In this work, we present a novel, to the best of our knowledge, and practical method for generating optical vortices in high-power laser systems. Off-axis spiral phase mirrors are used at oblique angles of incidence in the beam path after amplification and compression, allowing for the generation of high-power optical vortices in almost any laser system. An off-axis configuration is possible via modification of the azimuthal gradient of the spiral phase helix and is demonstrated with a simple model using a discrete spiral staircase. This work presents the design, fabrication, and implementation of off-axis spiral phase mirrors in both low- and high-power laser systems.

The Centro de Laseres Pulsados in Salamanca, Spain has recently started operation phase and the first user access period on the 6 J 30 fs 200 TW system (VEGA 2) already started at the beginning of 2018. In this paper we report on two commissioning experiments recently performed on the VEGA 2 system in preparation for the user campaign. VEGA 2 system has been tested in different configurations depending on the focusing optics and targets used. One configuration (long focal length thick Al target generating a proton beam with a maximum energy of 10 MeV and temperature of 2.5 MeV. In this paper we present preliminary experimental results.

About 50 years ago, Sarachick and Schappert [Phys. Rev. D. 1, 2738-2752 (1970)] showed that relativistic Thomson scattering leads to wavelength shifts that are proportional to the laser intensity. About 28 years later, Chen et al. [Nature 396, 653-655 (1998)] used these shifts to estimate their laser intensity near $10^{18}$ W/cm$^2$. More recently, there have been several theoretical studies aimed at exploiting nonlinear Thomson scattering as a tool for direct measurement of intensities well into the relativistic regime. We present the first quantitative study of this approach for intensities between $10^{18}$ and $10^{19}$ W/cm$^2$. We show that the spectral shifts are in reasonable agreement with estimates of the peak intensity extracted from images of the focal area obtained at reduced power. Finally, we discuss the viability of the approach, its range of usefulness and how it might be extended to gauge intensities well in excess of $10^{19}$ W/cm$^2$.

We present a scintillator-based detector able to measure the proton energy and the spatial distribution with a relatively simple design. It has been designed and built at the Spanish Center for Pulsed Lasers (CLPU) in Salamanca and tested in the proton accelerator at the Centro de Micro-Análisis de Materiales (CMAM) in Madrid. The detector is capable of being set in the high repetition rate (HRR) mode and reproduces the performance of the radiochromic film detector. It represents a new class of online detectors for laser–plasma physics experiments in the newly emerging high power laser laboratories working at HRR.

This article reports the development, construction, and experimental test of an angle-resolved Thomson parabola (TP) spectrometer for laser-accelerated multi-MeV ion beams in order to distinguish between ionic species with different charge-to-mass ratio. High repetition rate (HHR) compatibility is guaranteed by the use of a microchannel plate (MCP) as active particle detector. The angular resolving power, which is achieved due to an array of entrance pinholes, can be simply adjusted by modifying the geometry of the experiment and/or the pinhole array itself. The analysis procedure allows for different ion traces to cross on the detector plane, which greatly enhances the flexibility and capabilities of the detector. A full characterization of the TP magnetic field is implemented into a relativistic code developed for the trajectory calculation of each pinhole beamlet. We describe the first test of the spectrometer at the $1\mathrm{PW}$ VEGA 3 laser facility at CLPU, Salamanca (Spain), where up to $15\mathrm{MeV}$ protons and carbon ions from a $3\mathsf{\mu }\mathrm{m}$ laser-irradiated Al foil are detected.

Ion acceleration from gaseous targets driven by relativistic-intensity lasers was demonstrated as early as the late 1990s, yet most of the experiments conducted to date have involved picosecond-duration, Nd:glass lasers operating at low repetition rate. Here, we present measurements on the interaction of ultraintense $(\approx {10}^{20}\mathrm{W}{\mathrm{cm}}^{-2}, 1 \mathrm{PW})$, ultrashort $(\approx 70\mathrm{fs})$ Ti:Sa laser pulses with near-critical $(\approx {10}^{20}{\mathrm{cm}}^{-3})$ helium gas jets, a debris-free targetry with the potential for future compatibility with high $(\approx 1 \mathrm{Hz})$ repetition rate operation. We provide evidence of $\alpha$ particles being forward accelerated up to $\approx 2.7\text{−}\mathrm{MeV}$ energy with a total flux of $\approx {10}^{11}{\mathrm{sr}}^{-1}$ as integrated over $>0.1\text{−}\mathrm{MeV}$ energies and detected within a $0.5\text{−}\mathrm{mrad}$ solid angle. We also report on on-axis emission of relativistic electrons with an exponentially decaying spectrum characterized by a $\approx 10\text{−}\mathrm{MeV}$ slope, i.e., five times larger than the standard ponderomotive scaling. The total charge of these electrons with energy above 2 MeV is estimated to be of $\approx 1\mathrm{nC}$, corresponding to $\approx 0.1\%$ of the laser drive energy. In addition, we observe the formation of a plasma channel, extending longitudinally across the gas density maximum and expanding radially with time. These results are well captured by large-scale particle-in-cell simulations, which reveal that the detected fast ions most likely originate from reflection off the rapidly expanding channel walls. The latter process is predicted to yield ion energies in the MeV range, which compare well with the measurements. Finally, direct laser acceleration is shown to be the dominant mechanism behind the observed electron energization.