Optical diagnostics for density measurement in high-quality laser-plasma electron accelerators

Implementation of laser-plasma-based acceleration stages in user-oriented facilities requires the definition and deployment of appropriate diagnostic methodologies to monitor and control the acceleration process. An overview is given here of optical diagnostics for density measurement in laser-plasma acceleration stages, with emphasis on well-established and easily implemented approaches. Diagnostics for both neutral gas and free-electron number density are considered, highlighting real-time measurement capabilities. Optical interferometry, in its various configurations, from standard two-arm to more advanced common-path designs, is discussed, along with spectroscopic techniques such as Stark broadening and Raman scattering. A critical analysis of the diagnostics presented is given concerning their implementation in laser-plasma acceleration stages for the production of high-quality GeV electron bunches

Intra-cycle depolarization of ultraintense laser pulses focused by off-axis parabolic mirrors

A study of the structure of the electric and magnetic fields of ultraintense laser pulses focused by an off-axis parabolic mirror is reported. At first, a theoretical model is laid out, whose final equations integration allows the space and time structure of the fields to be retrieved. The model is then employed to investigate the field patterns at different times within the optical cycle, for off-axis parabola parameters normally employed in the context of ultraintense laser–plasma interaction experiments. The results show that nontrivial, complex electromagnetic field patterns are observed at the time at which the electric and magnetic fields are supposed to vanish. The importance of this effect is then studied for different laser polarizations, $f$ numbers and off-axis angles

Overview and specifications of laser and target areas at the Intense Laser Irradiation Laboratory

Abstract We present the main features of the ultrashort, high-intensity laser installation at the Intense Laser Irradiation Laboratory (ILIL) including laser, beam transport and target area specifications. The laboratory was designed to host laser–target interaction experiments of more than 220 TW peak power, in flexible focusing configurations, with ultrarelativistic intensity on the target. Specifications have been established via dedicated optical diagnostic assemblies and commissioning interaction experiments. In this paper we give a summary of laser specifications available to users, including spatial, spectral and temporal contrast features. The layout of the experimental target areas is presented, with attention to the available configurations of laser focusing geometries and diagnostics. Finally, we discuss radiation protection measures and mechanical stability of the laser focal spot on the target

Summary of WG7—High brightness Power Sources: From Laser Technology to Beam Drivers

In this paper we summarize the contributions presented during the Working Group 7 (WG7) sessions, dedicated to high brightness power sources. In this context we have tackled several topics of high relevance to novel accelerators, including laser technology for laser driven accelerators, the state of the art of high peak and average power lasers, the laser beam quality, contrast and stability. A number of novel results were presented especially in the area of laser beam characterization and control, advanced laser concepts, target control and electron beam diagnostics currently under development at a range of labs engaged in the development of advanced accelerator concepts

Conceptual Design of a Laser Driver for a Plasma Accelerator User Facility

The purpose of the European project EuPRAXIA is to realize a novel plasma accelerator user facility. The laser driven approach sets requirements for a very high performance level for the laser system: pulse peak power in the petawatt range, pulse repetition rate of several tens of Hz, very high beam quality and overall stability of the system parameters, along with 24/7 operation availability for experiments. Only a few years ago these performances were considered unrealistic, but recent advances in laser technologies, in particular in the chirped pulse amplification (CPA) of ultrashort pulses and in high energy, high repetition rate pump lasers have changed this scenario. This paper discusses the conceptual design and the overall architecture of a laser system operating as the driver of a plasma acceleration facility for different applications. The laser consists of a multi-stage amplification chain based CPA Ti:Sapphire, using frequency doubled, diode laser pumped Nd or Yb solid state lasers as pump sources. Specific aspects related to the cooling strategy of the main amplifiers, the operation of pulse compressors at high average power, and the beam pointing diagnostics are addressed in detail

High quality electron bunches for a multistage GeV accelerator with resonant multipulse ionization injection

International audienceLaser wakefield acceleration of GeV electrons is becoming a mature technique, so that a reliable accelerator delivering stable beams to users communities can now be considered. In such a context, two plasma stages, one injector and one booster stage, offer a flexible solution for optimization. For the injector we consider here the resonant multipulse ionization injection (ReMPI) that can be optimized to generate electron bunches with high enough quality to be efficiently transported to the second stage. In order to better control the beam-loading effect and optimize the beam manipulation after the plasma downramp, a quasiround beam is preferable. In this respect, we present analytical and particle-in-cell results concerning the tunnel-ionization process in presence of two, orthogonally polarized, laser pulses with different wavelengths. We also show, by means of hybrid fluid/PIC numerical simulations, that a stable working point with the ReMPI injector exists at 32 pC, 4 kA peak current, with mean energy of 150 MeV, energy spread of 1.65% rms, normalized emittance εn=0.23  μm and divergence of 0.6 mrad. The scheme relies on a 150 TW Ti:Sa laser modified to achieve a four-pulses driver train and a third harmonics ionization pulse

Focusing and stabilizing laser?plasma-generated electron beams with magnetic devices

External magnetic devices have been successfully tested to control the divergence and pointing stability of subrelativistic electron beams accelerated by ultrashort laser pulses in a nitrogen plasma (electron density of >1019cm%3). Different configurations of the magnetic devices have been studied, and their effects are discussed in detail. The analysis is also supported by the results of ray-tracing simulations using the first-order trajectory equation in the magnetic field configurations. This simple method of improving beam stability will be particularly useful for applying laser generated ultrashort electron beams to high-dose radiobiological studies. © 2014 The Japan Society of Applied Physic