Discriminative detection of laser-accelerated multi-MeV carbon ions utilizing solid state nuclear track detectors

A new diagnosis method for the discriminative detection of laser‐accelerated multi‐MeV carbon ions from background oxygen ions utilizing solid‐state nuclear track detectors (SSNTDs) is proposed. The idea is to combine two kinds of SSNTDs having different track registration sensitivities: Bisphenol A polycarbonate detects carbon and the heavier ions, and polyethylene terephthalate detects oxygen and the heavier ions. The method is calibrated with mono‐energetic carbon and oxygen ion beams from the heavy ion accelerator. Based on the calibration data, the method is applied to identify carbon ions accelerated from multilayered graphene targets irradiated by a high‐power laser, where the generation of high‐energy high‐purity carbon ions is expected. It is found that 93 ± 1% of the accelerated heavy ions with energies larger than 14 MeV are carbons. The results thus obtained support that carbon‐rich heavy ion acceleration is achieved

Laser-driven multi-MeV high-purity proton acceleration via anisotropic ambipolar expansion of micron-scale hydrogen clusters

強力なレーザーを使ってエネルギーがそろった純度100％の陽子ビーム発生に成功 --レーザー駆動陽子ビーム加速器の実現へ向けて大きく前進--. 京都大学プレスリリース. 2022-10-13.Multi-MeV high-purity proton acceleration by using a hydrogen cluster target irradiated with repetitive, relativistic intensity laser pulses has been demonstrated. Statistical analysis of hundreds of data sets highlights the existence of markedly high energy protons produced from the laser-irradiated clusters with micron-scale diameters. The spatial distribution of the accelerated protons is found to be anisotropic, where the higher energy protons are preferentially accelerated along the laser propagation direction due to the relativistic effect. These features are supported by three-dimensional (3D) particle-in-cell (PIC) simulations, which show that directional, higher energy protons are generated via the anisotropic ambipolar expansion of the micron-scale clusters. The number of protons accelerating along the laser propagation direction is found to be as high as 1.6 ±0.3 × 10⁹/MeV/sr/shot with an energy of 2.8 ±1.9 MeV, indicating that laser-driven proton acceleration using the micron-scale hydrogen clusters is promising as a compact, repetitive, multi-MeV high-purity proton source for various applications

X-ray harmonic comb from relativistic electron spikes

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

Robustness of large‐area suspended graphene under interaction with intense laser

Graphene is known as an atomically thin, transparent, highly electrically and thermally conductive, light‐weight, and the strongest 2D material. We investigate disruptive application of graphene asa target of laser‐driven ion acceleration. We develop large‐area suspended graphene (LSG) and by transferring graphene layer by layer we control the thickness with precision down to a single atomic layer. Direct irradiations of the LSG targets generate MeV protons and carbons from sub‐relativistic to relativistic laser intensities from low contrast to high contrast conditions without plasma mirror, evidently showing the durability of graphene

Ultra-Intense, High Spatio-Temporal Quality Petawatt-Class Laser System and Applications

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

High-thermal-conductivity SiC ceramic mirror for high-average-power laser system

The importance of heat-resistant optics is increasing as the average power of high-intensity lasers increases. A silicon carbide (SiC) ceramic with high thermal conductivity is proposed as an optics substrate to suppress the thermal effect. The temperature rise of the substrate and the change in the surface accuracy of the mirror surface, which degrade the laser beam quality, are investigated. Gold mirrors on synthetic fused silica and SiC ceramic substrates are heated with a 532 nm wavelength laser diode. The synthetic fused silica substrate placed on an aluminum block shows a temperature increase by ~32 °C and a large temperature gradient. In contrast, the SiC ceramic substrate shows a uniform temperature distribution and a temperature increase by only ~4 °C with an absorbed power of ~2 W after 20 min laser irradiation. The surface accuracy (roughness) of the synthetic fused silica changes from /21.8 (29.0 nm) to /7.2 (88.0 nm), increasing by a factor of ~3.0 due to the expansion of the center. However, that of the SiC ceramic mirror changes from /21.0 (30.2 nm) to /13.3 (47.7 nm), increasing by a factor of ~1.6 while maintaining the same temperature distribution after laser irradiation

Recovery Dynamics of Semiconductor Saturable AAbsorber for Ultrafast High Intensity Lasers

超高強度レーザーシステムのための時間的なパルスクリーナーとしての過飽和吸収体、半導体ドープガラスの回復ダイナミクスを実験的に調べたので報告する。Optics & Photonics International Congress 2019 (The 8th Advanced Lasers and Photon Sources (ALPS2019)

Simple synchronization technique of a mode-locked laser for Laser-Compton scattering Gamma-ray source

We propose a simple and effective synchronization technique between a reference electrical oscillator and a mode-locked laser for a narrowband picosecond Laser-Compton scattering Gamma-ray source by using a commercial-based 1-chip frequency synthesizer, which is widely used in radio communication. The mode-locked laser has been successfully synchronized in time with a jitter of 180 fs RMS for 10 Hz - 100 kHz bandwidth. A good stability of 640 uHz at 80 MHz repetition rate for 10 hours operation has also been confirmed. We discuss in detail the design and performance of this technique (in terms of timing jitter, stability, and validity)