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Having different color components. This is different from the traditional laser.
Ultrafast laser has extremely high power and power density. At present, a laser system can even produce up to.
Peak power 1015w, while the average power of the world power grid is only10w. Such a high job
21112 10w/cm2 can create many extreme experimental environments, such as superlight field: superelectric field:10.
V/cm, super magnetic field: > 10 G, ultra-high acceleration: 10 g, ultra-high temperature: > 10 K, ultra-high pressure: > 10 Bar. This provides us with the possibility of studying physical phenomena under extreme conditions.
In recent years, the rapid development of miniaturized ultrafast laser technology has provided new experimental means and extreme physical conditions for human beings. This extreme physical condition created in the laboratory can only be found in the center of a nuclear explosion, inside a star or at the edge of a black hole. Under the condition that ultrafast laser technology has provided and will provide stronger and faster light fields due to its further development, the interaction between laser and various forms of matter will enter an unprecedented ultrafast intense field dominated by high nonlinearity and relativity, and the interaction between light and matter will be further studied to a deeper material level, even the interaction between light and vacuum, thus creating a brand-new frontier field of modern science and technology.
In recent ten years, due to chirped pulse amplification (CPA)
The proposal and application of ultrafast laser technology, the appearance of broadband laser crystal materials (such as titanium-doped sapphire) and the invention of Kerr lens mode-locking technology have made ultrafast laser technology develop rapidly. Miniaturized femtosecond terahertz (10W) or even higher ultrafast laser systems have been built and played an important role in laboratories all over the world. Recently, it has been reported that shorter pulse and higher power laser output, such as laser pulse shorter than 5 femtoseconds directly generated by laser oscillator, miniaturized femtosecond 100 MW ultrafast laser system, and CPA technology have been applied to traditional large-scale Nd: glass laser devices to obtain laser output of 1 picowatt (10 watt). The study on the interaction between ultrafast laser and matter with laser power density of10/9 ~1020919981215w/cm2 has also begun.
The traditional laser amplification adopts direct traveling wave amplification, but for ultrashort laser pulses, with the increase of energy,
With the increase, its peak power will increase rapidly, and various nonlinear effects and gain saturation effects will appear, thus limiting the further amplification of energy.
The principle of CPA technology is to broaden the pulse through dispersive elements while maintaining the same spectral width.
Several orders of magnitude, forming a so-called chirped pulse. Therefore, in the amplification process, even the energy of the laser pulse
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With the rapid increase of output, the peak power can also be maintained at a low level, thus avoiding the nonlinear effect and gain saturation effect and ensuring the stable growth of laser pulse energy. When the energy reaches the energy that can be obtained by saturation amplification, the peak power can be greatly improved by compressing the pulse to its original width with the help of the component opposite to dispersion when the pulse is broadened.
In order to break through some limitations of CPA technology, the international community is actively exploring and developing a new generation of super power supply.
The new principles and methods of ultrafast lasers such as chirped pulse optical parametric amplification (OPCPA) aim to create stronger and faster ultrafast extreme physical conditions, especially to obtain the focusable laser intensity greater than (equal to) 102 1W/cm2. OPCPA gives full play to the advantages of chirped pulse amplification and optical parametric amplification, and is a brand-new technical way to develop ultra-strong and ultra-fast lasers in recent years.
At present, the principle of OPCPA is still in the pre-research stage of medium power level, but it contains strong vitality.
Force. In addition, the optimization of ultrafast laser beam quality, the shaping and control of space-time profile, the generation of ultrashort laser pulses with periodic pulse width less than 10 femtosecond, effective amplification and performance optimization are also the main directions of sustainable innovation and development in the future.
Ultrafast laser technology plays an extremely important role in promoting the development of basic science and high technology. ultra-fast
Laser is not only of great significance in frontier disciplines, but also will create a brand-new laboratory scale, that is, the so-called desktop science and technology with comprehensive extreme conditions, thus directly promoting the development of laser science and a large number of basic disciplines such as modern optics, atomic and molecular physics, plasma physics, high-energy physics and nuclear physics, condensed matter physics, astrophysics, theoretical physics and nonlinear science, and in the innovative development of some important high-tech fields in contemporary times, Such as the new scientific principle of sub-femtosecond or even attosecond (65,438+)18 seconds, the new concept of rapid ignition in laser nuclear fusion, the new scheme of laser-induced desktop fusion neutron source, and the miniaturized ultra-high gradient particle accelerator.
The new mechanism and mode of ultra-short wavelength ultra-fast coherent radiation on the table also play an irreplaceable role.
At present, the ultra-high repetition rate has been produced on the desktop laser system which is much smaller than the traditional device.
Short pulse (usually 10- 13 seconds or even shorter) terawatt or even higher-order laser output. The focused laser intensity has increased by five or six orders of magnitude in the past decade, reaching1019 ~1020 w/cm2. Soon, it will reach the record of 102 1W/cm2, thus creating extreme physical conditions on a laboratory scale. Under the light intensity of 102w/cm2, the local electric field will be as high as 10 12v/cm, which is equivalent to 170 times of Coulomb field strength at the first Bohr orbit of hydrogen atom. The corresponding magnetic field will reach the super-strong range of 105 tex;
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The corresponding energy density has been above 3× 10 10J/cm3, which is equivalent to the energy density of a blackbody with a temperature of 10KeV. At the same time, it will produce huge light pressure, which is close to 10 17 Pa. In such a high laser field, the oscillation kinetic energy of electrons will be higher than 10 MeV (for laser with wavelength of 1.06 micron), which greatly exceeds the rest mass of electrons (0.5 MeV), and the acceleration of electrons will also reach 1022m/S2, that is,102/.
The early research in this field shows that the interaction between intense laser and atoms and molecules leads to new phenomena such as tunnel ionization, barrier suppression ionization, high-order odd harmonics, stabilization, molecular phase control and Coulomb explosion. The traditional perturbation method for nonlinear problems has been replaced by non-perturbation theory. At present, the interaction between ultrafast laser and atom has entered a new stage in which relativistic effect plays a leading role, so Dirac equation must be used to correctly handle the dynamic behavior of the interaction. On the other hand, the laser pulse width obtained today is less than 10 femtosecond, and the shortest is 4 femtoseconds, which only contains 1.5 optical periods (for lasers with a wavelength of 800 nanometers). Strictly speaking, the optical pulse at this time has not become a "light wave" and lost the unique periodic characteristics of fluctuation phenomenon. The traditional theory of interaction between light and matter with longer pulse width is no longer applicable, thus producing a new extremely nonlinear interaction theory. The interaction between ultra-intense ultra-fast laser with periodic or even sub-periodic pulses and various forms of matter will also lead to a series of new physical phenomena and laws. It is an urgent research task to seek these new phenomena and laws and establish related new concepts and theories, and it is also the focus of international competition in the field of ultra-strong and ultra-fast laser science.
The interaction between ultrafast laser and clusters, high temperature and high density plasma, free electrons and other special substances has also become a new research direction, which not only greatly broadens the in-depth development of this discipline, but also provides new schemes and new ways for the innovative development of related important high-tech fields.
Recently, it has been observed that multiphoton excitation produces a large number of "hollow" atoms with electron configuration inversion in the inner shell, which will open up a new way to realize ultrashort wave long wavelength radiation. The interaction between ultrafast laser and large-scale atomic clusters successfully triggered desktop fusion for the first time, which pointed out the prospect for the new concept of "desktop" fusion. In addition, the study of the interaction between ultrafast laser and clusters may serve as a bridge to help people understand the interaction between light and matter more comprehensively.
When the light intensity is greater than (equal to) 10 18 W/cm2, the interaction between laser and electron enters the super-relativistic strong field range. It is observed for the first time in the experiment that free electrons are accelerated to the relativistic energy of megaelectron volts in vacuum. Nonlinear Thomson scattering at about 300 femtoseconds and 0.05 nm and its ultrafast.
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Hard x-ray pulse; Multiphoton nonlinear Compton scattering. It is particularly striking that the strong field quantum electrodynamics phenomenon of inelastic photon-photon scattering producing positive and negative electron pairs is observed for the first time.
The generation and application of X-ray and γ-ray sources based on nonlinear Thomson scattering and Compton scattering, and the acceleration of electrons by ultrafast laser field with sub-periodic pulse width in vacuum are also hot topics in the study of the interaction between ultrafast laser and free electrons. In addition, the ultra-high gradient acceleration field is also observed in the wake field experiment produced by the interaction between ultra-fast laser and rare plasma, which is more than three orders of magnitude higher than the limit acceleration field of traditional high-energy particle accelerator, so a new scheme to realize the miniaturization of high-energy particle accelerator is proposed.
In recent years, the interaction between ultrafast laser and high-temperature and high-density plasma, especially the study of highly nonlinear new phenomena and laws caused by relativistic effect, has also attracted great attention from international academic circles. At present, it has been observed that the ultra-intense ultra-fast laser produces huge optical pressure, pushing the critical density surface forward, thus forming new phenomena such as plasma channels, but it involves the interaction between ultra-fast laser of the order of1018 ~1020 w/cm2 and high temperature and high density plasma, such as "hole-drilling" effect, generation of superheating electrons and energy spectrum. Obviously, the research on the interaction between ultrafast laser and high temperature and high density plasma is not only one of the important research contents in this field, but also may provide a basis for the development of related high-tech fields such as laser nuclear fusion.
The discovery and in-depth study of ultra-fast laser field excited high-order harmonics not only provides an effective way to obtain completely coherent light sources in vacuum ultraviolet region (VUV) and extreme ultraviolet region (XUV), but also provides a brand-new idea and method for the generation of sub-femtosecond or even attosecond ultra-fast short-wave long-wavelength radiation, thus it is possible to break through the femtosecond barrier and create ultra-fast attosecond photon technology, attosecond spectroscopy, attosecond physics and even attosecond for human beings.
A major breakthrough has been made in the research of high-order harmonic emission in ultrafast laser field, and high-order harmonics have entered the "water window" band. At present, the research on new concepts and methods of generating sub-femtosecond or even attosecond ultrafast coherent radiation is increasingly active. In the research of short-wavelength X-ray band laser, the existing X-ray laser mechanism can't achieve the breakthrough of wavelength less than 2 nm, and the appearance of ultrafast laser makes it possible to realize ultrashort wave long-wavelength radiation based on new mechanisms such as inner shell transition. At present, the research on the new mechanism of ultrashort wave radiation driven by ultrafast laser in the inner shell has also become a new hot spot in this field.
Ultrafast laser technology provides innovative means and methods for the development of interdisciplinary subjects. Ultrafast laser technology also provides innovative means and methods for the development of ultrafast chemical kinetics, microstructure materials science, ultrafast information photonics and life science. Such as ultrafast laser itself and its interaction with matter.
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Femtosecond may even be ultrafast coherent light source technology in sub-femtosecond, attosecond, XUV and X-ray bands, which provides a powerful means for human beings to study and apply various ultrafast processes, and will enable human beings to further understand the energy transfer and information transfer processes in micro-world materials at a deeper level, and then may realize the manual control of some physical, chemical and biological processes, promote the research and development in cross-disciplinary fields such as microstructure materials science and ultrafast chemical kinetics, and produce breakthrough cross-disciplinary research results with great influence.
In recent years, the research progress of femtosecond laser applied to chemical reaction kinetics has attracted much attention. Zevel won the 1999 Nobel Prize in chemistry for developing femtosecond spectroscopy technology and studying transition states with extremely short life in chemical reactions. The above progress also brings new hope for using ultra-fast and intense laser to control chemical reactions. Some small molecular chemical bonds have been successfully selectively broken or formed, but the complex system of macromolecules cannot be broken. The combination of ultra-fast intense laser technology and near-field optical microscopy technology can control the interaction between laser and molecules in many dimensions, which is a powerful means to study "single molecule physics" or "single molecule chemistry" and may be used to "cut" biological macromolecules.
Ultrafast intense laser has also made remarkable progress in the preparation of material microstructure and the study of ultrafast dynamic behavior, including the development and application of new detection methods with ultra-high spatio-temporal spectral resolution. For example, the optical pump-ultrafast X-ray diffraction probe measurement technology has been applied to the ultrafast lattice dynamics research of single crystals, achieving ultra-high temporal and spatial resolution of picoseconds-milliangstroms; Micro-explosion and micro-polymerization make it possible for people to obtain material processing accuracy better than diffraction limit and less than optical wavelength with ultra-fast intense laser, which brings new applications in three-dimensional high-density data storage. Recent experiments have also confirmed that the recording density can be increased to 1, 0 1.4 bit/cm ~ 3 by intermittently irradiating the glass with rare earth element samarium particles at micron intervals with multi-wavelength overlapping recording technology.
Relatively speaking, ultrafast laser science is a very young new discipline, which is on the eve of a major breakthrough, and its important role and potential far exceed that described in this paper. Looking forward to the 2 1 century, Chinese scientists are expected to make important achievements in the active frontier field of modern physics and even modern science. This is both a challenge and a rare opportunity.
(University of Science and Technology of China PB09206060)
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