After the appearance of laser, it entered the femtosecond (10–15s) ultra-fast era with the help of mode-locking technology, and was quickly applied to frontier basic scientific research such as physics, biology, chemistry and materials. Professor Zeval won the 1999 Nobel Prize in Chemistry for his pioneering research in femtosecond chemistry. Chirped pulse amplification technology (CPA) has further pushed the laser into the super-strong era [1], and related scientists have won the Nobel Prize in Physics for 20 18 years.
Ultra-fast and ultra-intense laser refers to a special light field with ultra-fast time domain characteristics and ultra-high peak power characteristics, which creates unprecedented extreme physical conditions such as ultra-fast time, ultra-high intensity field, ultra-high temperature and ultra-high pressure for human beings in the laboratory, and greatly promotes the development and progress of frontier science and interdisciplinary subjects such as physics, chemistry, biology, materials and medicine. It can be considered that ultra-fast and ultra-intense laser is one of the most important tools to expand the frontier basic scientific research of human cognition, and even a unique and irreplaceable research means in some aspects.
Ultra-fast and ultra-intense laser technology not only promotes the continuous expansion of cutting-edge basic scientific research, but also faces the new capacity support demand of cutting-edge basic scientific research because of its continuous deepening exploration, which gives strong traction to the development of laser technology system. In this paper, the development and scientific application requirements of ultra-fast and ultra-intense laser and the technical development at home and abroad are mainly combed, and on this basis, the development goals and key directions in this field in China are demonstrated and analyzed in order to provide direction reference for the steady development of laser technology in China.
Second, the application and development demand analysis of ultra-fast and ultra-intense laser.
The application and expansion of ultra-fast and ultra-intense laser in related frontier basic science research need to further improve laser parameters and explore other parameters of laser pulses, so as to push ultra-fast and ultra-intense frontier basic science research to a deeper material level. According to the different goals of cutting-edge scientific research, the future application and development needs of this field are concentrated in the following two parts.
(1) ultrafast laser and its scientific application
The future development demand of this direction can be subdivided into attosecond laser and even femtosecond laser, and ultra-fast ultraviolet-terahertz full-band femtosecond laser with accurate and controllable multi-dimensional parameters.
Attosecond laser and even femtosecond laser pursue ultrafast laser with shorter pulse width to study ultrafast process in matter, so it is necessary to develop high-performance attosecond (10–18s) laser with higher pulse energy, shorter pulse width and higher photon energy. The photon energy of attosecond pulse is pushed to the hard X-ray band and γ-ray band, and the pulse width is pushed to the second time scale (10–21s), thus pushing the material level that human beings can explore from the atomic/molecular level to the nuclear scale [2].
Femtosecond time scale corresponds to the ultrafast process of rich material systems, such as atoms/molecules, materials, biological protein, chemical reactions, etc., and has extensive and important applications. With the further development and deepening of research, it is necessary to explore richer and more complex ultrafast dynamic processes in order to control these ultrafast processes. In order to modulate and utilize the multi-dimensional parametric characteristics of ultrafast laser, it is necessary not only to extend the spectrum of femtosecond laser to infrared-terahertz band and vacuum ultraviolet-extreme ultraviolet band, but also to develop femtosecond ultrafast laser with precise control of multi-dimensional parameters including time domain, amplitude, phase, spectrum, polarization and spatial mode, represented by femtosecond ultrafast laser with precise control of multi-dimensional parameters in extreme ultraviolet-terahertz full band.
(2) Superintense laser and its scientific application.
According to different positioning and application targets, this direction can be divided into ultra-high peak power ultra-high laser with low repetition rate and ultra-high average power ultra-high laser with high repetition rate. Among them, the low repetition frequency means that the laser pulse repetition frequency is 10 Hz and below, and the high repetition frequency means that the laser pulse repetition frequency is 1 kHz and above.
Only by using ultra-strong laser can human beings create the unique extreme physical conditions inside the cosmic stars and nuclei in the laboratory. Using ultra-high peak power laser with low repetition rate, frontier physical problems such as laser particle acceleration, photonuclear physics and γ -ray collision can be studied. In the laboratory, we also study astrophysical phenomena, such as supernova explosion, solar flare, black hole accretion disk jet and so on. Macroscopically, we can also study the frontier basic sciences such as gravitational waves, dark matter, vacuum physics and so on. In order to meet the needs of important theoretical and experimental research in China, such as nuclear physics such as laser particle accelerator, nuclear transmutation, high-energy physics, new ways of laser fusion energy, laser nuclear medicine, etc., ultra-high peak power laser with low repetition rate provides an important scientific research tool.
In the application fields related to national strategic needs, such as aerospace safety, aerospace environmental physics, etc. The ultra-intense laser with high average power is an important driving tool, especially the ultra-intense laser with high repetition rate which can adapt to the special space environment. Ultra-intense laser with high repetition rate and high average power produces ultra-intense proton beam, electron beam, neutron beam, X-ray and γ-ray, which makes the secondary ultra-intense light source such as ultra-intense terahertz pulse as a new tool, which can be extended to more advanced major basic scientific research and practical applications such as photo-nuclear reaction, laser propulsion, nuclear fusion energy and nuclear waste treatment, and disease treatment.
Third, the research status of ultra-fast and ultra-intense laser at home and abroad
(1) ultrafast laser and its scientific application
1. attosecond ultrafast laser
The development of nearly 20 years shows that the fundamental limitation of the application of attosecond pulse broadband harmonic generation lies in the low single pulse energy, and the international mainstream solution is to establish a femtosecond ultrafast laser system with high power and long wavelength. The European Union invested hundreds of millions of euros to establish an extreme optical device-attosecond pulse source (ELI-ALPS) in Hungary, which generates attosecond pulses with high peak power and high average power through two petawatt laser systems [3]. Long-wavelength mid-infrared femtosecond laser pulse system can generate attosecond pulses with higher photon energy and shorter pulse width [4], so many research institutions are engaged in this work. The research of attosecond laser with high repetition rate has also made important progress [5]. In addition, the attosecond pulse generated by X-ray free electron laser (XFEL) has also been preliminarily verified. XFEL has certain advantages in generating high-power attosecond pulses with high photon energy (hard X-ray and γ-ray bands).
The domestic attosecond laser research is mainly concentrated in Shanghai Institute of Optics and Fine Mechanics, Shanghai Institute of Physics and Xi 'an Institute of Optics and Fine Mechanics, affiliated to China Academy of Sciences. Due to the late overall layout, the current research level is still relatively backward. In 2009, Shanghai Institute of Optics and Fine Mechanics measured the pulse width of attosecond pulse chain and obtained attosecond pulse laser near the limit of Fourier transform. In 20 13, a single attosecond pulse was generated and measured by the Institute of Physics, and a pulsed laser with a pulse width of 160 as was obtained. Xi Institute of Optics and Fine Mechanics has undertaken many tasks in the research of attosecond pulsed laser. Domestic institutions of higher learning, such as Huazhong University of Science and Technology, East China Normal University, Peking University and National University of Defense Technology, are also conducting attosecond laser research. In addition, some research institutions have also carried out a series of work in accelerating the generation of high-energy electrons and gamma rays by high-power lasers.
2. Femtosecond ultrafast laser
Using nonlinear optical method, the wavelength of femtosecond laser has been extended from visible-near infrared band to deep ultraviolet-ultraviolet and infrared-terahertz band internationally. Free electron laser has also obtained vacuum ultraviolet and extreme ultraviolet bands and terahertz ultrafast femtosecond lasers, which have the advantages of high energy and tunable wavelength, but the related devices are more complicated. In order to study more complex and rich ultrafast dynamic processes, multi-parameter light field precise regulation and multi-wavelength femtosecond ultrafast lasers have also been developed.
Many domestic research teams directly use commercially imported femtosecond lasers and superimpose nonlinear effects to expand parameters such as wavelength. Shanghai Institute of Optics and Mechanics, Shanghai University of Science and Technology, Xi Jiaotong University and other institutions have completed a series of research on precise control of light field and multi-wavelength femtosecond ultrafast laser. In 20 19, the free electron laser built by Dalian Institute of Chemistry, Chinese Academy of Sciences has been put into operation, and the ultrafast laser output with continuously adjustable wavelength has been realized in vacuum ultraviolet and extreme ultraviolet bands of 50~200 nm, which has supported and expanded the femtosecond ultrafast laser in basic scientific research [6]. China Academy of Engineering Physics has realized ultra-fast laser output in terahertz band by using free electron laser.
(2) Superintense laser and its scientific application.
The international research in this field is progressing rapidly and the competition is fierce. More than 50 sets of tile laser devices have been built in the world.
1. Ultra-high peak power laser with low repetition rate
The European Union, the United States, Japan, South Korea, Russia and other countries or regions are all building 10-watt laser major scientific devices. Recently, many countries or regions have put forward the development plan of 100~200 PW major laser scientific device. Nearly 40 scientific research institutions in EU 10 countries jointly put forward the Super Optical Infrastructure (ELI) project, aiming at developing 200 PW super laser devices, which has been included in the EU's roadmap for the future development of scientific instruments. In 20 19 years, the ultra-strong laser output of 10 PW was realized [8]. The French Apollon laser device [9] achieved 5 PW laser output in 20 17 years, and 10 PW laser output in 20 18 years. The higher index output is currently delayed. The UK Vulcan laser facility [10] plans to adopt optical parametric chirped pulse amplification (OPCPA) technology to increase the peak output power from gigawatt to ten gigawatt. XCELS is planned to be used for extreme optical research in Russia, with the goal of achieving a peak power of 200 PW. The laser device to be built includes 12 ultra-intense lasers with power of 15 PW and pulse width of 25 fs, and the laser is output by coherent combining technology [1 1]. Japan's Laser Fast Ignition Experiment Project (LFEX) has realized the output of petawatt laser with picosecond order and pulse energy of 2 kJ, which is mainly used to support the research of fast ignition laser nuclear fusion and astrophysics. Gwangju Institute of Science and Technology (GIST) in Korea has achieved a 4.2 PW laser output with a repetition rate of 0. 1 Hz based on the titanium gemstone CPA scheme. The OMEGA EP device of the University of Rochester in the United States has a laser output capacity of1kj/1PS/1pw, and the development idea of a 100-watt super laser is put forward simultaneously.
The research direction of ultra-high peak power laser with low repetition rate in China started earlier, and has formed a strong research team with reasonable echelon. Since 1996, 1 National Conference on High-field Laser Physics has been held every two years, which has significantly promoted academic exchanges and research progress in related fields. In recent years, China has made some important research achievements in this direction, some of which are already at the international leading level. In 20 17, the Chinese academy of engineering physics obtained a super-strong laser output of nearly 5 PW based on large-caliber lithium triborate (LBO) crystal and OPCPA technical route [13]. Shanghai Institute of Optics and Mechanics took the lead in achieving 5 PW laser output in the world in 20 16, and achieved 10 PW amplified output in 20 17 [14]. The laser output of 1 PW [15] is also realized by OPCPA technology. In 20 18, it was the first project in the world to start construction of100W ultra-strong laser device. In addition, some universities have recently put forward the planning idea of building dozens of tile-beating laser devices.
2. Super laser with high repetition rate and high average power.
The technical methods in this direction are mainly divided into disk ultrafast laser and fiber ultrafast laser. After solving the problem of thermal effect management of gain medium, the disk laser obtains an output with an average power of kW. Fiber femtosecond laser has the advantages of good heat dissipation, convenient and flexible integration, good beam quality and high conversion efficiency, and can realize laser amplification with repetition frequency above 1 MHz, which has developed rapidly in recent years. Limited by nonlinear effect, CPA output energy and power in optical fiber are not high.
In 20 12, Professor Mourou, an internationally renowned scholar, started the project "International Amplified Coherent Network" (ICAN) in the European Union [16], aiming at promoting the development of femtosecond laser based on optical fiber and its beam combining technology, realizing ultra-intense laser pulses with high repetition rate, high average power and high peak power, and exploring the driving source of a new generation of particle accelerators. Under the framework of ICAN project (10J/100fs/10 kHz ultra-intense laser), the University of Jena in Germany has led a number of researches on space-time beam combination of fiber femtosecond laser. For example, 16 fiber femtosecond lasers have been combined to obtain high repetition rate laser output with an average power of kW. The new technical scheme of combining spatial coherent beam combining (16 32) with temporal coherent beam combining or pulse superposition is expected to achieve 300 fs/ 100 TW ultra-intense laser output more economically [17].
There is still a lack of systematic research layout of ultra-intense laser with high repetition rate and high average power in China. Only a few scientific research institutes, such as Shanghai Institute of Optics and Mechanics, Peking University, National University of Defense Technology, and Tianjin University, have studied and explored the independent core technologies such as high-performance gain optical fiber development, disc laser amplification technology, optical fiber femtosecond oscillator, optical fiber CPA technology, space laser beam combining, pulse time accumulation and pulse compression. Some scientific research institutions and institutions of higher learning continue to study the technical direction of large mode area gain fiber, high energy and high power femtosecond laser and so on. In view of the good prospects in the field of micromachining, many domestic enterprises have developed fiber femtosecond laser products with power of tens of watts, and some enterprises have also introduced femtosecond ultra-fast laser products with power of 50 W and above. Despite the rapid development, most products need to use foreign key devices, and there are few key devices with independent intellectual property rights. Generally speaking, the research in this field is scattered, and the situation of systematic planning and division of labor and cooperation has not yet formed in the industrial chain.
Fourth, the development ideas and goals of ultra-fast and ultra-intense laser in China
(1) ultrafast laser and its scientific application
1. attosecond ultrafast laser
The photon energy of attosecond pulse breaks through to the level of 1 keV or even 10 keV, which supports the study of basic physical processes such as attosecond ultrafast inner shell electron dynamics and electron spin orbit dynamics, as well as the study of ultrafast electron dynamics and structural changes of complex structures such as macromolecules and even biomacromolecules. The key technologies involved include: high-power, short-period and stable carrier envelope phase mid-infrared laser system, high-brightness kiloelectron volt-attosecond laser pulse generation, high-resolution electron and multi-electron momentum measurement, and Compton scattering method to push photon energy to hard X-ray band and γ -ray band.
The pulse width of ultrafast pulse breaks through the second order, which supports the study of electron dynamics and even nuclear dynamics in deep inner shell. The photon energy of attosecond pulse reaches the level of 10 keV or even γ -ray band, and the attosecond pulse width may enter attosecond time scale. The key technologies involved include: technology related to improving power generation efficiency, ultra-fast measurement technology related to practical application, and one-second pulse width measurement.
2. Femtosecond ultrafast laser
With the development of basic scientific research on femtosecond ultrafast spectroscopy, apart from the time-domain characteristics of pulses, spectral and polarization characteristics are also important characteristics that can be utilized. The main research ideas are as follows: develop ultra-violet terahertz broadband femtosecond laser with megahertz repetition rate, develop high-performance, multi-wavelength femtosecond laser pulses and multi-wavelength femtosecond optical frequency combs, and realize the femtosecond laser with special space-time structure whose pulse shape and spatial radial polarization (or vortex) occur simultaneously and are precisely controlled; Develop ultra-fast lasers with gigahertz repetition rate, break through new ultra-fast spectral technologies such as single photon and quantum entanglement, improve the stability and detection efficiency of ultra-fast spectra, and support more pure microscopic systems and more complex multi-body ultra-fast dynamic process research; Using ultra-fast laser with multi-parameter precise control, the precise optical control of biological processes such as brain science, tumor, biological development and regeneration is studied.
(2) Superintense laser and its scientific application.
1. Ultra-high peak power laser with low repetition rate
Demand traction lies in studying major frontier physical science problems to expand human cognition. The future development direction is still to continue to improve the peak laser power (from 100 PW to 1 EW), seize the technical highland of the highest focusing power density (1025 W/cm2), and provide the most advanced extreme physical conditions for the frontier research of science. In order to improve the efficiency and reliability of this kind of frontier experiments, the repetition frequency of ultra-intense laser should be appropriately increased, and the ultra-intense laser output and its application research of special light fields such as vortex light should be carried out. The ultra-strong laser with precise control of space-time electric field and wavelength tuning will further expand its application range. With the continuous improvement of laser focusing power density, the time contrast of laser pulses is increasingly demanding, so innovative research on output and measurement is needed. In addition, the innovative research and design of large-aperture laser focusing has become an urgent need for development, which can effectively improve the focusing power density and alleviate the cost problems related to amplifying the output laser energy.
Peak power and repetition rate are the breakthrough points of future research and development. It is predicted that in 2025, 2030 and 2035, the laser output with peak power of 100 PW, 500 PW and 1000 PW( 1 EW) will be realized respectively, and the repetition frequency will also be improved. (1) It takes about 5 years to realize the single peak power output of 100 PW and the laser output with the repetition frequency of 10 PW; The laser device carries out vacuum polarization processing, supports basic research such as astrophysics and antimatter, and initially obtains breakthrough scientific research results. (2) About 10 year, by increasing the pump laser energy, the development and life extension of key components such as large-size gratings were broken through, and 500 PW laser output was realized by means of space laser beam combination, which supported the development of frontier major research such as gravitational waves and dark matter. ③ In the aspect of higher power pump laser, it takes about 15 years to realize the output of Ava-class laser by increasing the size and damage threshold of key devices such as large-size grating and combining with spatial coherent beam combining method; Develop a new focusing system to increase the focusing power density to1025 w/cm2; Explore new principles and methods to realize Ava-class laser output based on the interaction between light and matter, and open up new technical solutions for laser development; The ultra-intense laser reaching near quantum electrodynamics (QED) region is obtained, which supports the research of high-intensity laser physics.
2. Super laser with high repetition rate and high average power.
According to China's existing technical level, technical development expectation and the demand of major countries, the development of ultra-intense laser with high repetition rate and high average power has the following development trends. ① In about five years, we will focus on mastering the core technologies such as femtosecond fiber CPA, spatial coherent beam combining, pulse time accumulation and high-energy pulse compression, and reduce the complexity, difficulty and cost of this kind of laser through path and design innovation. ② It takes about 10 years to produce ultra-strong laser output with terahertz repetition rate in the laboratory; The attosecond laser pulses generated by high-field laser physics and laser electron acceleration are mainly studied, and the attosecond laser pulses of Qualcomm order are obtained, which promotes the development of attosecond dynamics research in atoms/molecules and materials. The breakthrough of laser technology will promote the great development of industrial applications and reduce the power cost of fiber femtosecond lasers. (3) It takes about 15 years to realize the ultra-strong laser output with repetition frequency above 10 TWKHz; Through the batch application in industrial field, the power cost of driving fiber femtosecond laser is significantly reduced; The space beam combination of terahertz laser is carried out, and the 10 terahertz laser with high repetition rate is realized in the laboratory; Focus on the research of miniaturized particle accelerators to promote the expansion and application of proton beams with high repetition rate and high energy in the medical field; The application of laser fusion energy and nuclear waste treatment is explored by using the high-energy neutron source generated by laser.
Five, the key technical direction of ultra-fast and ultra-strong laser.
1. attosecond ultrafast laser
The key development directions in the future mainly include: high energy single attosecond laser pulse, high average power attosecond laser, high photon energy attosecond pulse and miniaturized attosecond pulse with high repetition rate. The development direction of related technologies is: high-quality short-period (including mid-infrared) laser pulse technology, simple attosecond laser pulse measurement technology, new attosecond laser application technology, high-quality high-brightness hard X-ray and gamma-ray generation technology, millisecond laser technology.
2. Femtosecond ultrafast laser
The key development directions in the future mainly include: multi-wavelength high-performance femtosecond laser technology, broadband dual-frequency/multi-frequency comb femtosecond laser technology, megahertz high-repetition high-performance vacuum ultraviolet-extreme ultraviolet, infrared-terahertz ultrafast laser technology, femtosecond laser technology with special polarization and spatial mode such as radial polarization and vortex, gigahertz high-repetition miniaturized quantum dot ultrafast laser technology and vertical cavity surface emission (VCSEL) ultrafast laser technology, which involves time domain, spectrum, polarization and so on.
3. Ultra-high peak power laser with low repetition rate
Focusing power density and contrast are the most important parameters, and amplification technology, pulse compression technology, spatial focusing technology, contrast enhancement and measurement technology should be further developed. The key technical directions in the future specifically include: Qualcomm amplification technology (that is, ultra-high energy CPA or OPCPA technology and the development of corresponding ultra-large aperture laser crystals or nonlinear crystals), new amplification technologies such as plasma Raman amplification and quasi-parametric chirped pulse amplification (QPCPA), design and development of new compressors for large aperture and high damage threshold compression gratings, and large aperture and ultra-strong laser beam combining technology. Laser pulse contrast enhancement and single measurement technology, on-line measurement technology of space-time characteristics of large-aperture ultra-intense laser, wavefront shaping of large-aperture ultra-intense laser and design of new high-performance focusing system, precise control of space-time electric field and wavelength tuning technology of ultra-intense laser, pulse compression technology of ultra-intense laser pulse outside cavity, generation and application of ultra-intense laser with special light fields such as vortex and radial polarization, etc.
4. Super laser with high repetition rate and high average power.
The key development directions in the future mainly include: new femtosecond fiber amplification, new disc laser amplification technology, high repetition rate femtosecond laser pulse time accumulation and spatial coherent beam combining technology and its derivative innovation technology, phase measurement and active feedback control technology of multi-beam laser in spatial coherent beam combining, special fiber design and processing technology of new femtosecond laser amplification, pulse compression and dispersion management technology, high repetition rate laser pumping source technology, Thermal effect management technology in the process of high repetition rate amplification, development of core devices such as high performance gain fiber, high performance chirped fiber grating and transmission grating, precise control of spatio-temporal light field and wavelength tuning technology.
Countermeasures and suggestions on intransitive verbs
(3) Basic scientific research to improve human cognition requires not only the innovation and creation of domestic researchers, but also the intelligence and wisdom of global scientists. Strengthen international exchanges and cooperation, attract international talents to carry out joint research, and further accelerate and upgrade relevant scientific research. In the field of ultra-intense laser, which is already in the leading position in China, and some research directions with leading and subversive innovation, we can consider building major basic scientific devices under the framework of "Belt and Road", focusing on China and attracting other countries (such as Asian countries and Russian) to carry out joint research and technical research. Enhance the international influence of China's scientific and technological innovation through the sharing of basic scientific research achievements (similar to ELI Project and Black Hole Exploration Project).
(4) In order to better and faster realize the goal that basic research results serve the national economy and social development, it is suggested that scientific research institutions and institutions of higher learning should strengthen cooperation with enterprises and promote the efficient transformation of practical scientific and technological achievements of ultra-fast and ultra-intense laser. At the same time, strengthen the protection and management of intellectual property rights and do a good job in preventing technical risks.