WO2015139636A1 - 激光尾波场加速器及产生高亮度阿秒光脉冲的方法 - Google Patents

激光尾波场加速器及产生高亮度阿秒光脉冲的方法 Download PDF

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WO2015139636A1
WO2015139636A1 PCT/CN2015/074515 CN2015074515W WO2015139636A1 WO 2015139636 A1 WO2015139636 A1 WO 2015139636A1 CN 2015074515 W CN2015074515 W CN 2015074515W WO 2015139636 A1 WO2015139636 A1 WO 2015139636A1
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laser
gas
gas target
driving
wake field
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PCT/CN2015/074515
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French (fr)
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黎飞宇
盛政明
陈民
於陆勒
张�杰
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上海交通大学
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H15/00—Methods or devices for acceleration of charged particles not otherwise provided for, e.g. wakefield accelerators

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  • the invention relates to an accelerator and a coherent radiation source generating device, in particular to an ultrashort intense laser driven gas target, and a laser tail wave field accelerator for generating high brightness attosecond light pulses.
  • the more mature methods for generating ultrashort X-ray pulses are based on synchrotron radiation devices and free electron lasers of conventional accelerators, such as Shanghai Light Source, LCLS of SLAC, and the like.
  • advanced X-ray free electron lasers XFEL
  • XFEL advanced X-ray free electron lasers
  • the peak brightness of the optical pulse output by XFEL is 7 to 9 orders of magnitude higher than that of the synchrotron radiation source, which greatly broadens its application potential.
  • the United States "Science" magazine selected the top ten progress of the year including the use of X-ray laser (1 billion times brighter than the synchrotron source) to confirm the hook of an enzyme required by Trypanosoma brucei (this parasitic Insects are responsible for African sleeping sickness, which first proves the potential of coherent X-rays to directly decipher proteins.
  • the above-mentioned conventional accelerator-based radiation source devices are large in scale (several kilometers of acceleration distance) and expensive (about $1 billion per XFEL), thus limiting the application to a wider range of basic scientific and industrial applications.
  • Directly providing coherent radiation sources with low cost, high brightness and short pulse width is still one of the goals of future accelerators and radiation sources.
  • the traditional accelerator field is currently exploring whether it can generate X-ray pulses of attosecond pulse width.
  • the plasma can carry an effective accelerating electric field of up to 10 11 to 10 12 volts per meter, which is 3 to 4 orders of magnitude higher than that of a conventional accelerator.
  • a laser tail wave field formed by a strong laser-driven gas target can accelerate electrons at a distance of 3 cm. Up to 10 9 electron volts, laser plasma acceleration is considered to be one of the hot candidates for future compact, inexpensive high-efficiency accelerators.
  • ultrashort X/gamma ray pulses such as spontaneous synchrotron radiation of an electron beam in a wake acceleration structure, or Thomson/Compton with other laser beams. Backscattering.
  • These high-brightness sources have been used in applications such as single-shot imaging.
  • the poor controllability of electron injection in the wake field acceleration is usually quasi-continuously generated within a certain period of time, and the generated electron beam pulse width is hardly lower than the femtosecond magnitude. Therefore, the radiation source generated based on these electron beams is also often Femtosecond pulse width, non-coherent. A new breakthrough is needed to obtain the coherent radiation of the attosecond pulse width by accelerating the laser wake field.
  • a femtosecond laser with a light intensity of 10 14 to 10 16 watts per square centimeter can effectively excite high-order harmonic radiation of gas atoms, which in the frequency domain appears as an integer multiple of the incident light and appears as a period in the time domain.
  • Sexual attosecond pulse chain The method is based on a laser atomic process, and the incident light intensity requirement is less than 10 16 watts per square centimeter, so that the intensity of the generated attosecond pulse is not high.
  • relativistic intensity (>10 18 watts per square centimeter) of ultrashort lasers can produce high-intensity surface harmonics with solid targets. If these harmonic radiations are further high-pass filtered, a single attosecond pulse can be obtained. However, the harmonic intensity of the solid surface generally decreases rapidly with increasing harmonics, so the efficiency of filtering to produce a single attosecond pulse is not high.
  • various schemes have been proposed that can directly generate high-brightness coherent attosecond pulses. However, this solution requires extremely high laser contrast and is extremely difficult to experiment.
  • these solid target-based solutions are also not conducive to high repetition rate operation, and have great limitations in practical applications.
  • the new type of radiation source based on the interaction between strong laser and plasma has many unique advantages compared with the traditional accelerator-based scheme.
  • the program will provide low-cost, convenient high-quality attosecond light sources for a wide range of basic science applications, and will also break through the bottleneck of current ultra-short radiation sources based on traditional accelerators.
  • a laser wake field acceleration for generating an attosecond light pulse
  • the laser wake field accelerator includes: a laser source for generating a driving laser; and a vacuum chamber having a gas generating device and a focusing system in the vacuum chamber, wherein the gas generating device is configured to generate the laser along the driving laser A gas target having a rising density front is directed, and a focusing system is used to focus the drive laser.
  • the laser light generated by the laser source is focused by the focusing system, and the gas target is incident on the gas target, so that the gas molecules in the gas target are ionized by the laser beam, and the attosecond electron chip is injected and the electronic chip is synchronously accelerated, thereby obtaining an atomic pulse.
  • the above density includes the total electron number density.
  • the gas target having a rising density front is followed by a platform type or a descending density distribution.
  • transitions between the different density distributions are smoothed by an intermediate density platform.
  • the gas generating device comprises a gas nozzle which is a sub-millimeter long ultrashort supersonic gas nozzle, and the outlet of the gas nozzle has a sharp boundary.
  • the vacuum edge of the gas target ejected by the sub-millimeter ultra-short supersonic gas nozzle has a vacuum edge to a gas density platform of no more than 200 microns.
  • the outlet of the gas nozzle is rectangular or circular.
  • a metal piece for controlling the ejection form of the gas target is provided at the outlet of the gas nozzle, the metal piece having a sharp boundary, and the sharp boundary of the metal piece is in contact with the gas target.
  • the nozzle outlet direction is vertically upward, and the metal sheet is placed horizontally at the outlet of the gas nozzle, and the area of the shielding outlet is not more than 1/2 of the entire outlet area.
  • the metal sheet plane is held parallel to the nozzle exit plane by a support.
  • the laser wake field accelerator further includes a laser pre-processing system for providing a processing laser to the gas target for density distribution shaping of the gas target, the laser pre-processing system comprising: spatial light emphasis a mask sheet, a spatial light-emphasizing mask sheet for modulating a transverse spatial light intensity distribution of the processing laser, the single-hole line width of the mask sheet being 20-500 ⁇ m, preferably 50-200 ⁇ m; and a prism a prism pair for focusing the modulated processing laser and adjusting an absolute intensity of the processing laser; wherein the focused laser beam is incident on the gas target in a direction perpendicular to a propagation direction of the driving laser; and driving The laser is incident on the gas target later than the processing laser, and the delay of the driving laser to the gas target relative to the processing laser is not less than 2 nanoseconds, preferably the delay is 2-10 nanoseconds.
  • a laser pre-processing system for providing a processing laser to the gas target for density distribution shaping of the gas target, the laser pre-processing
  • the laser pulses generated by the laser source are split by a beam splitter to obtain a driving laser and a processing laser.
  • the spectroscopic transmittance of the spectroscope is greater than 9:1, and the laser light from the laser source is driven by the laser beam transmitted by the spectroscope, and the laser light from the laser source is reflected by the spectroscope.
  • the processing laser is one or more low energy beamlets.
  • the laser wake field accelerator further includes a full mirror for directing the drive laser and/or processing the laser.
  • the processing laser incident on the gas target covers the entire gas target or the front end of the gas target, and the front end refers to the end at which the laser and the gas target are first applied.
  • the above driving laser satisfies the following parameters:
  • the radius of the lumbar spot on which the laser is focused onto the gas target is on the order of microns, typically from 10 to 100 microns, preferably from 10 to 50 microns;
  • (b) driving the laser has a pulse width of 1 to 100 femtoseconds, preferably 5 to 50 femtoseconds;
  • the peak power of the driving laser is 100 to 10,000 terawatts, preferably 200 to 5,000 terawatts.
  • the driving laser is a fundamental mode Gaussian beam or a super Gaussian beam
  • the gas target is composed of a single gas or a plurality of gases having a low atomic number, preferably hydrogen, helium or a mixture thereof;
  • the gas target described above satisfies the following parameters:
  • the size of the gas target in the direction of driving the laser light is from 100 to 10,000 micrometers, preferably from 100 to 1000 micrometers;
  • the gas target has a uniform density uniformity within a certain dimension in a direction perpendicular to the direction in which the laser is driven, preferably the scale ranges from 10 to 100 microns;
  • the maximum electron number density of the gas target after ionization is from 10 18 to 10 21 per cubic centimeter, preferably from 10 19 to 10 20 per cubic centimeter;
  • the length of the rising density front along the direction of the driving laser propagation is 10 to 500 ⁇ m, preferably 50 to 200 ⁇ m.
  • the distance between the boundary of the ascending density front and the boundary of the highest density region in the direction of laser propagation is less than 10 times the wavelength of the electron plasma wave corresponding to the highest density (about 200 ⁇ m). ).
  • the rising density front includes a low density region (density between 0-0.25 n 0 ), a medium density region (density between 0.25 and n 0 ), and a highest density region (density n 0 ). ), where n 0 is the highest density.
  • the ascending density front has a minimum density of 0 and a maximum density of no more than 2 x 10 20 per cubic centimeter.
  • the rise is a linear rise or a linear rise.
  • the radius of the waist spot on which the driving laser is focused onto the gas target is greater than the wavelength of the electron plasma wave corresponding to the maximum electron number density of the gas target.
  • the laser wake field accelerator produces a dense electron flyer of attosecond pulse width, i.e., an electron beam in a sheet-like structure.
  • the attosecond optical pulse generated by the laser wake field accelerator has the following characteristics:
  • the cone angle ⁇ 0 with respect to the driving laser propagation direction is generally 10-30 degrees depending on the driving laser and gas target parameters;
  • a method for generating an attosecond light pulse comprising:
  • the invention is based on the principle that an ultrashort intense laser driven gas target generates a wake wave field to accelerate electrons, and proposes a new wake excitation and controllable electron beam injection mode to realize an attosecond pulse width and dense electron flyer (ie Injection of a sheet-like structure electron beam).
  • the injected electron flyer is accelerated in the wake field to produce a high intensity, coherent attosecond pulse.
  • the invention has the advantages of low technical requirements, high radiation quality and low cost, and is advantageous for providing a compact and high quality atomic radiation source for a wide range of basic scientific and industrial applications.
  • FIG. 1 is a schematic structural view of a laser wake field accelerator according to a first embodiment of the present invention
  • FIG. 2a is a schematic view showing the working principle of generating an attosecond light pulse of the present invention
  • Figure 2b is a possible form of the total electron number density distribution after ionization of the gas target required by the present invention
  • FIG. 3 is a schematic structural view of a laser wake field accelerator according to a second embodiment of the present invention.
  • FIG. 4 is a schematic structural view of a laser wake field accelerator according to a third embodiment of the present invention.
  • Figure 5 is a view showing a typical simulation result of an attosecond pulse generated by a laser wake field accelerator in an embodiment of the present invention
  • Figure 6 shows a typical spatial structure of the attosecond pulse generated along the center of the pulse in an embodiment of the present invention.
  • the inventors have conducted extensive and intensive research to propose a device which is relatively simple in structure but can efficiently generate high-brightness coherent attosecond light pulses. With this device, high-intensity attosecond light pulses can be generated conveniently and efficiently.
  • the present invention has been completed on this basis.
  • the present invention provides an apparatus and method for controlling the electron beam injection position by shaping a density distribution of a gas target, thereby realizing injection and acceleration of an attosecond pulse width electron beam in a wake wave field;
  • the electron beam wavelength is larger than the laser lumbar spot incidence condition, and thus the injected electron beam is a sheet-like structure having a large aspect ratio; the generated electron beam of the atto-pulse-width sheet-like structure is accelerated while being accelerated in the wake field.
  • the contraction motion is exerted by the action of the electrostatic field force, thereby generating a coherent attosecond pulse width synchrotron radiation pulse.
  • the laser wake field accelerator includes:
  • a gas generating device comprising an ultrashort supersonic gas nozzle J1 for generating a gas target of uniform density and adjustable density;
  • a laser beam splitting guiding device comprising a beam splitter M3, a full mirror M1, an off-axis parabolic mirror M2, and a beam splitter M3 for dividing the laser pulse L0 output by the laser source into a transmissive driving laser L1 and Processing laser L2;
  • a gas density distribution shaping device comprising a full mirror M4, M5, a light intensity spatial modulation mask SM1 and a prism pair M6, M7, and a light intensity spatial modulation mask SM1 for processing the laser L2
  • the lateral spatial light intensity distribution is modulated, and the prism pairs M6 and M7 are used to focus the processing laser L2 guided by the full mirror M5 and adjust the absolute light intensity of the processing laser L2.
  • the gas generating device, the laser splitting guide device, and the gas density distribution shaping device are all located in a vacuum chamber.
  • the outlet of the gas nozzle J1 is rectangular or circular or any other suitable shape.
  • the size of the gas target ejected from the gas nozzle J1 in the direction in which the laser is driven is generally not more than 10,000 ⁇ m, preferably 100 to 1,000 ⁇ m.
  • the splitter M3 with a transmission reflectance greater than 9:1 is divided into two sub-beams L1 and L2, and L1 as the driving laser carries more than 90% of the energy in L0.
  • L2 as a processing laser, carries only less than 10% of the energy in L0.
  • the driving laser light L1 is guided to the off-axis parabolic mirror M2 via the full-mirror M1 for focusing, and the focused driving laser light L3 is incident on the gas target.
  • the present invention requires a waist spot radius of from 10 to 100 microns, preferably from 10 to 50 microns, when the drive laser L3 reaches the front end of the gas target.
  • the prism pair M6 and M7 further focus on the processing laser L2 guided by the full mirror M5 and adjust its absolute light intensity, after focusing
  • the processing laser L4 is incident on the gas target to shape the gas density distribution of the gas target.
  • the invention requires that the processing laser is incident on the gas target perpendicular to the direction of propagation of the driving laser and can cover the entire gas target or the front end of the target.
  • the present invention requires that the high light intensity region of the processing laser corresponds to the front end of the gas target, that is, the end at which the driving laser L3 and the gas target first act; and the time t1 at which the processing laser L4 reaches the gas target should be earlier than the time t 2 at which the driving laser L3 reaches the gas target.
  • the delay time (t 2 - t 1 ) > 2 nanoseconds is required, preferably (t 2 - t 1 ) is 2-10 nanoseconds.
  • FIG. 2a illustrates the operation of the driving laser in the present invention to produce an attosecond optical pulse with a density-shaped gas target, however it should be understood that the scope of the present invention is not limited by this working principle.
  • the driving laser light L3 is incident from the left side to the density-shaped gas target T1 to generate the attosecond radiation R1.
  • the driving laser L3 excites a large amplitude plasma wave, that is, a laser tail wave, when transmitted in the gas target T1, and forms a dense tail wave electron thin layer.
  • the electron layer can be immediately injected into the wake field near the transition position of the density rising region to the platform.
  • Figure 2a shows the spatial shape EB1 of the injected electron flyer at different propagation moments.
  • the electron flyer EB1 is accelerated in the wake field and laterally contracted by the electrostatic field force to generate the coherent synchrotron radiation R1.
  • the pulse R1 has an attosecond pulse width and radiates the plasma at a certain cone angle ⁇ 0 .
  • RP1 is the projection of the attosecond pulse in the plane at different propagation moments.
  • the gas target T1 has a rising density front and a subsequent land-type density distribution along the direction of the driving laser L3, and preferably a smooth transition between the different density distributions.
  • the density gradient of the rising density front should be greater than a certain value, preferably the distance from the low density region (such as n 0 /4) to the highest density region (n 0 ) should be smaller than the wavelength of the electron plasma corresponding to the highest density region. 10 times (about 200 microns). It should be understood that the density distribution of the gas target can be in other equivalent distribution forms.
  • FIG. 3 shows a laser wake field accelerator in accordance with a second embodiment of the present invention.
  • the second embodiment differs from the first embodiment in that the laser pulse L0 generated by the laser source (not shown) does not decompose another sub-beam as a processing laser after entering the vacuum chamber.
  • a metal piece is appropriately placed at the outlet of the gas nozzle J1 to control the ejection form of the outgoing gas target (for similar operations, see the literature Phy. Rev. ST Accel. Beams, 13, 091301 (2010)).
  • the metal sheet may be a rigid sheet of metal with a sharp border, such as a razor blade.
  • the metal piece is horizontally placed at the outlet of the gas nozzle, and the area of the shielding outlet is not more than 1/2 of the entire outlet area, and the plane of the metal piece is kept parallel to the plane of the nozzle outlet by the support, and the sharp boundary of the metal piece is Gas contact.
  • the third embodiment differs from the above embodiment in that the laser pulse L0 generated by the laser source does not decompose another sub-beam as a processing laser after entering the vacuum chamber, and the metal foil control gas target is no longer placed at the outlet of the gas nozzle J1.
  • the gas nozzle is required to be an ultra-short supersonic gas nozzle of a sub-millimeter length and its outlet has a sharp edge.
  • the gas nozzle can generate a gas target with uniform gas density, and the front end boundary of the gas target rises from a vacuum to a density platform of no more than 500 micrometers.
  • the boundary size is no greater than 200 microns.
  • the difference between the above three embodiments is that the way in which the gas density rises the leading edge is different.
  • the results of the attosecond pulses generated by the three methods are substantially the same.
  • the first distribution above is an ideal distribution, which is more difficult to obtain in experiments.
  • the second and third distributions below are actual possible distributions in the experiment, and the second and third distributions can be produced by the above three embodiments.
  • the intermediate density platform followed by the platform type or the descending density distribution has little effect on the generation of the attosecond pulse.
  • the present invention employs a laser lumbar spot incidence condition that is larger than the longitudinal structure of the coda, so that the injected electron beam is a sheet-like structure having a wider lateral dimension, which is different from that obtained by the incident of a tightly focused laser pulse.
  • the attosecond pulse width electron flyer is accelerated in the wake field while being laterally subjected to a contraction motion by the action of the electrostatic field force, thereby generating coherent synchrotron radiation and having a radiation pulse width of the order of a second;
  • the present invention is capable of generating a relativistic intensity of a single attosecond optical pulse, which is different from the conventional femtosecond pulse width and incoherent radiation obtained based on laser wake field acceleration, and also breaks through existing large conventional accelerators.
  • the ability to output radiation thus providing a compact, high quality attosecond radiation source for a wide range of basic scientific and industrial applications in a relatively inexpensive and simple manner;
  • the device of the present invention is low in cost and easy to maintain.
  • the laser wake field accelerator of the present embodiment is based on the above-described first embodiment (see FIG. 1), and includes a laser splitting guide device, a gas generating device, and a gas density distribution shaping device.
  • the gas ejected from the gas nozzle J1 is hydrogen gas, and the gas molecules contain a total electron density of up to 4.7 x 10 19 per cubic centimeter.
  • the light intensity spatial modulation mask sheet SM1 has a single hole side, and the line width of the single hole is 100 ⁇ m. After further modulation by the columnar prisms M6, M7, the line width of the high-intensity region of the processing laser L4 is about 100 ⁇ m, the light intensity is about 10 14 -10 16 watts per square centimeter, and the rest of the L4 is less than 10 12 watts per square. cm.
  • the full width at half maximum of the laser pulse output by the laser source is 20 femtoseconds.
  • the laser beam L3 is incident on the gas target surface T1 with a waist spot radius of 17 ⁇ m, a peak light intensity of 7.7 ⁇ 10 19 watts per square centimeter, and a peak power of 350 TW.
  • Figures 5 and 6 show the numerical simulation results of this embodiment.
  • FIG. 5 is a result of electron acceleration and radiation of the wake field generated by driving the laser light L3 to drive the gas target T1. As shown in (a) of FIG.
  • the electron beam injected into the wake field is in a sheet-like structure (i.e., the above-mentioned electronic flyer), and the electron flyer is accelerated in the wake field while gradually contracting laterally.
  • a sheet-like structure i.e., the above-mentioned electronic flyer
  • the electron flyer is accelerated in the wake field while gradually contracting laterally.
  • Fig. 6 shows the structure of the corresponding generated attosecond radiation at different propagation moments.
  • the fine structure of the generated attosecond pulse is shown in Fig. 6.
  • the pulse width is 120 sec
  • the peak intensity is close to 3 x 10 19 watts per square centimeter
  • the total energy is 12 mJ.
  • Attoops with higher radiant intensity and energy can be obtained with an incident drive laser with a larger focal spot.
  • the attosecond pulse has complete spatiotemporal coherence, high energy, strong peak light, and pulse width generally less than 200 sec. It is suitable for a large number of basic scientific research and practical industrial applications such as single-shot imaging and heavy element ionization control of macromolecular structures. .
  • the gas target generation technology adopted in the present invention is very mature, and an ultra-short gas target of at least 200 micrometers can be realized at present.
  • the density shaping of the gas target can be achieved by various means, such as the laser processing technique of the first embodiment, even if the density-increasing boundary of the order of a hundred micrometers inherent to the gas target satisfies the requirements of the present invention.
  • the ultrashort pulse lasers of the peak power of the terawatt to the tile used in the present invention are already available from some laser manufacturers;
  • the resulting radiation quality is high: the above typical numerical results show that the method of the present invention can directly generate relativistic intensity and coherent attosecond pulse radiation, breaking through the existing pulse radiation parameters (picoseconds) that can be output based on large conventional accelerators. Pulse width, incoherent, or partially coherent);
  • the invention has low cost: the invention is based on the interaction of ultra-short-strong laser and plasma, and has the advantages of high efficiency and compactness, and the invention is very low in cost compared with the scheme based on large conventional accelerators. Compared to the scheme based on the interaction of a strong laser with a solid target, the present invention uses only a gas target, and thus has the potential to achieve high repetition rate experimentally.

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Abstract

一种激光尾波场加速器及产生高亮度阿秒光脉冲的方法。激光尾波场加速器包括用于产生驱动激光的激光源及设有气体发生装置和聚焦系统的真空室，其中气体发生装置用于产生沿驱动激光传播方向具有上升型密度前沿的气体靶（T1），而聚焦系统用于对驱动激光进行聚焦。激光源产生的驱动激光经聚焦系统聚焦后，入射到气体靶（T1），使气体靶（T1）中的气体分子被激光束电离，产生阿秒脉宽电子片注入并同步加速电子片以获得阿秒光脉冲（R1）。能产生相对论强度的阿秒光脉冲，提供阿秒辐射源。

Description

激光尾波场加速器及产生高亮度阿秒光脉冲的方法 技术领域
本发明涉及加速器和相干辐射源产生装置，具体涉及超短强激光驱动气体靶，产生高亮度阿秒光脉冲的激光尾波场加速器。
背景技术
阿秒(1阿秒＝10-18秒)光脉冲是目前实验上可获得的最短电磁辐射，它可以跟踪和操控原子尺度下的电子运动，是研究和操控微观世界的工具，例如，阿秒脉冲可以对大分子结构进行单发成像、诊断化学反应过程、鉴定药物成分等。因此发展阿秒脉冲产生技术对生命、医药、化学、材料等基础科学研究，以及尖端工业应用等均具有重要价值。高亮度阿秒脉冲的产生是目前阿秒物理的主要研究课题之一。
目前产生超短X射线脉冲比较成熟的方法是基于传统加速器的同步辐射装置和自由电子激光，如上海光源、SLAC的LCLS等。其中同步辐射装置中电子束的脉宽一般为皮秒(1皮秒＝10-12秒)至纳秒(1纳秒＝10-9秒)量级，产生的辐射具有相同量级脉宽，并且是非相干的。相干性可显著提高辐射的光子通量密度，为此，人们基于传统加速器建造了先进的X射线自由电子激光(XFEL)。XFEL输出的光脉冲峰值亮度比同步辐射源高7～9个数量级，极大拓宽了其应用潜力。例如2012年美国《科学》杂志评选出的年度十大进展就包括利用X射线激光(比同步辐射源亮10亿倍)确认了布氏锥虫所需的一种酶的结钩(这种寄生虫是引起非洲昏睡病的原因)，从而首先证明了相干X射线直接解密蛋白质的潜力。但需要指出的是，即使当前最先进的XFEL，其输出的辐射脉宽也不短于100飞秒(1飞秒＝10-15秒)，单脉冲能量不超过5毫焦耳。此外，上述基于传统加速器的辐射源装置规模庞大(数公里的加速距离)，造价昂贵(每台XFEL约10亿美元)，从而限制了面向更广泛的基础科学与工业应用。直接提供廉价、高亮度、更短脉宽的相干辐射源仍是未来加速器与辐射源领域的努力目标之一，例如，目前传统加速器学界正在探索是否可以产生阿秒脉宽的X射线脉冲。
近年来，伴随着超快激光技术的快速发展，超短强激光与等离子体相互作用在新型粒子加速和辐射源产生等方向展现出巨大潜力。等离子体可以承载高 达1011～1012伏每米的有效加速电场，比传统加速器的高3～4量级，例如强激光驱动气体靶形成的激光尾波场可在3厘米的距离将电子加速到109电子伏特，因而激光等离子体加速被认为是未来紧凑、廉价型高效加速器的热门候选之一。基于激光尾波场加速，目前已发展出多种机制产生超短X/伽玛射线脉冲，如电子束在尾波加速结构中的自发同步辐射，或与其它激光束作汤姆逊/康普顿背散射。这些高亮辐射源已被用于单发成像等应用。然而目前尾波场加速中电子注入的可控性差，通常在一定时间内准连续地发生，产生的电子束脉宽难以低于飞秒量级，因而基于这些电子束产生的辐射源也往往是飞秒脉宽、非相干的。通过激光尾波场加速获得阿秒脉宽的相干辐射亟需新的突破。
另一方面，基于超短强激光与物质的相互作用，人们已发明了多种方法来产生阿秒相干辐射，有些甚至在实验上已很成熟。例如，光强为1014～1016瓦每平方厘米的飞秒激光可有效激发气体原子高次谐波辐射，该辐射在频域表现为入射光的整数倍谐波，在时域表现为周期性的阿秒脉冲链。该方法基于激光原子过程，入射光强要求小于1016瓦每平方厘米，因而产生的阿秒脉冲强度不高。另外，相对论强度(>1018瓦每平方厘米)的超短激光与固体靶作用可以产生高强度的表面高次谐波。若对这些谐波辐射进一步作高通滤波，可以得到单个阿秒脉冲。然而，固体表面高次谐波强度通常随谐波次数的增加快速下降，所以经滤波产生单个阿秒脉冲的效率并不高。最近基于超强少周期激光与纳米靶的相互作用，人们也提出多种可以直接产生高亮度相干阿秒脉冲的方案。然而该方案要求极高的激光对比度，实验难度极大。此外，这些基于固体靶的方案也不利于高重复率运行，在实际应用上具有很大局限。
由上可见，基于强激光与等离子体相互作用产生新型辐射源比基于传统加速器的方案具有很多独特优势，但目前仍亟需一种简单易行、高重复率、激光对比度要求低的方案来直接产生高亮度、相干、阿秒光脉冲。该方案一旦实现，必将为广泛的基础科学应用等提供廉价、便捷的高品质阿秒光源，同时也将突破目前基于传统加速器输出超短辐射源的瓶颈。
发明内容
本发明的目的是提供一种相对低廉、简易的用于产生高亮度相干阿秒光脉冲的装置及方法。
根据本发明的第一方面，提供了一种用于产生阿秒光脉冲的激光尾波场加速 器，该激光尾波场加速器包括：激光源，该激光源用于产生驱动激光；和真空室，在真空室内设有气体发生装置和聚焦系统，其中，气体发生装置用于产生沿驱动激光传播方向具有上升型密度前沿的气体靶，而聚焦系统用于对驱动激光进行聚焦。激光源产生的驱动激光经聚焦系统聚焦后，入射到的气体靶，使气体靶中的气体分子被激光束电离，产生阿秒电子片注入并同步加速电子片，从而获得阿秒光脉冲。
在另一优选例中，上述密度包括总电子数密度。
在另一优选例中，具有上升型密度前沿的气体靶后接平台型或下降型密度分布。
在另一优选例中，不同密度分布之间通过中间密度平台平滑过渡。
在另一优选例中，该气体发生装置包括气体喷嘴，气体喷嘴为亚毫米长的超短超音速气体喷嘴，且气体喷嘴的出口具有锐的边界。
在另一优选例中，上述亚毫米长的超短超音速气体喷嘴喷出的气体靶的真空边缘到气体密度平台的距离不超过200微米。
在另一优选例中，该气体喷嘴的出口为长方形或圆形。
在另一优选例中，在气体喷嘴的出口设置有用于控制气体靶的喷射形态的金属片，金属片具有锐边界，金属片的锐边界与气体靶接触。
在另一优选例中，喷嘴出口方向为竖直向上，金属片水平放置于气体喷嘴的出口处，遮挡出口的面积不大于整个出口面积的1/2。
在另一优选例中，通过采用支撑物保持金属片平面与喷嘴出口平面平行、贴合。
在另一优选例中，该激光尾波场加速器还包括激光预加工系统，激光预加工系统用于向气体靶提供加工激光以对气体靶进行密度分布整形，激光预加工系统包括：空间光强调制掩模片，空间光强调制掩模片用于对加工激光的横向空间光强分布进行调制，掩模片的单孔线宽为20-500微米，较佳地50-200微米；和棱镜对，棱镜对用于对调制后的加工激光进行聚焦并调整加工激光的绝对光强；其中，经棱镜对聚焦后的加工激光沿与驱动激光的传播方向垂直的方向入射到气体靶；并且驱动激光晚于加工激光入射到气体靶，驱动激光相对加工激光入射到气体靶的延迟不小于2纳秒，较佳地该延迟为2-10纳秒。
在另一优选例中，将激光源产生的激光脉冲通过分光镜分束得到驱动激光和加工激光。
在另一优选例中，分光镜的透射反射比大于9：1，驱动激光来自激光源产生的激光脉冲经分光镜透射的激光，加工激光来自激光源产生的激光脉冲经分光镜反射的激光。
在另一优选例中，加工激光为一束或者多束低能量子束。
在另一优选例中，激光尾波场加速器还包括全反镜，用于引导驱动激光和/或加工激光。
在另一优选例中，入射到气体靶的加工激光覆盖整个气体靶或者气体靶的前端，前端指驱动激光与气体靶先作用的一端。
在另一优选例中，上述驱动激光满足以下参数：
(a)驱动激光聚焦到气体靶上的腰斑半径为微米量级，一般为10-100微米，较佳地10～50微米；
(b)驱动激光的脉宽为1～100飞秒，较佳地5～50飞秒；
(c)驱动激光的峰值功率为100～10000太瓦，较佳地200～5000太瓦。
在另一优选例中，驱动激光为基模高斯光束或超高斯光束；
在另一优选例中，该气体靶由低原子序数的单一气体或多种气体组成，较佳地为氢气、氦气或它们的混合物；
在另一优选例中，上述气体靶满足以下参数：
(a)气体靶沿驱动激光传播方向的尺寸为100～10000微米，较佳地100～1000微米；
(b)气体靶在与驱动激光传播方向垂直的方向上的一定尺度内密度均匀性好，较佳地该尺度范围为10～100微米；
(c)气体靶被电离后包含的最大电子数密度为1018～1021个每立方厘米，较佳地为1019～1020个每立方厘米；
(d)上升型密度前沿的沿驱动激光传播方向的长度为10～500微米，较佳地50-200微米。
在另一优选例中，在沿激光传播方向，该上升型密度前沿的从低密度区边界到最高密度区边界之间的距离小于最高密度对应的电子等离子体波波长的10倍(约200微米)。
在另一优选例中，上述上升型密度前沿包括低密度区(密度在0-0.25n0之间)、中密度区(密度在0.25-n0之间)和最高密度区(密度为n0)，其中n0为最高密度。
在另一优选例中，的上升型密度前沿的最低密度为0，最高密度不超过2x1020个每立方厘米。
在另一优选例中，的上升为直线上升或线性上升。
在另一优选例中，驱动激光聚焦到气体靶上的腰斑半径大于气体靶的最大电子数密度对应的电子等离子体波波长。
在另一优选例中，激光尾波场加速器产生阿秒脉宽的稠密电子飞片，即呈薄片状结构的电子束。
在另一优选例中，激光尾波场加速器产生的阿秒光脉冲具有以下特性：
(a)具有时空相干性；
(b)光强的半高全宽脉宽<500阿秒；
(c)总能量大于2毫焦耳；
(d)呈锥状形态从等离子体辐射出，相对于驱动激光传播方向锥角θ0取决于驱动激光和气体靶参数，一般为10-30度；
(e)电矢量偏振态接近径向偏振。
根据本发明的第二方面，提供了一种用于产生阿秒光脉冲的方法，该方法包括：
(a)提供脉宽为飞秒量级的驱动激光并提供沿驱动激光传播方向具有上升型密度前沿的气体靶；
(b)将驱动激光经聚焦后，产生光斑半径为微米量级的激光脉冲；
(c)将经聚焦后的激光束导入的气体靶，从而产生并加速呈薄片状结构的电子束，即电子飞片，电子飞片在尾波场中产生阿秒光脉冲。
本发明基于超短强激光驱动气体靶产生尾波场加速电子的原理，提出了一种新的尾波激发与可控的电子束注入模式，实现了阿秒脉宽、稠密电子飞片(即呈薄片状结构电子束)的注入。注入的电子飞片在尾波场中获得加速的同时产生高强度、相干阿秒脉冲。本发明具有实现技术要求低、产生的辐射品质高、成本低的优点，从而有利于为为广泛的基础科学与工业应用提供紧凑高品质的阿秒辐射源。
附图说明
图1是根据本发明第一实施方式的激光尾波场加速器的结构示意图；
图2a是本发明的产生阿秒光脉冲的工作原理示意图；
图2b是本发明所要求的气体靶电离后总电子数密度分布的可能形式；
图3是根据本发明第二实施方式的激光尾波场加速器的结构示意图；
图4是根据本发明第三实施方式的激光尾波场加速器的结构示意图；
图5示出了本发明一实施例中激光尾波场加速器产生的阿秒脉冲的典型模拟结果；
图6示出了本发明一实施例中产生的阿秒脉冲沿脉冲中心位置的典型空间结构。
具体实施方式
本发明人经过广泛而深入的研究，提出了一种结构较为简单但可高效产生高亮度相干阿秒光脉冲的装置。采用该装置，可方便而高效地产生高亮度阿秒光脉冲。在此基础上完成了本发明。
本发明提供了一种通过对气体靶的密度分布进行整形以控制电子束注入位置的装置和方法，从而在尾波场中实现阿秒脉宽电子束的注入与加速；同时，本发明采用比电子等离子体波波长更大的激光腰斑入射条件，因而注入的电子束为具有大横纵比的片状结构；产生的阿秒脉宽片状结构电子束在尾波场中加速的同时横向上受静电场力的作用而作收缩运动，因而产生相干的阿秒脉宽同步辐射脉冲。
装置及应用
下面结合附图对本发明具体实施方式作详细说明。需要指出的是，本发明并不限于以下描述，实施技术人员应从以下描述所体现的精神来理解本发明，各技术术语可以基于本发明的精神实质来做最宽泛的理解。
图1是根据本发明第一实施方式的激光尾波场加速器的结构示意图。如图1所示，激光尾波场加速器包括：
气体发生装置，该气体发生装置包括超短超音速气体喷嘴J1，气体喷嘴J1用于产生密度均匀且密度大小可调的气体靶；
激光分束引导装置，该激光分束引导装置包括分光镜M3、全反镜M1、离轴抛物面反射镜M2、分光镜M3用于将激光源输出的激光脉冲L0分为透射的驱动激光L1和加工激光L2；以及
气体密度分布整形装置，该气体密度分布整形装置包括全反镜M4、M5，光强空间调制掩模片SM1和棱镜对M6、M7，光强空间调制掩模片SM1用于对加工激光L2的横向空间光强分布进行调制，棱镜对M6、M7用于对经全反镜M5引导的加工激光L2进行聚焦并调整加工激光L2的绝对光强。
上述气体发生装置、激光分束引导装置及气体密度分布整形装置均位于真空室中。
气体喷嘴J1的出口为长方形或圆形或者其他任意合适的形状。气体喷嘴J1喷出的气体靶沿驱动激光传播方向的尺寸一般不大于10000微米，较佳地100-1000微米。
激光源(图未示)输出的激光脉冲L0进入真空室后，经透射反射比大于9：1的分光镜M3分为两个子束L1和L2，L1作为驱动激光携带L0中90％以上的能量，L2作为加工激光只携带L0中1低于10％的能量。驱动激光L1经全反镜M1引导至离轴抛物面反射镜M2进行聚焦，聚焦后的驱动激光L3入射到气体靶上。本发明要求在驱动激光L3到达气体靶前端时的腰斑半径为10-100微米，较佳地10-50微米。
加工激光L2经光强空间调制掩模片SM1进行横向空间光强分布调制后，棱镜对M6和M7对经全反镜M5引导过来的加工激光L2进一步聚焦并调整其绝对光强，经聚焦后的加工激光L4入射到气体靶上以对气体靶进行气体密度分布整形。本发明要求加工激光垂直于驱动激光的传播方向入射到气体靶，并能覆盖整个气体靶或靶的前端。此外，本发明要求加工激光的高光强区域对应气体靶的前端即驱动激光L3与气体靶先作用的一端；且加工激光L4到达气体靶的时刻t1应早于驱动激光L3到达气体靶的时刻t2，要求延时(t2-t1)>2纳秒，较佳地(t2-t1)为2-10纳秒。
为便于理解，图2a示出了本发明中驱动激光与经密度整形后的气体靶作用产生阿秒光脉冲的工作原理，然而应理解本发明的保护范围并不受该工作原理的限制。如图2a所示，驱动激光L3从左边入射到经密度整形后的气体靶T1而产生阿秒辐射R1。实验中在前述的驱动激光和气体靶参数条件下，驱动激光L3在气体靶T1中传输时激发大振幅等离子体波即激光尾波，形成致密的尾波电子薄层。该电子层在密度上升区域到平台的转换位置附近可以即时地注入尾波场。图2a示出了注入的电子飞片在不同传播时刻的空间形状EB1。电子飞片EB1在尾波场中获得加速的同时，由于受静电场力而作横向收缩运动，从而产 生类相干同步辐射R1。该脉冲R1具有阿秒脉宽并以一定锥角θ0辐射出等离子体。RP1为阿秒脉冲在不同传播时刻于平面内的投影。
如图2b所示，气体靶T1沿驱动激光L3传播方向具有上升型密度前沿和后接的平台型密度分布，较佳地不同密度分布之间可为平滑过渡。上升型密度前沿的密度梯度应大于一定值，较佳地从低密度区(如n0/4)到最高密度区(n0)之间的距离应小于最高密度区对应的电子等离子体的波长的10倍(约200微米)。应理解气体靶的密度分布可为其他等价的分布形式。
图3示出了根据本发明第二实施方式的激光尾波场加速器。第二实施方式与第一实施方式的区别在于：激光源(图未示)产生的激光脉冲L0进入真空室后不再分解出另一子束作为加工激光。第二实施方式中，仅在所述气体喷嘴J1的出口适当放置一金属片来控制出射气体靶的喷射形态(类似操作参见文献Phy.Rev.ST Accel.Beams,13,091301(2010))，从而产生本发明要求的气体(等离子体)密度分布。金属片可以是刚性好、具有锐边界的金属薄片，例如剃须刀片。金属片水平放置于气体喷嘴出口处，遮挡出口的面积不大于整个出口面积的1/2，并通过采用支撑物保持金属片平面与喷嘴出口平面平行、贴合，同时金属片的锐边界一边与气体接触。
图4示出了根据本发明第三实施方式的激光尾波场加速器。第三实施方式与上述实施方式的区别在于：激光源产生的激光脉冲L0进入真空室后不再分解出另一子束作为加工激光，也不再在气体喷嘴J1出口放置金属薄片控制来气体靶的喷射形态。在第三实施方式中，要求气体喷嘴为亚毫米长的超短超音速气体喷嘴且其出口具有锐的边缘。该气体喷嘴能产生气体密度均匀性好的气体靶，气体靶前端边界从真空上升到密度平台的尺寸不大于500微米。较佳地，该边界尺寸不大于200微米。
上述三种实施方式的区别在于产生气体密度上升前沿的方式不同，理论上如果其他参数一致，通过这三种方式产生的阿秒脉冲结果基本相同。图2b中，上方的第一分布为理想分布，实验中较难获得。下方的第二、第三分布为实验中实际可能的分布，通过上述三种实施方式均可以产生第二、第三分布。中间密度平台后接平台型或下降型密度分布对阿秒脉冲的产生几乎没有影响。
本发明与现有技术相比，主要区别及其效果在于：
(a)通常紧聚焦激光脉冲驱动的尾波场加速方案中，电子注入在一定时间 范围内准连续地发生，导致最终注入的电子束具有飞秒脉宽，因而产生的辐射也相应地具有飞秒量级的脉宽，并且是非相干的。本发明提供了一种通过气体密度整形靶控制电子束注入位置的方法，从而在尾波场中实现阿秒脉宽电子束的注入与加速；
(b)本发明采用比尾波纵向结构尺寸更大的激光腰斑入射条件，因而注入的电子束为具有较宽横向尺度的片状结构，不同于通常紧聚焦激光脉冲入射情况下得到的大纵横比的束状结构；
(c)所述阿秒脉宽电子飞片在尾波场中加速的同时横向上受静电场力的作用而作收缩运动，因而产生相干的同步辐射且辐射脉宽为阿秒量级；
(d)与基于激光与固体靶相互作用的方案相比，本发明仅使用气体靶，因而在实验上具备高重复率实现的潜力；
(e)本发明能产生相对论强度的单个阿秒光脉冲，不同于以往基于激光尾波场加速通常所得到的飞秒脉宽、非相干辐射，同时也突破了现有的基于大型传统加速器所能输出辐射的能力，因而能以相对低廉、简易的方法为广泛的基础科学与工业应用提供紧凑高品质的阿秒辐射源；
(f)本发明装置的成本低、维护简便。
下面结合具体实施例，进一步阐述本发明。应理解，这些实施例仅用于说明本发明而不用于限制本发明的范围。下列实施例中未注明具体条件的实验方法，通常按照常规条件，或按照制造厂商所建议的条件。
实施例
本实施例的激光尾波场加速器基于上述第一实施方式(参见图1)，包括激光分束引导装置、气体发生装置和气体密度分布整形装置。
本实施例中，气体喷嘴J1喷出的气体为氢气，气体分子包含的总电子密度最高为4.7x1019个每立方厘米。
光强空间调制掩模片SM1具有单孔侧边，单孔的线宽为100微米。经柱状棱镜M6，M7进一步调制后，加工激光L4的高光强区域线宽约为100微米，光强约为1014-1016瓦每平方厘米，L4的其余部分光强低于1012瓦每平方厘米。
本实施例中，激光源输出的激光脉冲的半高全宽值为20飞秒。经离轴抛物面反射镜M2聚焦后，驱动激光L3入射到气体靶面T1时的腰斑半径为17微 米，峰值光强为7.7x1019瓦每平方厘米，峰值功率为350TW。图5和图6示出了本实施例的数值模拟结果。图5是驱动激光L3驱动气体靶T1产生的尾波场电子加速与辐射结果。如图5中(a)所示，根据本发明的基本原理，注入尾波场的电子束呈薄片状结构(即上述电子飞片)，电子飞片在尾波场中获得加速同时横向逐渐收缩。图5中(b)示出了相应产生的阿秒辐射在不同传播时刻的结构。产生的阿秒脉冲的精细结构如图6所示，脉宽为120阿秒，峰值光强接近3x1019瓦每平方厘米，总能量为12毫焦。在三维情形下，该阿秒脉冲以θ0＝10度的立体锥角从等离子体辐射出来。采用更大焦斑的入射驱动激光可以获得具有更高辐射强度和能量的阿秒脉冲。该阿秒脉冲具有完全的时空相干性，且能量高、峰值光强大、脉宽一般小于200阿秒，适合大分子结构的单发成像、重元素离化控制等大量基础科学研究与实际工业应用。
本发明的激光尾波场加速器及产生高亮度阿秒光脉冲的方法具有以下优点：
实现技术要求低：本发明采用的气体靶发生技术已很成熟，目前已能实现最短200微米的超短气体靶。气体靶的密度整形可通过多种手段实现，如第一实施方式中的激光加工技术，即使是气体靶固有的百微米量级的密度上升型边界也可满足本发明的要求。本发明所使用的百太瓦至拍瓦峰值功率的超短脉冲激光器已经可从某些激光器生产商订购；
产生的辐射品质高：上述典型的数值结果表明，采用本发明的方法，可以直接产生相对论强度、相干阿秒脉冲辐射，突破了现有的基于大型传统加速器所能输出的脉冲辐射参数(皮秒脉宽、非相干、或部分相干)；
成本低：本发明基于超短强激光与等离子体相互作用，具有高效、紧凑等优势，相对基于大型传统加速器的方案，本发明成本非常低。与基于强激光与固体靶相互作用的方案相比，本发明仅使用气体靶，因而在实验上具备高重复率实现的潜力。
应理解，在阅读了本发明的上述讲授内容之后，本领域技术人员可以对本发明作各种改动或修改，这些等价形式同样属于本申请所附权利要求书所限定的范围。

Claims (10)

  1. 一种用于产生阿秒光脉冲的激光尾波场加速器，其特征在于，所述激光尾波场加速器包括：
    激光源，所述激光源用于产生驱动激光；和
    真空室，所述真空室内设有气体发生装置和聚焦系统，其中，所述气体发生装置用于产生沿驱动激光传播方向具有上升型密度前沿的气体靶，而所述聚焦系统用于对驱动激光进行聚焦；其中，
    所述激光源产生的驱动激光经所述聚焦系统聚焦后，入射到所述的气体靶，使所述气体靶中的气体分子被所述激光束电离，产生阿秒电子片注入并同步加速电子片，从而获得阿秒光脉冲。
  2. 如权利要求1所述的激光尾波场加速器，其特征在于，所述气体发生装置包括气体喷嘴，所述气体喷嘴为亚毫米长的超短超音速气体喷嘴，并且所述气体喷嘴的出口具有锐的边界。
  3. 如权利要求1所述的激光尾波场加速器，其特征在于，所述气体发生装置包括气体喷嘴，在所述气体喷嘴的出口设置有用于控制所述气体靶的喷射形态的金属片，所述金属片具有锐边界，金属片的所述锐边界与所述气体靶接触。
  4. 如权利要求1所述的激光尾波场加速器，其特征在于，所述激光尾波场加速器还包括激光预加工系统，所述激光预加工系统用于向所述气体靶提供加工激光以对气体靶进行密度分布整形，所述激光预加工系统包括：
    空间光强调制掩模片，所述空间光强调制掩模片用于对所述加工激光的横向空间光强分布进行调制，所述掩模片的单孔线宽为20-500微米，较佳地50-200微米；和
    棱镜对，所述棱镜对用于对调制后的加工激光进行聚焦并调整所述加工激光的绝对光强；
    其中，经棱镜对聚焦后的加工激光沿与驱动激光的传播方向垂直的方向入射到气体靶；并且
    所述驱动激光晚于加工激光入射到气体靶，驱动激光相对加工激光入射到气体靶的延迟不小于2纳秒，较佳地该延迟为2-10纳秒。
  5. 如前述权利要求中任一项所述的激光尾波场加速器，其特征在于，所述驱动激光满足以下参数：
    (a)所述驱动激光聚焦到气体靶上的腰斑半径为微米量级，一般为10-100微米，较佳地10～50微米；
    (b)所述驱动激光的脉宽为1～100飞秒，较佳地5～50飞秒；
    (c)所述驱动激光的峰值功率为100～10000太瓦，较佳地200～5000太瓦。
  6. 如前述权利要求中任一项所述的激光尾波场加速器，其特征在于，所述气体靶满足以下参数：
    (a)所述气体靶沿所述驱动激光传播方向的尺寸为100～10000微米，较佳地100～1000微米；
    (b)所述气体靶在与所述驱动激光传播方向垂直的方向上的一定尺度内密度均匀性好，较佳地该尺度范围为10～100微米；
    (c)所述气体靶被电离后包含的最大电子数密度为1018～1021个每立方厘米，较佳地为1019～1020个每立方厘米；
    (d)所述上升型密度前沿的沿驱动激光传播方向的长度为10～500微米，较佳地50-200微米。
  7. 如前述权利要求中任一项所述的激光尾波场加速器，其特征在于，所述驱动激光聚焦到气体靶上的腰斑半径大于所述气体靶的最大电子数密度对应的电子等离子体波波长。
  8. 如前述权利要求中任一项所述的激光尾波场加速器，其特征在于，所述激光尾波场加速器产生阿秒脉宽的稠密电子飞片，即呈薄片状结构的电子束。
  9. 如前述权利要求中任一项所述的激光尾波场加速器，其特征在于，所述激光尾波场加速器产生的阿秒光脉冲具有以下特性：
    (a)具有时空相干性；
    (b)光强的半高全宽脉宽<500阿秒；
    (c)总能量大于2毫焦耳；
    (d)呈锥状形态从等离子体辐射出，相对于驱动激光传播方向锥角θ0取决于驱动激光和气体靶参数，一般为10-30度；
    (e)电矢量偏振态接近径向偏振。
  10. 一种用于产生阿秒光脉冲的方法，其特征在于，所述方法包括：
    (a)提供脉宽为飞秒量级的驱动激光并提供沿驱动激光传播方向具有上升型密度前沿的气体靶；
    (b)将所述驱动激光经聚焦后，产生光斑半径为微米量级的激光脉冲；
    (c)将经聚焦后的激光束导入所述的气体靶，从而产生并加速呈薄片状结构的电子束，即电子飞片，所述电子飞片在尾波场中产生阿秒光脉冲。
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CN105977785A (zh) * 2016-03-25 2016-09-28 中国科学院等离子体物理研究所 一种基于激光尾波场和沟道效应的光子辐射源产生方法
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CN106873022A (zh) * 2017-03-20 2017-06-20 中国科学院上海光学精密机械研究所 一种适用于激光尾场电子加速的高分辨率电子能谱仪
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