser device

In the early 90s, the Chinese Institute of Materials moved to Mianyang. At the same time, according to the new requirements of ICF physical experiments, the Starlight-I laser device was upgraded to the Starlight-II laser device in 1995. Since the Starlight-II laser device needs to have the ability to use basic experiments and decomposition experiments such as ICF, X-ray laser (XRL) and atomic parameters, as well as high-power laser technology research, in the process of designing and developing the Starlight-II laser device, the laser energy index of the device is not simply pursued, but the purpose is to improve the comprehensive performance index and operation efficiency of the device. At the same time, based on the mature laser unit technology in China, some advanced technologies are adopted to pursue the advanced nature of the device under the premise of ensuring the reliable and stable operation of the device. The main technical features of the Starlight-II laser device include:
(1) The device adopts active mode-locking-Q-switched technology and negative feedback control single longitudinal mode technology, and realizes the segmented adjustment of the output pulse width of the device in the range of sub-nanoseconds to nanoseconds.
(2) The polarization mismatch (Type II/Type II) triple frequency scheme and the structure of frequency doubling and mixing crystals packaged in the same frequency doubling box are used to realize the efficient conversion of the second and triple frequency lasers, and the maximum external conversion efficiency of the triple frequency is 65%, and the triple frequency technology level has reached the international advanced level; It has successfully solved technical problems such as three-wavelength separation, target targeting and positioning, and completed the physical experiment of triple frequency laser targeting for the first time in China.

(3) The shooting range adopts a double-target chamber structure, which effectively improves the operation efficiency of the whole device. Among them, a new target aiming and positioning system was established in the No. 1 target room, which realized the aiming and positioning of different wavelength laser targets with a collimated light source, and the target accuracy reached ±25 μm.
The main technical indicators of the Starlight-II laser device are as follows: the final output aperture is 180 mm, the device can output three wavelengths, namely 1.053 μm (fundamental frequency), 0.527 μm (double frequency) and 0.351 μm (triple frequency), pulse width 0.2-0.9 ns and 1.5-5 ns, maximum output energy of 260 J/1.053 μm and 130 J/0.351 μm, and the beam can be focused to 7-10 times the diffraction limit. At that time, it was the only high-power ultraviolet (laser wavelength of 0.351 μm) laser device suitable for laser fusion plasma experimental research in China. Figure 5 is a general overview of the Starlight-II laser device.

      

For the first time in China, the Xingguang-II laser device carried out the interaction experiment between the triple frequency laser and the planar target and the black cavity target, and obtained the experimental data of target absorption efficiency, X-ray conversion efficiency and cleanliness of the source area. For the first time in China, the single-line neon-like titanium-like X-ray laser gain experiment and the neon-like zinc-like light output experiment were completed, which opened up a precedent for small and medium-sized high-power solid-state laser devices to carry out X-ray laser experimental research.
3.1.3 Shenguang-II prototype device
In the early nineties of the last century, the state approved laser-driven inertial confinement fusion (ICF) as an integral part of the national high-tech development plan, and ICF research officially rose to the national level, receiving stable and long-term national support, and China's ICF entered a stage of rapid development. At the same time, the United States and France have accelerated the pace of research and development of giant laser devices in order to achieve the scientific goal of fusion ignition in the laboratory as soon as possible, and to actively cope with the difficult situation of physical research on nuclear weapons after the ban on nuclear weapons.
As the supporting unit of the ICF high-tech development plan, the Chinese Academy of Materials launched the conceptual research and advanced key technology research of the Shenguang-III laser device in a timely manner, and the development of the Shenguang-III prototype device was launched. It has successively developed a series of key technologies of a new generation of units, and developed high-power optical components (devices) such as large-size and high-performance neodymium glass, pulsed xenon lamps, KDP crystals, etc., especially large-diameter precision optical processing, coating, clean control, testing, assembly technology and engineering capabilities have been greatly improved.

The development of the Shenguang-III prototype device was officially launched in 2000. As the main body responsible for the implementation of the project, the Laser Fusion Research Center of the Chinese Academy of Materials has achieved the first beam of light in 2003, the first beam reached the standard in 2005, and was fully completed and passed the national acceptance in 2007, realizing a breakthrough in the research and development of a new generation of high-power laser devices in China.
A general overview of the Shenguang-III prototype device is shown in Figure 6. The Shenguang-III prototype device adopts the overall technical route of "four-range amplification" and "square beam, combined aperture, and array structure" as the main characteristics, and develops and innovates according to the specific situation of China, and the overall design integrates the advanced technology and successful experience of related fields or industries, and realizes the leap from the first generation technology to the second generation technology. The main performance parameters are 8 lasers with a diameter of 29 cm × 29 cm, and the output energy of each beam is 1.2 kJ to 1.8 kJ when the triple frequency wavelength and pulse duration are 1 ns-3 ns.

       

During the development of the Shenguang-III prototype device, it independently solved a series of scientific and technological problems and created a number of domestic "firsts", which are mainly manifested in the following aspects:
(1) Using key technologies such as asymmetric variable aperture beam transmission, beam angle rotation isolation and beam rotation compensation, and through the optimal combination of systems, a four-way amplification system with certain characteristics and good gain characteristics has been successfully developed, making China one of the few countries in the world that has mastered multi-range amplification technology.
(2) The research method combining theory and benchmark experiment is used to solve the key theoretical problems of the multi-range amplification system, and the key criterion of system design, the B-integral criterion, is accurately given.
(3) The technical route of "continuous phase plate shaping and spectral dispersion and smoothing" is adopted to realize the precise control of the light intensity of the target surface, and the output performance of the device beam uniformity and smoothing has reached the international advanced level.
(4) Using the technology of "single pulse and parallel drive", the high-performance, multi-unit plasma electrode electro-optical switching system has been successfully developed, making China the second country in the world to master this core technology.

(5) The fully cured and all-fiber front-end system successfully developed based on the "high-speed electronics to realize pulse time shaping technology" provides a stable and reliable laser seed light source for the device, and solves the problems of flexible beam splitting, precision synchronization and flexible layout of optical paths, making China the second country in the world to systematically master this key technology.
(6) For the first time in the world, the technology of "beam space shaping based on the modulation principle of liquid crystal light valve" was successfully adopted, and the active control of the near-field distribution of the output beam of the device was realized.
(7) Adopting the technical route of "pre-ionization + capacitance grounding", a new modular energy module with good electromagnetic compatibility, high energy storage density and high degree of automatic control has been successfully developed, and the overall technical level and performance of the module are close to the international advanced level.
(8) The terminal optical components integrating high-efficiency third harmonic conversion, high-precision focusing, high-precision diffraction sampling and measurement have been successfully developed, which provides extremely valuable experience for further improving the overall load capacity of the device.
(9) For the first time in China, the technology of "multi-beam spatiotemporal coding parallel guidance + target conjugate direct diagnosis" was adopted to realize the fast and accurate guidance of multi-beam lasers in the shooting range system and the precise positioning of the target in the benchmark physical experiment.

(10) For the first time in China, the centralized command, control and management of the whole device and the whole process of high-power laser driver have been realized.
(11) The whole process of production, processing and coating of 300 mm square diameter KDP crystal materials has been realized, and the 300 mm square diameter KDP crystal basically meets the basic requirements of the engineering development of key units such as electro-optical switches and terminal optical components of prototype devices, and its main performance indicators are close to the international advanced level.
(12) For the first time in China, a 300 mm square-aperture beam sampling element (BSG) with "imaging exposure + ion etching" as the main process was successfully developed, and the precision sampling of high-energy tripod laser pulse energy measurement was realized.
As the main driver of China's ICF research during the "Eleventh Five-Year Plan" and "Twelfth Five-Year Plan" period, the Shenguang-III prototype device carried out a series of physical experiments. By the end of 2015, the Shenguang-III prototype device had provided more than 2,000 effective target shots, with a target success rate of more than 90%. Considerable progress has been made in various physical experiments based on high-power solid-state laser devices.
The successful development of the Shenguang-III prototype device embodies the research results of China in the field of high-power laser driver for more than ten years, achieves the scientific and task objectives of device development, enables China to have a platform and necessary technical means for basic research in the field of high energy density science, and promotes the development of physical diagnosis and target technology. At the same time, the transformation of China's high-power laser driver science, technology and engineering research from "tracking and imitation" to "local innovation" has been realized, and the overall construction level of China's high-power laser driver has been upgraded. In addition, the construction of the device has also promoted the construction of China's high-power laser driver development system, cultivated and exercised the team of scientific and technological research, engineering implementation and management, and formed a new generation of high-power laser driver comprehensive design and construction capabilities.

3.1.4 Shenguang-III laser device

The Shenguang-III laser device is an important facility for the study of important physical processes before fusion ignition, which can lay the foundation for the development of larger-scale drivers, and focus on solving the engineering and large-scale problems of the construction of larger-energy laser drivers.
On February 4, 2007, the foundation stone of the Shenguang-III laser device laboratory was laid at the Laser Fusion Research Center of the Chinese Academy of Materials. The transparent aperture of the Shenguang-III laser device is increased to 40 cm×40 cm, and is composed of 48 laser beams, with a pulse width of 3-5 ns and a three-fold wavelength, which can output about 180 kJ of energy. This is the third largest laser device under construction in the world after the NIF in the United States and the LMJ device in France, and it is also the largest optical project in China's history.
At the end of 2011, the first beam was emitted, and in 2013, the number of beams reached 32. In September 2015, the Shenguang-III laser device was completed, and the device achieved a test output of 48 beams of 180 kJ/3 ns and a peak power of 60 TW for the first time. The scale and output capacity of the device are currently the second in the world and the first in Asia, and the high-power solid-state laser device with advanced performance indicators is a landmark facility in the development of China's optical engineering field. A general overview of the Shenguang-III device is shown in Figure 7.

      

From 2013 to 2015, the Shenguang-III laser device successfully completed several rounds of physical experiments, with a total of 465 shots. Important progress has been made in various comprehensive experiments. At present, the device has formed an average daily target shooting capacity of 2 rounds, and with the continuous deepening of the overall run-in of the device, the operation efficiency has shown a rapid upward trend.
The successful operation of the Shenguang-III laser device not only greatly improved the research capability of China's high-energy-density physics, but also embodied the "five major advances" of China's high-power solid-state laser technology and engineering:
(1) The system has mastered the overall design methods and technologies of giant high-power solid-state laser devices with "three physical foundations (pumping and amplification dynamics, transmission dynamics and damage dynamics), three design stages (feasibility study, preliminary design and engineering design), four design baselines (output capacity, beam quality, precise control and three-sex control), and six types of design elements (optical, mechanical, electrical, control, measurement and installation)" as the main characteristics, and realized the systematization and standardization of overall design and verification.
(2) The system has mastered the overall integration method and technology of the giant high-power solid-state laser device with the main characteristics of "three stages (processing and manufacturing, installation integration and online commissioning), three types of baseline (installation accuracy line, environmental clean line and integrated efficiency line), three types of verification (engineering design compliance, processing and manufacturing matching and engineering implementation guarantee), and three types of evaluation (integration evaluation, performance evaluation and operation evaluation)", and basically realized the process and standardization of batch installation and integration.
(3) The basic structure of the giant high-power solid-state laser device is realized by using the grouping technology, which is "component standardization, unit modularization, system array, and device integration", and a "modular" structural framework and performance index system covering five levels: overall, system, component (part), unit/module, and optical element (device) are constructed.

(4) The system has mastered the key technologies and processes such as the design, verification, manufacturing, installation and commissioning of the three main structures of the giant high-power solid-state laser device (laser hall beam group, target marshalling station and vacuum target chamber), and realized clean control and "high tower" stable support structure represented by the vacuum target chamber with a diameter of 6 m.
(5) Breakthrough or mastery of a number of key technologies (high-precision "seed light source", pre-amplification of high-quality laser beams, precision synchronization, radiation calibration damage detection, full-optical path precision wavefront correction, automatic collimation of many beam optical paths, automatic target targeting and positioning, computer centralized control, high-efficiency harmonic conversion, precision control of target light intensity, "one stranding" precision installation, ultra-precision optical processing, etc.), and successfully applied to the Shenguang-III laser device, the function is basically realized, and the performance is significantly improved.
(6) The development of the Shenguang-III laser device condenses China's top technological achievements in laser technology, optical engineering, pulse power, precision machinery, fast electronics, automatic control, chemical cleaning, advanced optical manufacturing and other disciplines, marking China's systematic development and capabilities in the overall design, overall integration, key technology, processing and manufacturing, optical detection, clean cleaning, precision assembly, support and other core capabilities of giant laser drivers, and is oriented to a larger scale The optical engineering system developed by ICF laser driver has been basically formed. For a long time in the future, the Shenguang-III laser device will become the core platform for ICF physics experimental research in China.

3.2 Breakthrough in ultra-strong ultra-short pulse laser technology
Since the invention of lasers, high peak power has been one of the scientific goals pursued in the development of high-power laser technology. In the mid-to-late 80s of the last century, the invention of chirped pulse amplification (CPA) technology promoted the leapfrog development of ultra-strong ultrashort pulse laser technology.
From the perspective of technical characteristics and application background, there are two technical approaches to the development of high-power ultrashort pulse laser technology, namely the picosecond high-energy type with neodymium glass as the amplification medium and the femtosecond high-power type with titanium-gem as the amplification medium, which can output laser pulses from hundreds of terawatts to petawatts, and the focusing power density reaches 1021-1022 W/cm2, which can produce extreme physical conditions similar to those inside the star and during the explosion in the laboratory. Some important areas of the national economy and people's livelihood have provided unprecedented research platforms and technical means. In the past 10 years, developed countries in the world have invested in the construction of a number of ultra-strong and ultra-short pulse laser devices. In order to improve the ability of scientific research and innovation and core competitiveness, the Chinese Academy of Materials has also carried out research on ultra-short and ultra-strong laser technology in a timely manner.
3.2.1 SILEX-I laser device
After three years of hard work, the Laser Fusion Research Center of the Chinese Academy of Materials built China's first 300 TW/30 fs titanium-sapphire laser device SILEX-I in early 2004, and its comprehensive technical indicators and performance reached the international leading level at that time. After its completion, it has been providing operational targets for high-energy density physics research, and is one of the few femtosecond laser devices in the world that can operate stably at that time, attracting dozens of domestic and foreign counterparts to cooperate in experimental research, and has achieved a number of research results with high academic value. The SILEX-I laser setup is shown in Figure 8.

      

3.2.2 Starlight-III laser device
On the basis of breaking through the overall and key technologies of 100 joule high-energy picosecond laser and completing the comprehensive verification, the upgrade of the starlight device was carried out based on the basis of the Starlight-II device and the SILEX-I device. That is, the petawatt-level femtosecond laser beam was obtained based on the SILEX-I ultrashort pulse laser device, and the petawatt-level picosecond laser beam and the kilojoule-scale nanosecond laser beam were obtained based on the 2×1 combined aperture multi-range amplification integrated experimental platform. In 2013, using the original "zero jitter" technology, the world's first "zero jitter" synchronous output of nanosecond, picosecond and femtosecond pulse widths, 527 nm, 1053 nm and 800 nm three wavelength lasers, and with multi-combination, multi-angle flexible targeting capabilities of multi-function strong radiation source laser device - Starlight-III laser device. A general overview of the Starlight-III laser installation is shown in Figure 9.

      

The three lasers output by the Starlight-III laser device at the same time can be used as the driving source and probe light for each other, and have the characteristics of mutual orthogonal and multi-angle and multi-combination targeting. In the process of device construction, the Chinese Academy of Materials has broken through and solved a number of technical problems, and has reached the international advanced level in short-pulse focal spot control technology, grating splicing and compression technology, etc., and the key technical indicators such as focusing on power density are comparable to those of international in-service devices.
The Starlight-III laser device has been put into operation for high-energy-density physics experiments and will be open to domestic and foreign countries. At present, the Starlight-III laser device has provided hundreds of rounds for more than 20 types of physical experiments, obtained 1.45 GeV single-energy electron beam output, laser proton acceleration energy reached 20 MeV for proton photography, and the laser neutron source achieved 5×108 single-shot output, etc. These research results, which are at the leading domestic and international advanced level, strongly support the relevant high energy density physics research. The completion of the construction of this device has significantly improved the level and status of China in the field of ultra-high power and ultrashort pulse laser technology, and will create a good experimental platform for the world's high energy density physics research.

4 Development trend of high-power solid-state laser technology

Looking at the achievements of the research and development of high-power solid-state laser devices over the past decades and the traction of future needs, a generation of high-power solid-state laser technology has become history; The second-generation high-power laser technology is thriving and has become the mainstream technology approach; Three generations of high-power laser technology have emerged and shown strong vitality.

(1) The first generation of high-power solid-state laser technology: with the basic research of ICF as the main traction goal, the most basic technical feature of the laser device is the use of "main oscillator + power amplification" (MOPA) technology route, with the basic characteristics of circular beam, single aperture and separation, and low energy conversion efficiency. The first generation of technology is represented by the Nova unit built in 1984 by LLNL in the United States.

(2) The second-generation high-power solid-state laser technology: the main traction goal is to realize laser fusion ignition under laboratory conditions, and the output energy of the laser device reaches millions of joules and the power reaches hundreds of terawatts. The second-generation technology is represented by the NIF of the American LLNL.

(3) The third generation of high-power solid-state laser technology: focusing on the needs of "post-ignition", it represents the development direction of high-power solid-state laser devices in the longer term, mainly including high energy density science (HEDs) research and laser fusion energy (LIFE) development. The laser device for HEDs is based on chirped pulse amplification technology or parametric amplification technology, which pushes the peak power of laser pulses from the current order of hundreds of petawatts to the order of 1018 watts. The laser device for LIFE should achieve high efficiency (the overall energy conversion efficiency of the device has been increased from less than 1% to more than 10%), high repetition frequency (the emission period has been increased from the current hours to sub-second level), high beam quality (several new technologies have been developed to achieve comprehensive control of beam space, time domain, frequency domain, and polarization) and high reliability.

5 Concluding remarks
Over the past decades, the laser fusion research of the Chinese Academy of Materials has made gratifying progress and has occupied an important position in the world. The R&D team of high-power solid-state laser technology and devices of the Chinese Academy of Materials has become the backbone of China's million-joule laser devices, achieving the ability to "keep pace" with the international advanced level, and at the same time driving the development of domestic high-power laser materials, optical processing, pulse power technology and precision machining industries.
Today, the Chinese Academy of Materials has ushered in a new historical opportunity for the development of laser fusion, and ICF research has formed a three-legged trend of the United States, China and Europe, and has become one of the important symbols of China's comprehensive national strength and core competitiveness.
Taking history as a mirror, we should not only look forward, but also learn and summarize the past, that is, under the traction of ICF and HEDs demand, fully absorb the successful experience and lessons of previous device development, take the active device as the carrier, through inheritance and innovation, continuously assess and verify the output capacity, beam quality, control ability and "three characteristics" (reliability, availability and maintenance) of the device, and at the same time improve the installation and integration accuracy and efficiency of giant laser devices, and consolidate the technology and engineering foundation of China's million-joule laser devices.

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Attenuation and shrinking beam simulation for beam quality measurement of high-power lasers

Attenuation and shrinking beam simulation for beam quality measurement of high-power lasers

fangyun DAI @

Beam quality factor is the main parameter to characterize the transverse pattern of high-power lasers, and in order to solve the problem that the current beam quality analyzer can only be used for beam quality evaluation of small-aperture and low-power lasers, the principle and simulation of attenuation and beam reduction technology for beam quality measurement of high-power lasers were studied. The simulation model of the attenuation and shrinking beam component is established, and the thermally induced aberrations of optical components under high-power laser are studied by using the finite element method, and it is concluded that when the peak-to-trough (PV) value of thermally induced aberrations is less than 82 nm, the influence on the beam quality factor is less than 5%. As the beam passes through the attenuation component, if debias occurs, the beam quality factor will be smaller. Based on the Zenic polynomial and the beam quality factor calculation model, the influence of the wavefront distortion of the beam shrinking component on the measurement is studied and analyzed, and it is seen through the Zemax simulation analysis that the influence on the beam quality factor measurement is less than 5% when the angle of view between the incident light and the center optical axis of the beam shrinking component is less than 7° during the assembly and adjustment.
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Depth: Research progress of high-power semiconductor lasers

Depth: Research progress of high-power semiconductor lasers

HighPowerLaser @

Laser is another major invention of mankind since the 20th century, after atomic energy, electronic computers, and semiconductors. Semiconductor laser science and technology takes semiconductor laser devices as the core, covering the study of the law, generation method, device technology, control means and application technology of stimulated radiation amplification of light, and the required knowledge integrates geometric optics, physical optics, semiconductor electronics, thermodynamics and other disciplines.

After more than 50 years of development, semiconductor laser, as a world-class research direction, has developed by leaps and bounds along with international scientific and technological progress, and has also benefited from breakthroughs in various related technologies, materials and processes. The progress of semiconductor laser has received great attention and attention in the international scope, not only in the field of basic science and continuous research and deepening, the level of science and technology continues to improve, but also in the field of application continues to expand and innovate, the application of technology and equipment emerge in an endless stream, the application level has also been greatly improved, in the national economic development of all countries in the world, especially in the fields of information, industry, medical and national defense has been an important application.

At present, the development of semiconductor lasers in the world is in a new stage of rapid development, and China's laser science and technology has basically maintained a trend of synchronous development with the world. From the perspective of comprehensive social development, industrial economic upgrading, national defense and security application and economic structure transformation, from the perspective of national competitive development, more clear needs are put forward for the comprehensive innovation of semiconductor laser technology and the transformation and development of industrial applications. In this paper, the development history and current situation of semiconductor lasers are reviewed, and the achievements of Changchun Institute of Optics, Fine Mechanics and Physics in recent years in high-power semiconductor lasers, especially in high-power semiconductor laser laser light sources, vertical cavity surface-emitting lasers and new laser chips.

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