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We developed an optically synchronized highly stable frequency-doubled Nd:YAG laser with sub-nanosecond pulse duration. The 1064 nm seed pulses generated by soliton self-frequency shift in a photonic crystal fiber from Ti:sapphire oscillator pulses were stabilized by controlling input pulse polarization. The seed pulses were amplified to 200 mJ by diode-pumped amplifiers with a high stability of only

This article reports the development of a compact Thomson parabola spectrometer for laser-accelerated ions that can measure angular distribution with a high energy resolution and has a variable measurable energy range. The angular-resolved energy spectra for different ion species can be measured in a single shot, and the sampling angle can be selected from outside the vacuum region. The electric and magnetic fields are applied to the ion dispersion by using a permanent magnetic circuit and annulus sector-shaped electrodes with a wedge configuration. The compact magnetic circuit consists of permanent magnets, fixed yokes, and movable yokes. The magnetic flux is intentionally leaked to the movable yokes, allowing the magnetic field to be adjusted from 53 mT to 259 mT. The annulus sector-shaped electrodes with a wedge configuration provide better trace separation for high-energy ions, retain the lower-energy part of the ion signal, and subject ions passing through all pinholes to an equivalent Lorentz force. The magnetic and electric fields are designed for measuring protons and carbon ions with an energy range of 0.1–5 MeV. The spectrometer allows for the adjustment of the observable energy range afterward according to the parameters of the accelerated ion.

With the development Chirped Pulse Amplification (CPA) technique [1], ultra-short laser pulses with intensities over 1018 W/cm2 have been equipped in laboratories worldwide. By the incident of such intense laser pulses into underdense plasma, plasma waves with large amplitude will be stimulated in the wake of the drive laser. Electrons trapped in the wave can be accelerated to over GeV within a distance of centimeter scale. This compact laser wakefield acceleration (LWFA) [2] regime is considered to have great potentials in high energy physics and ultra-fast pump probe studies. However, due to the nonlinear interaction process between high power laser and plasma, the instability of the electron beams generated from LWFA is still an obstacle for application. To optimize the stability and beam parameters of laser wakefield accelerated electrons, single-shot beam diagnostic techniques need to be developed. Electron temporal distribution is one of the most important parameters in beam physics. The peak currents of electron bunches are partially determined by the bunch duration and related with the brightness of the electron beam. For the realization of a table-top x-ray free electron laser, this parameter plays an essential role. Yet, due to the noise of laser transmission light and fluctuations of generated electrons, single-shot non-destructive electron temporal diagnostics had been seldomly successfully conducted in LWFA. For this purpose, we for the first time introduced the electro-optic spatial decoding technique into LWFA research. In this talk, the recent development of this technique at Kansai Photon Science Institute (KPSI), National Institutes for Quantum and Radiological Science and Technology (QST) will be presented., レーザー学会第４１回学術講演会

レーザープラズマ粒子加速器の高繰り返し化はイオンや電子、X線など発生する高エネルギー量子ビームの高輝度化に直結することから、コンパクトな重粒子線ガン治療器をはじめとする広範な応用に大きく寄与する。また、機械振動に由来するレーザーパラメーターの揺らぎを能動的な制御を介することで大幅に抑制でき、量子ビームの安定性向上に寄与するメリットもある。しかし、この実現にはレーザー装置の高繰り返し化はもちろんのこと、ターゲット装置や評価装置でも同様の研究開発が必須となる。本講演では、レーザー駆動イオンビーム源開発としてターゲット・診断装置開発に平行し既存のテラワットレーザーを改造する形で進めている高繰り返しダブルCPAレーザーの開発の現状に関し特にフロントエンド部について報告する。, 第６７回応用物理学会春季学術講演会

In the presentation, we show the design and our approach to achieve soft X-ray free-electron lasers (FELs) by using staged laser plasma acceleration (LPA) of electrons.The staged LPA consists of several functionalized stages such as electron injector, phase rotation, and energy booster to manipulate electron beams to satisfy the requirements for an XFEL. This is a challenging task but this scheme has a favorable scaling to higher energies and has larger tuning knobs to manipulate electron beam quality., 11th International Conference on Inertial Fusion Sciences and Applications

MIRAレーザープラズマ加速器実証に向けた高コントラストレーザーのフロントエンド(1stCPA周り)の開発に関する発表, 平成３０年度レーザーとプラズマに関する研究会

The Compact Energy Recovery Linac (cERL) at KEK is a test accelerator in order to develop key components to realize remarkable ERL performance as a future light source. After the beam commissioning in December 2013, the legal current limit has been increased step-by-step like 1 uA, 10 uA, and 100 uA. Survey for the source of beam losses has been conducted in each step, and the study on beam dynamics and tuning has also been carried out. As a next step, 1 mA operation is scheduled in February 2016. In parallel to the increase in beam current, a laser Compton scattering (LCS) system which can provide high-flux X-ray to a beamline has been successfully commissioned. We report recent progress in various kinds of beam tuning: improvement of electron gun performance, high bunch charge operation, mitigation of beam losses, LCS optics tuning and bunch compression for THz radiation., The 7th International Particle Accelerator Conference (IPAC2016)

Detections of the pulse durations and arrival timings of relativistic electron beams are important issues for accelerators. Electro-optic diagnostics on the Coulomb fields of electron beams have the advantages of single shot and non-destructive characteristics.1,2 We present a study of introducing the electro-optic spatial decoding technique3 to laser wakefield acceleration (LWFA)4. To determine the time scale of the observed signal, a temporal mapping relationship is necessary. By placing an electro-optic crystal very close to a gas target, we discovered that the Coulomb field of the electron bunch possessed a spherical structure that was inconsistent with the previously widely used model. The field structure was demonstrated by experimental measurement, analytic calculations and simulations. A new temporal mapping relationship with generality was derived in a geometry where the signals had spherical wavefronts5. This study could be helpful for the applications of electro-optic diagnostics in laser plasma acceleration experiments. This work was funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan)., HEDS2018

In order to control the laser accelerated electron beam, the control of the plasma wave excited by a laser pulse is necessary. In order to control the plasma wave, the wave should be measured. As a first step of the control of the laser accelerated electron beam, we measure the plasma wave. By using two chirped probe pulses, frequency domain holographic (FDH) measurement is conducted. In the case of FDH, the spectrum can be converted to time. FDH is one of the single-shot plasma wave measurements. In order to produce the plasma wave, 10 TW and 30 fs laser pulse is focused onto a Helium gas jet. The two probe pulses are parallel to the main pulse. Without plasma wave, the interference fringes are straight lines. However, with plasma wave, the fringes are shifted. From the shift, the plasma density can be calculated. As a result, single-shot plasma wave measurement is succeeded., 光・量子ビーム科学合同シンポジウム2017

Laser wakefield acceleration (LWFA)1 has been studied intensively due to the inherent ultrashort bunch duration (fs) and large acceleration gradient (GV/cm) over conventional accelerators. This regime is considered promising on construction of compact table-top X-ray free electron lasers (XFEL)2. The generation of XFEL relies on the process of self-amplification of spontaneous emission (SASE)3, which requires electron beam with extremely high current and low emittance to cause micro-bunching. During LWFA experiment, it is essential to establish electron temporal profile diagnostics as a reference to laser plasma parameter adjustment for generation of high peak current electron beams. We present LWFA study via single-shot non-destructive electro-optic (EO) sampling4 technique for the first time. The electron spectra and divergence information had been detected simultaneously with electron bunch temporal signal. In the experiment, we observed earlier electron pulse arriving time with higher plasma density. At density above 3×1019cm-3, multi-bunch signal was frequently observed. PIC simulation has been performed to study the injection process. This diagnostic proved to have superior data attainability compared with previous works5-7 and could be introduced as a real time non-destructive electron pulse duration monitor for future LWFA experiment. \nThis work was funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan)., HEDS2017

application/pdf, We have investigated a technique for micromachining inorganic transparent materials. In the technique, patterning and coloration are performed by the direct irradiation of materials with pulsed laser soft x rays and the patterned areas are ablated using ultraviolet laser light. The technique utilizes the high precision of the soft x rays and the high energy density of conventional laser light. For demonstration, we irradiated quartz plates with Ta laser plasma soft x rays. This results in generation of transient surface opaque layers that absorb more than 40% of the 266 nm Nd:YAG laser light. Applying the technique, quartz plates are found to be ablated smoothly at 85 nm/shots.

Enhancement of the quality of laser wake-field accelerated (LWFA) electron beams implies the improvement and controllability of the properties of the wake waves generated by ultra-short pulse lasers in underdense plasmas. In this work we present a compendium of useful formulas giving relations between the laser and plasma target parameters allowing one to obtain basic dependences, e.g. the energy scaling of the electrons accelerated by the wake field excited in inhomogeneous media including multi-stage LWFA accelerators. Consideration of the effects of using the chirped laser pulse driver allows us to find the regimes where the chirp enhances the wake field amplitude. We present an analysis of the three-dimensional effects on the electron beam loading and on the unlimited LWFA acceleration in inhomogeneous plasmas. Using the conditions of electron trapping to the wake-field acceleration phase we analyse the multi-equal stage and multiuneven stage LWFA configurations. In the first configuration the energy of fast electrons is a linear function of the number of stages, and in the second case, the accelerated electron energy grows exponentially with the number of stages. The results of the two-dimensional particle-in-cell simulations presented here show the high quality electron acceleration in the triple stage injection–acceleration configuration.

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.