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A Neutron/Gamma-ray combined inspection system for hidden special nuclear materials (SNMs) in cargo containers has been developed under a program of Japan Science and Technology Agency in Japan. This inspection system consists of an active neutron-detection system for fast screening and a laser Compton backscattering gamma-ray source in coupling with nuclear resonance fluorescence (NRF) method for precise inspection. The inertial electrostatic confinement fusion device has been adopted as a neutron source and two neutron-detection methods, delayed neutron noise analysis method and high-energy neutron-detection method, have been developed to realize the fast screening system. The prototype system has been constructed and tested in the Reactor Research Institute, Kyoto University. For the generation of the laser Compton backscattering gamma-ray beam, a race track microtron accelerator has been used to reduce the size of the system. For the NRF measurement, an array of LaBr3(Ce) scintillation detectors has been adopted to realize a low-cost detection system. The prototype of the gamma-ray system has been demonstrated in the Kansai Photon Science Institute, National Institutes for Quantum and Radiological Science and Technology. By using numerical simulations based on the data taken from these prototype systems and the inspection-flow, the system designed by this program can detect 1 kg of highly enriched 235U (HEU) hidden in an empty 20-ft container within several minutes.

Non-destructive inspection carried out by using nuclear resonances excited by an MeV energy region gamma ray is a promising method. The high penetrability of MeV gamma ray of nuclear resonant energy makes possible the detection of nuclides surrounded by massive materials. As an application of this method, computed tomography imaging of nuclear distribution inside objects can be reconstructed from transmission factor of gamma rays. We have studied the image reconstruction of the nuclear distribution using Monte-Carlo simulations to estimate the gamma-ray transmission factor assuming the ELI-NP facility where about 3 order higher intensity of quasi-monoenergetic gamma rays will be available., CoE on Sustainable Energy System (Thai-Japan), Faculty of Engineering, Rajamangala University of Technology Thanyaburi (RMUTT), Thailand

The dependence of the nuclear resonance fluorescence (NRF) yield on the target thickness was studied. To this end, an NRF experiment was performed on 238U using a laser Compton back-scattering (LCS) γ-ray beam at the High Intensity γ-ray Source facility at Duke University. Various thicknesses of depleted uranium targets were irradiated by an LCS γ-ray beam with an incident beam energy of ∼2.475 MeV. The scattering NRF γ-rays were measured using an High-purity Germanium (HPGe) detector array positioned at scattering angles of 90° relative to the incident γ-beam. An analytical model for the NRF reaction yield (NRF RY model) is introduced to interpret the experimental data. Additionally, a Monte Carlo simulation using GEANT4 was performed to simulate the NRF interaction for a wide range of target thicknesses of the 238U. The measured NRF yield shows the saturation behavior. The results of both of the simulation and the analytical model can reproduce the saturation curve of the scattering NRF yield of 238U ag...

Computed Tomography (CT) using X-ray attenuation by atomic effects is now widely used for medical diagnosis and industrial non-destructive inspection. In this study, we performed a tomographic imaging of isotope (208Pb) distribution by the Nuclear Resonance Fluorescence (NRF), i.e. isotope specific resonant absorption and scattering of gamma rays, using Laser Compton Scattering (LCS) gamma rays. The NRF-CT image which includes both effects of atomic attenuation and nuclear resonant attenuation was obtained. By accounting for the atomic attenuation measured by a conventional method at the same time, a clear 208Pb isotope CT image was obtained. The contrast degradation due to notch refilling caused by small-angle Compton scattering is discussed. This study clearly demonstrates the capability of the isotope-specific CT imaging based on nuclear resonant attenuation which will be a realistic technique when the next generation of extremely intense LCS gamma-ray sources will be available. The expected image acquisition time using these intense LCS gamma rays was discussed.

This paper reviews techniques for improving the temporal contrast and spatial beam quality in an ultra-intense laser system that is based on chirped-pulse amplification (CPA). We describe the design, performance, and characterization of our laser system, which has the potential for achieving a peak power of 600 TW. We also describe applications of the laser system in the relativistically dominant regime of laser-matter interactions and discuss a compact, high efficiency diode-pumped laser system.

The authors have demonstrated an optical parametric chirped-pulse amplification (OPCPA)/Yb:YAG ceramic thin disk hybrid laser system having hundred mJ level pulse energy sub-picosecond pulse duration with high temporal contrast. At an input chirped-pulse energy of 3.8 mJ from an OPCPA preamplifier an output energy of 130 mJ has been generated from multipass diode-pumped Yb:YAG ceramic thin disk amplifier. A recompressed pulse duration of 450 fs with a contrast level of less than 7.2×10−9 at −150 ps before the main pulse has been obtained. The contrast level is the highest value achieved in Yb:YAG chirped-pulse amplification (CPA) laser system at 100 mJ level.

At the Kansai Photon Science Institute of the Japan Atomic Energy Agency, we have developed a Compton backscattered X-ray source in the energy region of a few hundred keV. The X-ray source consists of a 150-MeV electron beam, with a pulse duration of 10 ps (rms), accelerated by a Microtron accelerator and an Nd:YAG laser, with a pulse duration of 10 ns (FWHM). In the first trial experiment, the X-ray flux is estimated to be (2.2±1.0)×10 2 photons/pulse. For the actual application of an X-ray source, it is important to increase the generated X-ray flux as much as possible. Thus, for the purpose of increasing the X-ray flux, we have developed the pulse compression system for the Nd:YAG laser via stimulated Brillouin scattering (SBS). The SBS pulse compression has the great advantages of a high conversion efficiency and a simple structure. In this article, we review the present status of the Compton backscattered X-ray source and describe the SBS pulse compression system.

We report the highest energy broadband laser pulses at a center wavelength of 1030 nm based on optical parametric chirped-pulse amplification (OPCPA). We have demonstrated amplification of 1030 nm femtosecond laser pulses from a broadband Yb oscillator to over 6.5 mJ with a total gain of greater than 107 achieved in a single pass through only 56 mm of gain material at a 10 Hz repetition rate. The amplified spectral bandwidth of 10.8 nm affords recompression to a 230 fs pulse duration following amplification. As an alternative to the regenerative amplifier (RA) this system is one of the more promising candidates for realizing compact, high intensity, direct diode-pumped, high repetition rate femtosecond Yb:YAG chirped-pulse amplification (CPA) in laser systems.

We present the results of experiments on the generation of both high and low frequency electromagnetic radiation from the nonlinear interaction of intense laser beams with underdense plasmas. High frequency radiation is generated as a result of the reflection of a near-infrared laser beam by breaking plasma waves. In the proof-of-principle experiment, a 2 TW, 76 fs Ti:sapphire laser pulse was focused to generate wake waves, and a ~0.1 TW laser pulse was focused to collide with the electron density modulations. Frequencies of the reflected light were 56–110 times higher than that of the initial laser. The estimated number of photons per solid angle was 3×107 photons/sr. Low frequency radiation is emitted by the plasma as well. We found that the polarization of the radiation was similar to that of the driver laser. These properties are in accordance with the generation mechanism by relativistic solitons.

We demonstrate a high-contrast, high-intensity double chirped-pulse amplification (CPA) Ti:sapphire laser system using an optical parametric chirped-pulse (OPCPA) pre- amplifier. By injecting cleaned microjoule seed pulses into the OPCPA, a temporal contrast greater than 10 10 within picosecond times before the main femtosecond pulse is demonstrated with an output pulse energy of 1.7 J and a pulse duration of 30 fs, corresponding to a peak power of 60 TW at a 10 Hz repetition rate. This system uses a cryogenically-cooled Ti:sapphire final amplifier and generates focused peak intensities in excess of 10 20 W/cm 2 .

We demonstrate a highly reproducible acceleration of a high-quality electron bunch injected into the laser wake field accelerator with the help of a countercrossing laser pulse. In our experiments, the wake field is generated by a subrelativistic laser pulse; the second laser pulse collides with the first pulse at 135 , realizing optical injection of electron bunch into the wake field. Because the second pulse is countercrossing, it cannot damage the laser system. The observed electron bunch has the energy of 14 MeV with an 11% (1.5 MeV) spread, the total charge of 22 pC, and a reproducibility of at least 50%.

We have observed simultaneously both the fast proton generation and terahertz (THz) radiation in the laser pulse interaction with a 5-μm thick titanium target. In order to control the proton acceleration and THz radiation, we have changed the duration of the amplified spontaneous emission (ASE) preceding the main pulse generated by the high-intensity Ti:sapphire laser. A fast proton beam with the maximal energy of ∼ 490 keV has been realized by reducing the duration of the ASE. Simultaneously, an intense emission of THz radiation is observed for various ASE durations. We propose the antenna mechanism for the THz radiation, according to which the fast electrons moving along the target surface emit the low-frequency electromagnetic wave.

An active non-destructive detection system for special nuclear materials (SNMs) such as 235U has been developed for container inspection at sea ports. The SNMs can be detected by using nuclear resonance fluorescence (NRF) with a quasimonochromatic gamma-ray beam provided from a laser Compton Scattering (LCS) source. We have studied the optimum geometry for the detector array by Monte Carlo simulation code, GEANT4, which has been modified to take into account all physical processes in NRF. The simulation code has been checked by the experimental data taken in New-SUBARU and HIgS facility. NRF yield at different scattering angles were examined with different thickness of 235U target. The result shows that the backward angle is the optimum geometry for NRF detection in terms of NRF yield and S/N ratio caused by atomic scattering. Realistic simulation for a container cargo has been performed. Detector array of 100 LaBr 3 (Ce) detectors has been examined with 3 different size of crystals. Consequently, we can demonstrate the ability of the proposed inspection system.

The results of experiments are presented for a single laser pulse interaction with a very low density gas target under conditions when the generated wake wave is below the wave-breaking threshold and the laser pulse power is lower than the critical power for relativistic self-focusing. A quasimonoenergetic electron beam is found to be stably generated for various laser pulse intensity values by controlling the acceleration length.

X-ray devices are far superior to optical ones for providing nanometre spatial and attosecond temporal resolutions. Such resolution is indispensable in biology, medicine, physics, material sciences, and their applications. A bright ultrafast coherent X-ray source is highly desirable, for example, for the diffractive imaging of individual large molecules, viruses, or cells. Here we demonstrate experimentally a new compact X-ray source involving high-order harmonics produced by a relativistic-irradiance femtosecond laser in a gas target. In our first implementation using a 9 Terawatt laser, coherent soft X-rays are emitted with a comb-like spectrum reaching the 'water window' range. The generation mechanism is robust being based on phenomena inherent in relativistic laser plasmas: self-focusing, nonlinear wave generation accompanied by electron density singularities, and collective radiation by a compact electric charge. The formation of singularities (electron density spikes) is described by the elegant mathematical catastrophe theory, which explains sudden changes in various complex systems, from physics to social sciences. The new X-ray source has advantageous scalings, as the maximum harmonic order is proportional to the cube of the laser amplitude enhanced by relativistic self-focusing in plasma. This allows straightforward extension of the coherent X-ray generation to the keV and tens of keV spectral regions. The implemented X-ray source is remarkably easily accessible: the requirements for the laser can be met in a university-scale laboratory, the gas jet is a replenishable debris-free target, and the harmonics emanate directly from the gas jet without additional devices. Our results open the way to a compact coherent ultrashort brilliant X-ray source with single shot and high-repetition rate capabilities, suitable for numerous applications and diagnostics in many research fields.

We have demonstrated efficient frequency doubling of high-energy fundamental Nd:YAG laser pulse energy of the multi-joule (J) level at a high repetition rate using high optical-quality top-seeded solution growth CsB3O5(TSSG-CBO) crystal for the first time. Second-harmonic (532 nm) generation (SHG) output energy of 1.2 J at 10 Hz is obtained with a conversion efficiency of 60%. This result has been obtained at the multi-J level by the growth of high optical-quality TSSG-CBO crystal with the large effective nonlinear coefficient and high damage threshold. These results indicate that TSSG-CBO is a good candidate material for high-energy SHG of Nd-doped lasers at the several J level or more with high repetition rate.

A LaBr3(Ce) detector array has been constructed for the non-destructive inspection of special nuclear materials (SNMs) using the nuclear resonance fluorescence (NRF) technique. The fundamental performance of the LaBr3(Ce) detector array, the proper data acquisition system and the analysis system are demonstrated. The developed LaBr3(Ce) array is shown to have a good energy resolution and an excellent energy linearity. The feasibility of using the LaBr3(Ce) array for the inspection system has been investigated by measuring the NRF integrated cross section for exciting the 1.73 MeV state in 235U.

The optimum geometric configuration of the detector system for non-destructive assay (NDA) of special nuclear material (SNM) by using nuclear resonance fluorescence (NRF) measurements has been studied. A Monte Carlo radiation transport code, GEANT4, has been developed to calculate NRF interaction, as well the simulation performed for detector array consist of seven LaBr 3 :Ce (1.5″ × 3″) detectors positioned at 5 cm from the center of the target by stepping angle 45°, to study the optimum scattering angle of NRF γ-rays with respect to the incoherent scattering and the self-absorption of target material. The 235U isotope used as target with different thicknesses at the resonant energy level 1733 keV. The calculation results addressed that, the measurements of NRF γ-rays at backward angles - relative to interrogating γ-beam is the optimum geometric configuration system of detectors.

A nuclear resonance fluorescence (NRF) experiment was performed on a 235U target with the quasi-monochromatic γ-ray at High Intensity γ-ray Source (HIγS) using the 1733 keV resonant energy. A LaBr3(Ce) detector array consisting of 8 cylindrical detectors, each has length of 7.62 cm and a diameter of 3.81 cm, in diameter was implemented in this measurement. Moreover, high purity germanium (HPGe) detector array consisting of 4 detectors each has a relative efficiency of 60 %, was used as a benchmark for the measurement taken by LaBr3(Ce) detector array. The integrated cross-section of the NRF level measured with LaBr3(Ce) detector showed good agreement with the available data. Consequently, LaBr3(Ce) detector could be feasible to use as a detector for the special nuclear material inspection system.

The Nuclear Physics oriented pillar of the pan-European Extreme Light Infrastructure (ELI-NP) will host an ultra-bright, energy tunable, and quasi-monochromatic gamma-ray beam system in the range of 0.2–19.5 MeV produced by laser Compton backscattering. This gamma beam satisfies the criteria for large-size product investigations with added capabilities like isotope detection through the use of nuclear resonance fluorescence (NRF) and is ideal for non-destructive testing applications. Two major applications of gamma beams are being envisaged at ELI-NP: industrial applications based on NRF and industrial radiography and tomography. Both applications exploit the unique characteristics of the gamma beam to deliver new opportunities for the industry. Here, we present the experimental setups proposed at ELI-NP and discuss their performance based on analytical calculations and GEANT4 numerical simulations. One of the main advantages of using the gamma beam at ELI-NP for applications based on NRF is the availability of an advanced detector array, which can enhance the advantages already provided by the high quality of the gamma beam.

We report on novel methods to generate ultra-short, coherent, X-rays using a laserplasma interaction. Nonlinear interaction of intense laser pulses with plasma creates stable, specific structures such as electron cusps. For example, wake waves excited in an underdense plasma by an intense, short-pulse laser become dense and propagate along with the laser pulse. This is called a relativistic flying mirror. The flying mirror can reflect a counter-propagating laser pulse and directly convert it into high-frequency radiation, with a frequency multiplication factor of ∼ 4γ2 and pulse shortening with the same factor. After the proof-of-principle experiments, we observed that the photon number generated in the flying mirror is close to the theoretical estimate. We present the details of the experiment in which a 9 TW laser pulse focused into a He gas jet generated the Flying Mirror, which partly reflected a 1 TW pulse, giving up to ∼ 1010 photons, 60 nJ (1.4×1012 photons/sr) in the XUV spectral region (12.8-22 nm).

We demonstrate a new high-order harmonic generation mechanism reaching the "water window" spectral region in experiments with multiterawatt femtosecond lasers irradiating gas jets. A few hundred harmonic orders are resolved, giving mu J/sr pulses. Harmonics are collectively emitted by an oscillating electron spike formed at the joint of the boundaries of a cavity and bow wave created by a relativistically self-focusing laser in underdense plasma. The spike sharpness and stability are explained by catastrophe theory. The mechanism is corroborated by particle-in-cell simulations.

We propose a new mechanism of high-order harmonic generation during an interaction of a high-intensity laser pulse with underdense plasma. A tightly focused laser pulse creates a cavity in plasma pushing electrons aside and exciting the wake wave and the bow wave. At the joint of the cavity wall and the bow wave boundary, an annular spike of electron density is formed. This spike surrounds the cavity and moves together with the laser pulse. Collective motion of electrons in the spike driven by the laser field generates high-order harmonics. A strong localization of the electron spike, its robustness to oscillations imposed by the laser field and, consequently, its ability to produce high-order harmonics is explained by catastrophe theory. The proposed mechanism explains the experimental observations of high-order harmonics with the 9 TW J-KAREN laser (JAEA, Japan) and the 120 TW Astra Gemini laser (CLF RAL, UK) [A. S. Pirozhkov, et al., arXiv:1004.4514 (2010); A. S. Pirozhkov et al, AIP Proceedings, this volume]. The theory is corroborated by high-resolution two-and three-dimensional particle-in-cell simulations.

Yb:YAG CPA have a potential to develop a compact, high peak power at high repetition rates. For high energy pulses of short duration Yb:YAG regenerative amplifiers have mainly been studied for which significant prepulse and amplified spontaneous emission (ASE). In laser proton acceleration studies it is very important to suppress the prepulse and ASE levels, because a preplasma is generated before the peak of the laser pulse, therefore the maximum proton energy is limited. To overcome this problem, the OPCPA can efficiently provide high gain for the main pulse while suppressing prepulse amplification. Here we have first demonstrated a hundred mJ level, femtosecond of an OPCPA/Yb:YAG hybrid laser system with a contrast level of 10−9 at −150 ps.

A laser-driven repetition-rated 1.9 MeV proton beam line composed of permanent quadrupole magnets (PMQs), a radio frequency (rf) phase rotation cavity, and a tunable monochromator is developed to evaluate and to test the simulation of laser-accelerated proton beam transport through an integrated system for the first time. In addition, the proton spectral modulation and focusing behavior of the rf phase rotation cavity device is monitored with input from a PMQ triplet. In the 1.9 MeV region we observe very weak proton defocusing by the phase rotation cavity. The final transmitted bunch duration and transverse profile are well predicted by the PARMILA particle transport code. The transmitted proton beam duration of 6 ns corresponds to an energy spread near 5% for which the transport efficiency is simulated to be 10%. The predictive capability of PARMILA suggests that it can be useful in the design of future higher energy transport beam lines as part of an integrated laser-driven ion accelerator system.

We have developed a femtosecond high-intensity laser system that combines both Ti:sapphire chirped-pulse amplification (CPA) and optical parametric CPA (OPCPA) techniques and produces more than 30 J broadband output energy, indicating the potential for achieving peak powers in excess of 500 TW. With a cleaned high-energy seeded OPCPA preamplifier as a front end in the system, for the compressed pulse without pumping the final amplifier, we found that the temporal contrast in this system exceeds 10(10) on the subnanosecond time scales, and is near 10(12) on the nanosecond time scale prior to the peak of the main femtosecond pulse. Using diffractive optical elements for beam homogenization of a 100 J level high-energy Nd:glass green pump laser in a Ti:sapphire final amplifier, we have successfully generated broadband high-energy output with a near-perfect top-hat-like intensity distribution.

We report the demonstration of over 30-J of uncompressed broadband energy, indicating the potential peak power in excess of 500-TW with high temporal-contrast around 1011 and a flat-toped spatial-profile with an ∼80 % filling factor.

Frequency doubling of high-energy Nd-doped laser emission yields harmonically converted laser energy (532-nm) of 1.2-J with 60 % conversion efficiency using a high optical quality top-seeded solution growth CsB 3 O 5 crystal.

The broad absorption bandwidth of ytterbium (Yb) is well-suited to laser diode pumping at 940 nm. Because Yb is known for its low quantum defect, thermal loading is significantly reduced. Consequently, Yb doped crystals, especially Yb:YAG, show promise for developing compact, high peak power laser systems at high repetition rates. For high energy pulses of short duration Yb:YAG regenerative amplifiers have mainly been studied where the generation of significant prepulse and amplified spontaneous emission (ASE) is known. At higher intensities (for example ∼ 1018Wcm−2 and beyond) laser-matter interactions can require suppression of prepulse and ASE intensity in order to maintain or control the target state that a short or ultrashort main pulse would irradiate. In many cases it is therefore critical to avoid significant preplasma formation. To solve these problem, the optical parametric chirped pulse amplification (OPCPA) can efficiently provide high gain of the main pulse while suppressing prepulse amplification and reducing gain narrowing of the spectrum. We present in this conference the first Yb femtosecond oscillator based OPCPA demonstration at 1030 nm and with spectral bandwidth adequate for amplifying femtosecond pulses. Direct laser diode (LD) amplification of 1030 nm light makes this OPCPA a feasible preamplifier for a compact, high contrast, energetic, short pulse laser systems that can be considered for development of laser-driven proton accelerators.

Electromagnetic wave generation in the extreme ultraviolet (XUV) and infrared (IR) wavelength range occurs during the interaction of intense short laser pulses with underdense plasmas. XUV pulses are generated through laser light reflection from relativistically moving electron dense shells (flying mirrors). A proof-of-principle and an advanced experiment on flying mirrors are presented. Both of the experiments demonstrated light reflection and frequency upshift to the XUV wavelength range (14-20 nm). The advanced experiment with a head-on collision of two laser pulses exhibited the high reflected photon number. IR radiation, which is observed in the forward direction, has the wavelength of 5 μm and dominantly the same polarization as the driving laser. The source of the IR radiation is attributed to emission from relativistic solitons formed in the underdense plasma.

A strongly nonlinear wake wave driven by an intense laser pulse can act as a partially reflecting relativistic mirror (the flying mirror) [S. V. Bulanov, et al., Bulletin of the Lebedev Physics Institute, No. 6, 9 (1991); S. V. Bulanov, et al., Phys. Rev. Lett. 91, 085001 (2003)]. Upon reflection from such mirror, a counter‐propagating optical‐frequency laser pulse is directly converted into high‐frequency radiation, with a frequency multiplication factor ∼4γ2 (the double Doppler effect). We present the results of recent experiment in which the photon number in the reflected radiation was at least several thousand times larger than in our proof‐of‐principle experiment [M. Kando, et al., Phys. Rev. Lett. 99, 135001 (2007); A. S. Pirozhkov, et al., Phys. Plasmas 14, 123106 (2007)]. The flying mirror holds promise of generating intense coherent ultrashort XUV and x‐ray pulses that inherit their temporal shape and polarization from the original optical‐frequency (laser) pulses. Furthermore, the reflected radi...

When an intense short laser pulse interacts with plasmas, the nonlinear interaction causes various phenomena such as high energy particle generation, strong radiation in the x‐ray to THz frequency range. Formation of solitons is one of these interesting topics and has been studied mainly from theoretical aspects. Solitons are formed in an underdense plasma in the process of the laser pulse frequency downshift. They store a portion of the EM wave energy with the polarization inherited from the laser pulse‐driver and emit it at the plasma‐vacuum interface in the form of low frequency EM bursts. Solitons were observed experimentally by proton‐beam imaging and in the visible‐near‐infrared emissions from the plasma. A low frequency EM radiation emission has also been observed in our experiments. The interpretation invokes the relativistic electromagnetic solitons. We present the results of the polarization‐resolved measurements of low frequency radiation from the plasma region irradiated by the intense laser pulse. A dominant component of the observed THz radiation has the same polarization as the driver laser pulse.

We demonstrate the generation of greater than 1010 temporal contrast with over 1020 W/cm2 peak intensity pulses at a 10 Hz repetition rate from a Ti:sapphire chirped‐pulse amplification (CPA) laser system utilizing double CPA, optical parametric chirped‐pulse amplification (OPCPA), and cryogenic‐cooling techniques. We also successfully produce uncompressed output pulse energy exceeding 30 J, indicating potential for peak power at the 500 TW level.

The authors describe firstly the lasers for high intensity physics experiments at JAEA including J-KAREN and JLITE-X lasers which can deliver 00TW and 0TW laser power, respectively. Secondly the authors describe demonstration of flying mirror technique which will become a new technique to make a coherent tunable x-ray source. Thirdly a femto-second laser driven incoherent soft x-ray source and its imaging applications for nano-structures are described. The th topic includes femto-second laser driven multiple quantum beam generation and its applications using a laser driven thin foil target.

Reported in this article is the generation of unique polarized x-rays in the sub-MeV region by means of the Thomson backscattering of the Nd:YAG laser photon with a wavelength of 1064 nm on the 150 MeV electron from the microtron accelerator. The maximum energy of the x-ray photons is estimated to be about 400 keV. The total energy of the backscattered x-ray pulse is measured with an imaging plate and a LYSO scintillator. The angular divergence of the x-rays is also measured by using the imaging plate. We confirm that the x-ray beam is polarized according to the laser polarization direction with the Compton scattering method. In addition, we demonstrate the imaging of the object shielded by lead with the generated x-rays.

We report the first high-contrast, high-intense Ti:sapphire chirped-pulse amplification laser system incorporating a nonlinear pre-amplifier based on an optical parametric chirped-pulse amplification for use in experiments where relativistic effects dominate the physics.

We demonstrate a high‐contrast, 80‐TW, 19‐fs Ti:sapphire chirped‐pulse amplification laser system that incorporates a nonlinear pre‐amplifier based on optical parametric chirped‐pulse amplifier (OPCPA) for use in experiments where relativistic effects dominate the physics. With the OPCPA, the background temporal contrast is significantly improved to ∼10−9 in a few picoseconds interval prior to the main laser pulse. By cooling the Ti:sapphire crystal in the final amplifier down to 77 K, the chirped‐pulses are amplified to 2.9 J at 10 Hz repetition rate without thermal lensing effect.

In a plasma wake wave generated by a high power laser, modulations of the electron density take the shape of paraboloidal dense shells, moving almost at the speed of light. A counterpropagating laser pulse is partially reflected from the shells, acting as relativistic flying mirrors, producing a time-compressed frequency-multiplied pulse due to the double Doppler effect. The counterpropagating laser pulse reflection from the plasma wake wave accompanied by its frequency multiplication (with a factor from 50 to 114) was detected in our experiment.

Projection images of a metal mesh produced by directional MeV electron beam together with directional proton beam, emitted simultaneously from a thin foil target irradiated by an ultrashort intense laser, are recorded on an imaging plate for the electron imaging and on a CR-39 nuclear track detector for the proton imaging. The directional electron beam means the portion of the electron beam which is emitted along the same direction (i.e., target normal direction) as the proton beam. The mesh patterns are projected to each detector by the electron beam and the proton beam originated from tiny virtual sources of ~20 µm and ~10 µm diameters, respectively. Based on the observed quality and magnification of the projection images, we estimate sizes and locations of the virtual sources for both beams and characterize their directionalities. To carry out physical interpretation of the directional electron beam qualitatively, we perform 2D particle-in-cell simulation which reproduces a directional escaping electron component, together with a non-directional dragged-back electron component, the latter mainly contributes to building a sheath electric field for proton acceleration. The experimental and simulation results reveal various possible applications of the simultaneous, synchronized electron and proton sources to radiography and pump-probe measurements with temporal resolution of ~ps and spatial resolution of a few tens of µm.

The laser contrast ratio within picosecond timescales is one of the important parameters for laser acceleration. For a high laser contrast ratio, a 140 MeV monoenergetic electron beam with a charge of 44 pC is obtained by using a 20 TW Ti:sapphire laser. For a low laser contrast ratio, a low quality electron beam or no electron beam is generated, because the pre-pulse blows out plasma electrons and puts the plasma into disorder before the main pulse interacts with the plasma. The laser contrast ratio should be high enough in order to generate a high quality electron beam with a large amount of charge.

Optical parametric chirped-pulse amplification (OPCPA) operation with low gain by seeding with high-energy, clean pulses is shown to significantly improve the contrast to better than 10(-10) to 10(-11) in a high-intensity Ti:sapphire laser system that is based on chirped-pulse amplification. In addition to the high-contrast broadband, high-energy output from the final amplifier is achieved with a flat-topped spatial profile of filling factor near 77%. This is the result of pump beam spatial profile homogenization with diffractive optical elements. Final pulse energies exceed 30 J, indicating capability for reaching peak powers in excess of 500 TW.

A new observation method of providing a precise collision of two full-power counter-propagating laser pulses is proposed and demonstrated. The method is a combination of top-view imaging, side-view shadowgram, extra-ultraviolet (XUV) spectrograph, and returning pulse monitoring. This allows us to align two counter-propagating laser pulses at their colliding point in a real situation (full power laser operation in plasma). The achieved spatial resolution of the monitor in the plasma is 1.35 µm with the precision level of alignment better than 15 µm even when there is plasma present.

The results of experiments are presented for the laser electron acceleration in the ablative capillary discharge plasma. The plasma channel is formed by the discharge inside the ablative capillary. The intense short laser pulse is guided over a 4 cm length. The generated relativistic electrons show both the quasimonoenergetic and quasi-Maxwellian energy spectra, depending on laser and plasma parameters. The analysis of the inner walls of the capillaries that underwent several tens of shots shows that the wall deformation and blistering resulted from the discharge and laser pulse effects.

Using three different laser systems, we demonstrate a convenient and simple plasma based diagnostic of the contrast of high-power short-pulse lasers. The technique is based on measuring the specular reflectivity from a solid target. The reflectivity remains high even at relativistic intensities above 10(19) W/cm(2) in the case of a high-contrast prepulse-free laser. On the contrary, the specular reflectivity drops with increasing intensities in the case of systems with insufficient contrast due to beam breakup and increased absorption caused by preplasma.