This PDF file contains the front matter associated with SPIE Proceedings Volume 11036, including the title page, copyright information, table of contents, and author and committee lists.

Laser amplification through plasma-based techniques might overcome the thermal damage limit of conventional materials, thereby enabling the next generation of laser intensities. The leading plasma-based method is Raman compression: a long laser pump decays into a plasma wave and a counterpropagating short laser seed pulse, which, capturing the pump energy, reaches extreme intensities. The technological requirements on the seed are severe: it must be very sharp and matched properly in frequency. To sharpen the seed pulse, we propose a laser-controlled, super-fast plasma shutter technique, analogous to electromagnetically induced transparency (EIT) in atoms. We further show that the laser seed may even be replaced by a stationary plasma wave seed. In the important pump-depletion regime, the plasma-wave initiated output pulse approaches the self-similar attractor solution for the corresponding laser seed, with the frequency match automatic. These techniques also work with partially coherent pumps. Actually, a partially coherent pump can even advantageously suppress the noise-seeded spontaneous Raman amplification which is responsible for premature pump depletion.

The increasing demand for high laser powers is placing huge demands on current laser technology. This is now reaching a limit, and to realise the existing new areas of research promised at high intensities, new cost-effective and technically feasible ways of scaling up the laser power will be required. Plasma-based laser amplifiers may represent the required breakthrough to reach powers of tens of petawatts to exawatts, because of the fundamental advantage that amplification and compression can be realised simultaneously in a plasma medium, which is also robust and resistant to damage, unlike conventional amplifying media. Raman amplification is a promising method, where a long pump pulse transfers energy to a lower frequency, short duration counter-propagating seed pulse through resonant excitation of a plasma wave that creates a transient plasma echelon, which backscatters the pump into the probe. While very efficient, this comes at the cost of noise amplification (from plasma density fluctuations) that needs to be controlled. Here we present the results of an experimental campaign where we have demonstrated chirped pulse Raman amplification (CPRA) at high intensities. We have used a frequency chirped pump pulse to limit the growth of noise amplification, while trying to maintain the amplification of the seed. In non-optimised conditions we show that indeed noise amplification can be controlled but reducing noise scattering also limits the seed amplification factor. Finally, we show that the gross efficiency is a few percent, consistent with previous measurements of CPRA obtained in capillaries with pump pulses of duration of a few hundred picoseconds.

There is significant international effort focussed on developing ultra-high-power systems for next-generation laser facilities, such as the Extreme Light Infrastructure (ELI). Existing amplification methods are based on chirped-pulse amplification (CPA). However, the low damage threshold of conventional solid-state optics results in very large amplifiers and compressors. To overcome this challenge, we use stimulated Raman backscattering of a long pump laser in plasma to provide amplification for a low intensity seed pulse. Plasma has the advantage that it is already a broken down medium and therefore field intensities are not constrained as they are in conventional laser amplifiers. This offers the potential to reduce the size and cost of these devices significantly, while providing a possible route to reach exawatt powers, which will enable investigation of extremely high field physics. Despite its advantages, efficient Raman amplification has not yet been demonstrated experimentally. Efficiencies are limited to only a few percent for seed energies of a few mJ, in contrast with theoretical predictions. Several phenomena lead to saturation or inhibit the amplification process – such as detuning, wavebreaking and particle trapping – depending on the amplification regime. Amplification is therefore highly sensitive to the conditions and parameters used. Raman amplification experiments are challenging, and careful planning is required to ensure that controlled and sustained amplification can take place. Numerical simulation is an essential ingredient to this preparation yet, like the experiments themselves, this is not a trivial task. The amplification process takes place over several millimetres, while structures on the short beat wavelength of the lasers need to be adequately resolved. Since particle kinetic effects are also important, a large number of particles are required. Simulation of the entire domain therefore requires significant computing resources, and therefore many investigations are only performed in 1-dimension. Moreover, the long propagation times involved allow numerical artefacts from processes such as grid heating or numerical dispersion to become significant. These can become pathological and artificially seed or disturb the amplification process. Using state-of-the-art numerical techniques, we investigate the amplification of low- and high-intensity seed pulses in plasma, and compare their amplification growth rates and efficiencies with experimental results obtained by our group. The use of a chirped pump laser pulses is discussed and compared.

We present an investigation into counter-streaming electron beams converging towards, and diverging from, a single point in two dimensions, leading to two-stream and current filamentation instabilities, which have radial and azimuthal density modulations, respectively. Using a semi-analytical approach and numerical simulations, we find no evidence for the two-stream instability in this geometry, but show that the system is unstable to the development of current filamentation.

Recent development of PW laser and ion acceleration in SKL in SIOM The recent developments of the PW laser system (SULF) and ion acceleration in State Key Laboratory (SKL) of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics (SIOM) are introduced. A double beam image (DBI) technique is coupled in the two-stage accelerating mechanism to simultaneously improve the spectra and maximum energy of the proton beam. The cascaded shock acceleration mechanism and the cascaded TNSA mechanism work together to generate a proton beam with a narrow-spectrum center at 5.4 MeV and a long tail up to 14.4 MeV. Experimental and simulation results show that spatial collineation, time synchronization, and real-time monitoring are needed for optimum two-stage proton acceleration and are realized by the DBI technique to a certain extent in our experiment. Depending on DBI, the narrow spectral ion beam with low charge-to-mass (C2+) generated by triple-stage acceleration mechanism are also investigated by a simple numerical model and partially verified by the experiment. In addition, some new manipulations on particles are investigated by the Laguerre–Gaussian (LG) laser in the relativistic region, which are subverted from the classical tweezers, spanner, or wrench driven by the weak LG light or LG laser in previous studies.

When coherent electromagnetic radiation generated by powerful laser system is tightly focused, pursuing the aim to achieve the highest value of intensity possible, it may be challenging estimating this intensity with a sufficient degree of accuracy. If the energy of a laser pulse, its duration, time profile and focal spot radius are known, evaulation of the maximal intensity is straightforward. However, for high power (sub-petawatt and above) femtosecond laser systems, the inherent uncertainties of these four parameters (except maybe the pulse duration) are rather high, so that different estimation models of the laser intensity in the focus may substantially disagree. Presently, the question of whether or not intensities above 10^21 W/cm2 have ever been achieved remains debatable, although values of this order and above are the main goal of the two Extreme Light Infrastructure (ELI) pillars. In this context, a reliable method allowing to calibrate ultrahigh laser intensities becomes of even higher demand. Here we discuss the reliability of a method for the measurement of ultrahigh laser intensities, based on the effect of tunneling field ionization of heavy atoms and ions. To this end, we employ the highly nonlinear dependence of tunneling ionization rates on the laser intensity. This nonlinearity leads to the emergence of steep plateaus in the distribution of charge states in the laser focus and in such a way to allowing estimate, with a high degree of certainty, the laser intensity at focus.

We review the results obtained with the INRS laser system on the scaling of X-ray sources based on laser wake-field acceleration (LWFA) of electrons. We have successfully generated stable propagation in gas jets of a relativistic pulse through self-guiding on length well larger than the classical LWFA dephasing and depletion lengths, generating very intense beams of hard X-rays with 200TW on target. Our experimental scaling law obtained for the photon yield is presented and the level of X-ray emission in a 30keV-40keV band at the 1PW laser peak power level, now available at several laser facilities, is estimated.

Laser wakefield accelerators (LWFA) hold great potential to produce high-quality high-energy electron beams (e beams), and wiggling of these LWFA e beams either in the Conventional period magnetic field structure (undulator radiations), strong focusing laser wakefield (betatron radiation), or intense laser fields (Compton scattering) can emit high-energy x-ray photons. By experimentally generating the high-quality LWFA e beams with a good stability and repeatability, we have recently produced tunable quasi-monochromatic ultrahigh brilliance MeV γ-ray via the self-synchronized all-optical Compton scattering scheme and realized a scheme to enhance betatron radiation by manipulating transverse oscillation of electrons in a deflected wakefield with a tilted shock front. We also redeveloped and optimized the 200TW laser system to generate the high-stability electron beams, which may realize the compact and coherent x-ray free-electron-laser. The concurrent generation of high-quality e beams and bright x-rays in a compact LWFA may provide practical applications in ultrafast pump-probe study and x-ray radiology fields.

The laser wake-field accelerator (LWFA) traditionally produces high brightness, quasi-monoenergetic electron beams with Gaussian-like spatial and angular distributions. In the present work we investigate the generation of ultra-relativistic beams with ring-like structures in the blowout regime of the LWFA using a dual stage accelerator. A density down-ramp triggers injection after the first stage and is used to produce ring-like electron spectra in the 300 - 600 MeV energy range. These well defined, annular beams are observed simultaneously with the on-axis, high energy electron beams, with a divergence of a few milliradians. The rings have quasi-monoenergetic energy spectra with an RMS spread estimated to be less than 5%. Particle-in-cell simulations confirm that off-axis injection provides the electrons with the initial transverse momentum necessary to undertake distinct betatron oscillations within the plasma bubble during their acceleration process.

Plasma-based particle accelerators are now able to provide the scientific community with novel light sources. Their applications span many disciplines, including high energy density sciences, where they can be used as probes to explore the physics of dense plasmas and warm dense matter. The development and improvement of these light sources continues to be of great interest for the plasma physics community. This talk will present their experimental and theoretical characterization in a regime where little is known about their properties. In Self-modulated laser wakefield acceleration (SMLWFA), electrons are accelerated in a plasma wave driven by a long laser pulse broken up into a train of short pulses, each of these having a width on the order of a plasma period. Our recent experimental and theoretical work shows that we can use three mechanisms to produce high energy x-rays and gamma-rays from SMLWFA: Betatron motion of electrons, Bremsstrahlung, and inverse Compton scattering. A series of experiments at the LLNL Jupiter Laser Facility, using the 1 ps 150 J Titan laser, have demonstrated low divergence electron beams with energies up to more than 300 MeV and 10’s nCs of charge, and betatron x-rays with critical energies up to 20 keV. These experiments have led to important advances in understanding the details of the x-ray generating mechanisms and some of the most detailed characterization of the associated x-ray emission. New experiments have demonstrated using Compton scattering and Bremsstrahlung to generate >100 keV x-rays. This study presents the results of several highly successful experiments and associated theory and provides important understanding of these three sources. This work is an important step toward their development on large-scale international laser facilities, and also opens the prospect of using them for applications.

A compact light source can be utilized by using an electron beam from a Laser wakefield accelerator, of which merits are smaller size, lower radiation hazard with local shielding, and lower cost compared to conventional RF accelerators. To use as an injector for an accelerator, such as, storage rings or linacs, the high vacuum environment is important for longer lifetime in a cycle accelerator and higher repetition operation. The use of metallic target was suggested [1] and demonstrated using 30 TW fs laser system at KAERI [2,3]. The results showed not only the possibility of high-vacuum, high-repetition operations, but also high stability in beam energy and beam pointing. Due to the optical ionization process up to Al+11 by main laser of the pre-plasma, which is laser ablated plasma typically ionized Al+3 ~ Al+5 by ns laser, the mechanism of laser electron acceleration is different to fully ionized gas target like He gas. The simulation result shows the difference between the fully ionized plasma and partially ionized plasma. We present the experimental and simulation results and discuss the issues on target materials and the possibility of multistage operation. [1] Ya. V. Getmanov, O. A. Shevchenko, N. A. Vinokurov, "Electron injection into a cyclic accelerator using laser wakefield acceleration," Proceedings of IPAC’10, Kyoto, Japan, 1503-1505 (2010). [2] Jaehoon Kim, Younghun Hwangbo, Woo-Je Ryu, Kyung Nam Kim, and Seong Hee Park, “Density profile of a line plasma generated by laser ablation for laser wakefield acceleration,” Journal of Instrumentation 11, C03012 (2016). [3] Seong Hee Park et. al, to be submitted.

The plasma mirror (PM) is an ideal model system to study relativistic optics; its geometry is simple, and its dynamics is rich and non-linear. Emphasized by high-order harmonic generation (HHG), relativistic PMs are a promising next-generation EUV source, unbounded in brightness and band-width. The applicability of these sources, however, is impeded at present because of the stringent requirement on laser intensity and temporal contrast. To-date, PM-HHG at the relativistic regime are only generated using post-compression contrast enhancement, commonly in the form of a PM-optical-switch. The complexity and low efficiency of this approach impose even stronger requirement on laser peak-power. I will present our progress towards PM-HHG in the relativistic regime using the newly commissioned 20 TW laser system at Tel-Aviv University. The laser’s architecture is based on Picosecond Optical Parametric Chirped Pulse Amplification (Ps-OPCPA) for most of the system gain, followed by a traditional Ti:Sapphire power amplifier. In Ps-OPCPA the seed pulse is amplified in a picosecond window, enhancing contrast and eliminating pre-pulses associated with the use of classic regenerative amplifiers. These result in temporal laser contrast better than 1010 on 50 picosecond time scale. Owing to this pristine contrast, we demonstrated PM-HHG directly without post-compression contrast enhancement. I will present our method for controlling the spatial phase properties of the harmonics by tailoring the focused laser intensity profile. This method is based on a beam shaping technique which employs a two-optical-paths mirror that adds a half-cycle phase to the center of the beam. A variable aperture controls the fraction of laser energy outside the phase-shifted region. By changing the aperture diameter, the focal spot profile can be manipulated from gaussian to flat-top to donut shape. Owing to strong correlation between laser intensity and HHG phase, the tailored intensity profile is mapped into the HHG spatial phase profile, changing the far field properties of the EUV beam. Our aim is to minimize the angular divergence of the generated harmonics, forming the next step towards making these sources applicable. Preliminary results towards this goal will be presented.

Development of laser-plasma X-ray sources provides a new route to high brightness and small source size somewhere in the middle of low cost micro-focus X-rays and large scale synchrotron facilities. We explore one application of this new type of sources with emphasis on the stability of the source at high repetition rate and the advantage over similar conventional sources. In this paper we report the development and application of a micro-focus X-ray source for phase contrast imaging. The X-ray source produced at the Laser Laboratory for Acceleration and Applications (L2A2) of the University of Santiago de Compostela (USC), is made by focusing a 1 mJ, 35 fs, 1kHz pulses at 800 nm wavelength on metallic plates close to the diffraction limit. The X-ray spectra of this source are characterized by the K-α peaks which can be 'tuned' by changing the target material and a Bremsstrahlung continuum up to several tens of keV. The stability of the source is achieved by optimizing the positioning system of the metallic target which refresh and keep the surface within the small the Rayleigh length allowing the development of applications.

Wakefield excited by intense lasers or charged particle beams in plasmas has made great strides recent years in demonstrating high-gradient acceleration of electron and positron beams, showing its tremendous potential in revolutionizing the design of next-generation compact light sources and colliders. In a plasma wakefield accelerator, the wakefield essentially serves as an "accelerator" for the witness beam, at the same time a "decelerator" for the driver. For a beam driver, the deceleration is simply the effect of the deceleration field. But for a laser driver, photons do not feel a deceleration field directly, instead they deplete their energy via frequency downshifting on a refractive index gradient, leading to a slowing down of their group velocity, literally behaving like “a photon decelerator”. In fact, theory and simulations suggest that such a photon decelerator with a properly designed plasma structure could serve as an ideal nonlinear optical device for the generation of intense single-cycle broadband long-wavelength infrared (IR) pulses. Here we successfully demonstrate this novel scheme in experiments. An intense single-cycle IR pulse with a central wavelength of 9.4 µm and energy of 3.4 mJ is generated using a ~580 mJ, 36 fs, 810 nm drive laser. Furthermore, the tunability of the IR wavelength in the range of 4-15µm is also successfully demonstrated through simple adjustment of the plasma structure. This relativistically intense, ultra-broadband infrared pulse opens up many opportunities for relativistic-infrared nonlinear optics, attosecond X-ray pulses via high-harmonic generation, and pump-probe experiments in the “molecular fingerprint” region. References: [1] Zan Nie, Chih-Hao Pai, Jianfei Hua, et al., “Relativistic single-cycle tunable infrared pulses generated from a tailored plasma density structure”, Nature Photon., 12: 489, 2018 [2] Zan Nie, et al., to be submitted

Laser-wakefield accelerators generate femtosecond-duration electron bunches with energies from 10s of MeV to several GeV in millimetre distances by exploiting the large accelerating gradients created when a high-intensity laser pulse propagates in an underdense plasma. The process governing the formation of the accelerating structure (bubble") also causes the generation of sub-picosecond duration, 1-2 MeV nanocoulomb electron beams emitted obliquely into a hollow cone around the laser propagation axis. We present simulations showing that these wide-angle beams can be used to produce coherent transition radiation in the 0.1-5 THz frequency range with 10s μJ to mJ-level energy if passed through an inserted metal foil, or directly at the plasma-vacuum interface. We investigate how the properties of terahertz radiation change with foil size, position and orientation. The bunch length and size of wide-angle beams increase quickly as the electrons leave the accelerator, causing a shift of the radiation frequency peak from about 1 THz at a distance of 0.1 mm from the accelerator exit to 0.2 THz at 1 mm. If the foil size is reduced, for example to match the typical diameter of the plasma channel formed in a laser-wakefield accelerator, simulating the emission from the plasma-vacuum boundary, the low-frequency side of the spectrum is suppressed. The charge of wide-angle electron beams is expected to increase linearly with the laser intensity, with a corresponding quadratic increase of the terahertz radiation energy, potentially paving the way for mJ-level sources of coherent terahertz radiation.

It is well known that an infinite homogeneous Langmuir wave, formed by accelerating charged particles, it does not emit electromagnetic radiation because of its electrostatic nature, which is represented by the zero curl of the electric field. To realise emission, the plasma density must be tailored such that the Langmuir wave takes on a non-zero component of the curl of the electric field. The mechanisms of inverse mode conversion or travelling wave antennae leads to emission of radiation. In these mechanisms, the emphasis is on energy conversion of the Langmuir ‘wave’ to an electromagnetic wave. However, an interesting way to cause the plasma wave to emit radiation is to isolate a single ‘oscillator’ composed of a localized plasma block, i.e., a plasma dipole. An outstanding question in the realization of this idea is how to isolate the plasma oscillation from the Langmuir wave. To answer this question, we propose a novel idea of colliding detuned counter-propagating laser pulses in plasma. Simulation results show that radiation is emitted from the isolated plasma dipole.

Stimulated electron self-injection in the laser wakefield accelerator (LWFA) using density downramps is well known and regularly used to produce high energy electron bunches. The use of density gradients not only to stimulate injection but also control the properties of the injected electron bunch was recently presented by Tooley et al. [Phys. Rev. Lett. 119, 044801 (2017)], in which the authors put forward a model for controlling the velocity of the back of the bubble and compared to 2D and 3D particle-in-cell (PIC) data. This model is discussed and used to identify suitable LWFA parameters for ultra-short injection and repeated injection of multiple bunches. Quasi-3D PIC data is used to demonstrate injection of multiple bunches well separated in energy.

Emergence of ultrafast EUV to X-ray sources, Free Electron Laser, High harmonic generation, betatron and Compton, has opened new paradigms in physical, chemical, biological and medical sciences by either producing ultrahigh intensities or for ultrafast imaging or by enabling pump-probe experiments at new timescales. Most of these experiments require an excellent or at least a properly defined wavefront (WF). A number of WF sensing techniques have been proposed in the X-Rays, including grating-based interferometry, speckle tracking, pencil beam deflectometry, or curvature sensors. Among these techniques, Hartmann WF sensing demonstrated a number of advantages, such as insensitivity to vibrations, achromaticity and very large dynamic range. Furthermore, the phase and intensity maps are directly retrieve and nearly instantaneously without the use of complex and long algorithms. Imagine Optic developed EUV to X-ray WF sensors since more than 15 years taking benefit of decades of experience in the visible range. We will show several experiments using our EUV sensors for metrology and optimization of ultrafast EUV sources. We recently developed a Hartmann sensor in the 5 - 25keV range. The device is based on a custom scintillator-to-detector optical relay system, as well as on an optimal Hartmann array geometry, providing 20µm spatial WF sampling resolution, over a 3x3 mm² pupil. We show the results of first experiments on a synchrotron beamline at 10 keV, achieving 4pm WF repeatability.

Laser plasma accelerators are highly versatile and are sources of both radiation and particle beams, with unique properties. The Scottish Centre for Application based Plasma Accelerators (SCAPA) 40 TW and 350 TW laser at the University of Strathclyde has been used to produce both soft and hard x-rays using a laser wakefield accelerator (LWFA). The inherent characteristics of these femtosecond duration pulsed x-rays make them ideal for probing matter and ultrafast imaging applications. To support the development of applications of laser plasma accelerators at the SCAPA facility an adjustable Kirkpatrick-Baez x-ray microscope has been designed to focus 50 eV - 10 KeV x-rays. It is now possible to produce high quality at silicon wafers substrates that can be used for x-ray optics. Platinum-coated (40 nm) silicon wafers have been used in the KB instrument to image the LWFA x-ray source. We simulate the source distribution as part of an investigation to determine the x-ray source size and therefore its transverse coherence and ultimately the peak brilliance. The OASYS SHAODOW-OUI raytracing and wave propagation code has been used to simulate the imaging setup and determine instrument resolution.

High energy attosecond electron bunches from the laser-plasma wakefield accelerator (LWFA) are potentially useful sources of ultra-short duration X-rays pulses, which can be used for ultrafast imaging of electron motion in biological and physical systems. Electron injection in the LWFA depends on the plasma density and gradient, and the laser intensity. Recent research has shown that injection of attosecond electron bunches is possible using a short plasma density ramp. For controlled injection it is necessary to keep both the laser intensity and background plasma density constant, but set to just below the threshold for injection. This ensures that injection is only triggered by an imposed density perturbation; the peak density should also not exceed the threshold for injection. A density gradient that only persists over a short range can lead to the injection of femtosecond duration bunches, which are then Lorentz contracted to attoseconds on injection. We consider an example of a sin² shaped modulation where the gradient varies until the downward slope exceeds the threshold for injection and then reduces subsequently to prevent any further injection. The persistence above the threshold determines the injected bunch length, which can be varied. We consider several designs of plasma media including density perturbations formed by shaped Laval nozzles and present an experimental and theoretical study of the modulated media suitable for producing attosecond-duration electron bunches.

One challenge in X-ray optics is how to focus hard X-rays. The possibility of achieving a wide-range of spot sizes would be an advantage for many applications, such as semiconductor lithography, nuclear fusion diagnostics or focused X-ray beams for cancer therapy. Focused X-rays could deliver precise high doses to tumours while sparing the surrounding tissue. Currently, a promising approach is using a Laue lens. However, they are limited by the diffraction capability of crystals and the complex mm-size arrangement of the optical elements. In addition, they are restricted to sub-MeV photon beams, because for higher energies the Bragg condition is not satisfied. We present an efficient and cost-effective method to extend this range up to tens of MeV using an electron-photon converter in the stream of focused high energy electrons. The emerging X-rays follow the trajectories of the electrons and the focus can be simply adjusted by modifying the focus of the electron beam. A bending magnet can be used to remove electrons, if necessary, however a mixed radiation could be an additional option. Our solution can also be adapted to a multiple beam arrangement as an effective alternative to Gamma Knife without the need for handling radioactive sources.

The Scottish Centre for the Application of Plasma-based Accelerators (SCAPA) is a research centre dedicated to providing high energy particle beams and high peak brightness radiation pulses for users across all scientific and engineering disciplines. A pair of Ti:Sapphire femtosecond laser systems (40 TW peak power at 10 Hz pulse repetition rate and 350 TW at 5 Hz, respectively) are the drivers for a suite of laser-plasma accelerator beamlines housed across a series of radiation shielded areas. The petawatt-scale laser delivers 45 W of average power that establishes it as the world leader in its class. The University of Strathclyde has had an operational laser wakefield accelerator since 2007 as the centrepiece of the ongoing Advanced Laser Plasma High-energy Accelerators towards X-rays (ALPHA-X) project. SCAPA, which is a multipartner venture under the auspices of the Scottish Universities Physics Alliance, continues the dedicated beamline approach pioneered by ALPHA-X and represents a significant expansion in the UK’s experimental capability at the university level in laser-driven acceleration. The new centre supports seven radiation beamlines across three concrete shielded bunkers that each nominally specialise in a different aspect of fundamental laser-plasma interaction physics and radiation sources: GeVscale electron beams, MeV/c proton and ion beams, X-rays, gamma rays and so on. Development of application programmes based on these sources cover a wide range of fields including nuclear physics, radiotherapy, space radiation reproduction, warm dense matter, high field physics and radioisotope generation.

In this letter, a method using off-resonance laser modulation is proposed for the generation of coherent harmonic radiation. The off-resonant seed laser, whose wavelength is different from the resonant wavelength of the modulator, is firstly used to modulate the angular distribution of electron beam in the modulator. After passing through the special designed dispersion section, strong coherent micro-bunching is imprinted into the e beam which contains high-order harmonic components of the seed laser. The results verify the feasibility of this scheme for the generation of fully coherent radiation in EUV and soft X-ray regimes, which can be well interests of electron beams from a laser wakefield accelerator.