Search

Beam charge control in the staging of laser wakefield acceleration (LWFA) is a crucial technique for developing full-optical jitter-free high-energy electron accelerators. Precise control of total charge in pre-accelerated electron bunches is necessary to achieve practical electron beam characteristics in the final acceleration stage(s). In contrast to the well-known cathode techniques in conventional accelerators, in LWFA the electron injection results from non-linear processes originating from plasma wave breaking. Therefore, the development of charge control requires a deep understanding of the electron self-injection processes and applications of non-trivial tools. The use of asymmetric gas-jet nozzles seems to be a promising way in developing charge control via tuning the target parameters such as plasma density, density slope, and acceleration length. Here, we demonstrate and characterize controllable electron self-injection, owing to a parametric resonance in slantwise density gas jets irradiated by 50 TW femtosecond laser pulses. The measured characteristics of the electron bunches, in which charge and energy distribution depend on the gas density and gas density gradient, agree well with those obtained by multidimensional particle-in-cell simulation and confirm the possibility of charge control.

We report on the design and characterization of the plasma mirror system installed on the J-KAREN-P laser at the Kansai Photon Science Institute, National Institutes for Quantum Science and Technology. The reflectivity of the single plasma mirror system exceeded 80%. In addition, the temporal contrast was improved by two orders of magnitude at 1 ps before the main pulse. Furthermore, the laser near-field spatial distribution after the plasma mirror was kept constant at plasma mirror fluence of less than 100 kJ/cm2. We also present the results of investigating the difference and the fluctuation in energy, pulse width and pointing stability with and without the plasma mirror system.

筆頭筆者らは、2017 年にらせん波面を形成するガンマ線が非線形逆トムソン散乱によって発生できることを理論的に示した。通常の逆トムソン散乱は、高エネルギー電子によるレーザー光子の散乱によってガンマ線が発生する過程である。ここで、ピークパワーがテラ~ペタワット級の高強度レーザーを使用すると高次高調波ガンマ線が発生し、n 次の高調波は1次ガンマ線に対してn倍のエネルギーを持つ。発生する光の電場には位相項 exp{i(n-1)φ}が含まれ、2次以上の高次高調波が(n-1)ħのOAM を運ぶ。 現在、量研機構の関西光科学研究所において非線形逆トムソン散乱によるガンマ線渦発生に関する研究を進めている。本年会ではその内容について発表する。, 日本物理学会第76回年次大会

In Japan we are conducting a laser-plasma acceleration (LPA) project aiming a compact X-ray free-electron laser (XFEL) system and a compact carbon ion injector for cancer therapy including efficient laser driver development. In this talk we will focus on the laser electron acceleration part. Our LPA electron beam platform is located in the SPring-8 Center site at RIKEN, Japan, where the prototype XFEL of SACLA was tested. In the platform a Ti:sapphire laser system is installed and it can deliver three synchronized laser pulses (~20 – 30 fs) with pulse energies of 1 J, 2 J, and 10 J. Our strategy is staged electron acceleration using these pulses by manipulating electron phase space to obtain monoenergetic electron beams. In this talk we present our recent results on ~250 MeV, reproducible, quasi-monoenergetic electron production, undulator radiation test, etc. *This work was supported by JST-Mirai Program Grant Number JPMJMI17A1, Japan., IAS Program on High Energy Physics (HEP 2021)

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 low-lying dipole strength in $^{52}\mathrm{Cr}$ was measured in nuclear resonance fluorescence experiments using a quasimonochromatic, linearly polarized photon beam. The parities of the excited dipole states were determined by the intensity asymmetry of resonantly scattered $\ensuremath{\gamma}$ rays with respect to the polarization plane of the incident photon beam. We observed 62 resonances at excitation energies between 7.5 and 12.1 MeV. The observed $M1$ and $E1$ strengths were compared via random-phase-approximation calculations using the Skyrme interaction. The effects of two-particle--two-hole configuration mixing and tensor force on dipole strength distributions were investigated.

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.

The performance of LaBr 3 (Ce) to measure nuclear resonance fluorescence (NRF) excitations is discussed in terms of limits of detection and in comparison with high-purity germanium (HPGe) detectors near the 2 MeV region where many NRF excitation levels from special nuclear materials are located. The NRF experiment was performed at the High Intensity γ-ray Source (HIγS) facility. The incident γ-rays, of 2.12 MeV energy, hit a B 4 C target to excite the 11 B nuclei to the first excitation level. The statistical-sensitive non-linear peak clipping (SNIP) algorithm was implemented to eliminate the background and enhance the limits of detection for the spectra measured with LaBr 3 (Ce). Both detection and determination limits were deduced from the experimental data.

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.

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.

Lanthanum halide scintillator LaBr3(Ce) could potentially improve the performance of spectroscopic systems because of their fine energy resolution in comparison with traditional scintillator materials and a good linearity of the energy response. Monte Carlo simulation of a detector response function presents a very challenging problem especially in 2 MeV region where internal radioisotopes inside the LaBr3(Ce) crystal make the energy response complex structure. The detector response functions of LaBr3(Ce) (38.1 mm × 76.2 mm cylindrical) have been calculated for standard γ-ray sources and internal sources using simulation toolkit GEANT4. The internal activity was investigated in details by comparison simulation results with the experimental. As a result we can reproduce the experimental spectra, however, there is still a few missing sources around 2 MeV region.

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.

A study of a non-destructive inspection system for hidden special nuclear materials in the cargo container at the sea port has been carried out under a promotion of Japan Science and Technology. This inspection system consists of an active neutron detection method for a fast screening purpose and a nuclear resonance fluorescence (NRF) method for isotope identification. The inertial electrostatic confinement fusion device has been developed for a neutron source and two neutron detection methods, the Feynman-alpha method and high energy neutron detection method, have been examined to realize the fast screening system. Generation of a quasi-monochromatic gamma-ray beam from the laser Compton Backscattering by using a compact microtron electron accelerator and an NRF experiment on uranium target using a new type of scintillation detector, LaBr3(Ce), has been studied to realize the isotope identification system.

Excitations in 235U were measured with LaBr3:Ce scintillation detectors using the nuclear resonance fluorescence (NRF) technique. A NRF experiment was performed at the High Intensity y-ray Source (HIyS) facility using quasi-monochromatic circularly or linearly polarized y-ray beams. Photons scattered at 90· relative to the incident beam were detected with two different sizes of cylindrical LaBr3:Ce detectors. Clear NRF peaks at 1733 and 1815 keY corresponding to de-excitations to the ground state and/or low-lying levels in 235U were observed within 77 minutes of beam time even under the high background due to the selfactivity of LaBr3:Ce and the radioactive decay of 214Bi nuclei existing in the 235U target. The present study shows a possibility of using LaBr3:Ce detector to perform NRF experiments, promoting many options for inspection of special nuclear materials.

We experimentally demonstrate a new regime of high-order harmonic generation by relativistic-irradiance lasers in gas jet targets. Bright harmonics with both odd and even orders, generated by linearly as well as circularly polarized pulses, are emitted in the forward direction, while the base harmonic frequency is downshifted. A 9 TW laser generates harmonics up to 360 eV, within the 'water window' spectral region. With a 120 TW laser producing 40 uJ/sr per harmonic at 120 eV, we demonstrate the photon number scalability. The observed harmonics cannot be explained by previously suggested scenarios. A novel high-order harmonics generation mechanism [T. Zh. Esirkepov et al., AIP Proceedings, this volume], which explains our experimental findings, is based on the phenomena inherent in the relativistic laser - underdense plasma interactions (self-focusing, cavity evacuation, and bow wave generation), mathematical catastrophe theory which explains formation of electron density singularities (cusps), and collective radiation due to nonlinear oscillations of a compact charge.

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.

Laser light reflection by a relativistically moving electron density modulation (flying mirror) in a wake wave generated in a plasma by a high intensity laser pulse is investigated experimentally. A counterpropagating laser pulse is reflected and upshifted in frequency with a multiplication factor of 37--66, corresponding to the extreme ultraviolet wavelength. The demonstrated flying mirror reflectivity (from $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ to $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$, and from $1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ to $0.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, for the photon number and pulse energy, respectively) is close to the theoretical estimate for the parameters of the experiment.

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...