Laser Particle Acceleration Research Articles

Visualizing plasmons and ultrafast kinetic instabilities in laser-driven solids using X-ray scattering

Ultra-intense lasers that ionize atoms and accelerate electrons in solids to near the speed of light can lead to kinetic instabilities that alter the laser absorption and subsequent electron transport, isochoric heating, and ion acceleration. These instabilities can be difficult to characterize, but X-ray scattering at keV photon energies allows for their visualization with femtosecond temporal resolution on the few nanometer mesoscale. Here, we perform such experiment on laser-driven flat silicon membranes that shows the development of structure with a dominant scale of 60 nm in the plane of the laser axis and laser polarization, and 95 nm in the vertical direction with a growth rate faster than 0.1 fs−1. Combining the XFEL experiments with simulations provides a complete picture of the structural evolution of ultra-fast laser-induced plasma density development, indicating the excitation of plasmons and a filamentation instability. Particle-in-cell simulations confirm that these signals are due to an oblique two-stream filamentation instability. These findings provide new insight into ultra-fast instability and heating processes in solids under extreme conditions at the nanometer level with possible implications for laser particle acceleration, inertial confinement fusion, and laboratory astrophysics.

Optimizing laser coupling, matter heating, and particle acceleration from solids using multiplexed ultraintense lasers

Optimizing laser coupling, matter heating, and particle acceleration from solids using multiplexed ultraintense lasers

Optimization of sub-relativistic co-propagating accelerating structures.

In this paper, novel optimization methodologies of sub-relativistic guided interaction structures for dielectric laser particle acceleration (DLA) are presented. In particular, we focus on co-propagating geometries based on slot waveguides in continuous wave (CW) operation, where the particle flow and the direction of propagation of the accelerating field are co-linear. Since the velocity of sub-relativistic particles varies along the acceleration path, proper tapering of the waveguide geometry is required to achieve an extended acceleration region, and, thus a large energy gain. The design of an optimal taper ensuring particle-wave synchronicity and maximum energy gain is pursued through a physics-based approach, and these results are compared, for validation, with the outcomes of a downhill simplex method searching algorithm. Additionally, the application of a simplified 2D model of the accelerating slot waveguide is investigated and profitably used to get qualitative results useful for fast structure optimization. Indeed, this approach can hold significant potential for the development of novel accelerating structures, as it enables a thorough and fast exploration of the design space.

Generation of terahertz vector beam bearing tailored topological charge

Optical vector beams have great potential in many applications, for example optical tweezers, information transmission and processing, laser surface structuring, particle acceleration, and vortex dichroism spectroscopy. However, the reported vector beams in the terahertz (THz) spectral range are limited to exhibiting only low-order topological charges. Therefore, methodologies to generate THz vector beams bearing a tailored topological charge are highly desired. This work investigates how to generate THz vector beams with a tailored topological charge via the optical rectification process in a 111-cut ZnTe crystal pumped with a vector optical beam and how to manipulate the vector THz beam’s polarization state through the initial polarization angle. We theoretically and experimentally demonstrate that the transduction process produces a THz topological charge twice that of the infrared pump, also admitting the opposite sign. Given the well-developed technology to design infrared vector beams, the proposed method can generate THz vector beams with tailored topological charges.

Tango Controls and data pipeline for petawatt laser experiments

Abstract The Centre for Advanced Laser Applications in Garching, Germany, is home to the ATLAS-3000 multi-petawatt laser, dedicated to research on laser particle acceleration and its applications. A control system based on Tango Controls is implemented for both the laser and four experimental areas. The device server approach features high modularity, which, in addition to the hardware control, enables a quick extension of the system and allows for automated data acquisition of the laser parameters and experimental data for each laser shot. In this paper we present an overview of our implementation of the control system, as well as our advances in terms of experimental operation, online supervision and data processing. We also give an outlook on advanced experimental supervision and online data evaluation – where the data can be processed in a pipeline – which is being developed on the basis of this infrastructure.

Generation of long range low-divergent Gauss–Bessel beams by annihilating optical vortices

Bessel beams are remarkable since they do not diverge. Accordingly, they have numerous applications ranging from precision laser micro-machining to laser particle acceleration. We demonstrate a novel approach for generating long-range Gauss–Bessel beams. A ring-shaped beam is produced by imprinting a vortex with high topological charge in a Gaussian beam. The phase singularities are thereafter removed and the ring-shaped beam focused/Fourier-transformed by a thin lens. This results in a remarkably good realization of a Gauss–Bessel beam. Divergence angles in the microradian range and Gauss–Bessel beam lengths up to 2.5 m behind the focal plane of the lens are demonstrated.

Topological investigation of laser ion acceleration

Laser particle acceleration is examined from a topological viewpoint which analyses laser pulse irradiation on a thin foil target using two-dimensional particle-in-cell simulations. Laser ion acceleration schemes are classified by topology depending on whether the target after laser irradiation (deformed target) is homeomorphic to the initial target. When the deformed target is non-homeomorphic, high energy ions are generated with high efficiency, which is considerably influenced by the target thickness. However, when the deformed and initial targets are homeomorphic, the obtained ion energy is low and is less influenced by the target thickness.

Production of HD Molecules in Definite Hyperfine Substates.

Polarized atomic beam sources have been in operation for many years to produce either nuclear polarized atomic hydrogen or deuterium beams. In recent experiments, such a source was used to polarize both isotopes independently at the same time. By recombination of the atoms, hydrogen-deuterium molecules with all possible nuclear spin combinations can be created. Those spin isomers are useful for further applications, like precision spectroscopy, as polarized targets for laser-particle acceleration, polarized fuel for fusion reactors, or as an option for future measurements of electric dipole moments.

A survey of fiber laser technology in light of laser particle accelerator

Fiber laser technology and related performance and maturity are surveyed with the perspectives of laser acceleration. Advantageous fiber attributes allow high efficiencies in energy-conversion and heat removal and superior performance in high repetition. Wide utilization in the industries has led to high reliability and cost effectiveness in fiber laser technology. With coherent combination of fiber amplifiers, average-power and peak-power levels are targeted for practical laser-driven plasma acceleration applications.

High-order harmonic generation from a solid-surface plasma by relativistic-intensity sub-100-fs mid-infrared pulses.

High-order harmonic generation (HHG) in plasmas induced by ultrashort, relativistic-intensity laser pulses on solid surfaces can provide an efficient source of attosecond pulses and opens routes toward new regimes of laser-matter interactions, x-ray generation, laser particle acceleration, and relativistic nonlinear optics. However, field intensities in the range of Irel∼1019 W/cm2 are typically needed to achieve the relativistic regime of HHG in experiments with near-infrared laser pulses. Here, we show that, in the mid-infrared range, due to the λ-2 scaling of Irel with the driver wavelength λ, relativistic HHG can be observed at much lower levels of laser field intensities. High-peak-power 80-fs, 3.9-μm pulses are focused in our experiments on a solid surface to provide field intensities in the range of 1017 W/cm2. Remarkably, this level of field intensities, considered as low by the standards of relativistic optics in the near infrared, is shown to be sufficient for generation of high-order harmonics with signature properties of relativistic HHG-beam directionality, spectra with extended plateaus, and a high HHG yield sustained for both p- and s-polarized driver fields.

Combining two-photon-polymerization with UV-lithography for laser particle acceleration targets

In the field of laser driven particle acceleration, many experiments with plain foil targets have been performed to investigate ion acceleration mechanisms such as TNSA and BOA. A more complex target geometry, for which the front and rear surface can be structured in a deterministic way, will lead to a better understanding of e.g. the actual source size, laser contrast related effect to the coupling efficiency of laser energy into the target of specifically shaped target surfaces or means to reduce the particle beam divergence such as ballistic focusing. A promising technology to manufacture complex 3D freeform targets is the two-photon-polymerization. With resolutions better than 200 nm, it is possible to create small targets with microstructured surfaces. We implemented the combination of two-photon-polymerization and UV-lithography to facilitate the handling of such small structures.

Propagation of two intense cosh-Gaussian laser beams in plasma in the relativistic-ponderomotive regime

This work presents an investigation of the propagation of two intense cosh-Gaussian laser beams (CGLBs) in collisionless plasma taking into account the combined effects of relativistic and ponderomotive nonlinearities. Due to mutual interaction of two CGLBs, the self-focusing of one beam is affected by the presence of another beam in plasma, and cross-focusing takes place. A paraxial-like approach has been used to investigate the cross-focusing of CGLBs in plasma. An appropriate expression for the nonlinear dielectric constant of plasma has been evaluated in the presence of relativistic-ponderomotive force and used to study the propagation of CGLBs in plasma. The effect of various well-established laser and plasma parameters on the cross-focusing of two beams in plasma has been explored and the results are compared with only relativistic nonlinearity and the Gaussian profile of laser beams. Numerical results show that the decentered parameter (b) plays a crucial role in the cross-focusing of the CGLBs. It is observed that CGLBs focused earlier than Gaussian beams. This study is useful in beat wave excitation of electron plasma wave and collective laser particle accelerators.

Efficient energy absorption of intense ps-laser pulse into nanowire target

The interaction between ultra-intense laser light and vertically aligned carbon nanotubes is investigated to demonstrate efficient laser-energy absorption in the ps laser-pulse regime. Results indicate a clear enhancement of the energy conversion from laser to energetic electrons and a simultaneously small plasma expansion on the surface of the target. A two-dimensional plasma particle calculation exhibits a high absorption through laser propagation deep into the nanotube array, even for a dense array whose structure is much smaller than the laser wavelength. The propagation leads to the radial expansion of plasma perpendicular to the nanotubes rather than to the front side. These features may contribute to fast ignition in inertial confinement fusion and laser particle acceleration, both of which require high current and small surface plasma simultaneously.

Controllable laser ion beam generation

In intense-laser plasma interaction, several issues still remain to be solved for a future laser particle acceleration. In this paper we focus on a bunching of ion beam, which is preaccelerated by a strong electric field generated in a laser plasma interaction. In this study, a nearcritical-density plasma target is illuminated by an intense short laser pulse. A moving strong inductive electric field is generated inside of the target. We have successfully obtained a bunched ion beam in our particle-in-cell simulations in this paper.

Stack and dump: Peak-power scaling by coherent pulse addition in passive cavities

During the last decades femtosecond lasers have proven their vast benefit in both scientific and technological tasks. Nevertheless, one laser feature bearing the tremendous potential for high-field applications, delivering extremely high peak and average powers simultaneously, is still not accessible. This is the performance regime several upcoming applications such as laser particle acceleration require, and therefore, challenge laser technology to the fullest. On the one hand, some state-of-the-art canonical bulk amplifier systems provide pulse peak powers in the range of multi-terawatt to petawatt. On the other hand, concepts for advanced solid-state-lasers, specifically thin disk, slab or fiber systems have shown their capability of emitting high average powers in the kilowatt range with a high wall-plug-efficiency while maintaining an excellent spatial and temporal quality of the output beam. In this article, a brief introduction to a concept for a compact laser system capable of simultaneously providing high peak and average powers all along with a high wall-plug efficiency will be given. The concept relies on the stacking of a pulse train emitted from a high-repetitive femtosecond laser system in a passive enhancement cavity, also referred to as temporal coherent combining. In this manner, the repetition rate is decreased in favor of a pulse energy enhancement by the same factor while the average power is almost preserved. The key challenge of this concept is a fast, purely reflective switching element that allows for the dumping of the enhanced pulse out of the cavity. Addressing this challenge could, for the first time, allow for the highly efficient extraction of joule-class pulses at megawatt average power levels and thus lead to a whole new area of applications for ultra-fast laser systems.

A concept for multiterawatt fibre lasers based on coherent pulse stacking in passive cavities

Since the advent of femtosecond lasers, performance improvements have constantly impacted on existing applications and enabled novel applications. However, one performance feature bearing the potential of a quantum leap for high-field applications is still not available: the simultaneous emission of extremely high peak and average powers. Emerging applications such as laser particle acceleration require exactly this performance regime and, therefore, challenge laser technology at large. On the one hand, canonical bulk systems can provide pulse peak powers in the multi-terawatt to petawatt range, while on the other hand, advanced solid-state-laser concepts such as the thin disk, slab or fibre are well known for their high efficiency and their ability to emit high average powers in the kilowatt range with excellent beam quality. In this contribution, a compact laser system capable of simultaneously providing high peak and average powers with high wall-plug efficiency is proposed and analysed. The concept is based on the temporal coherent combination (pulse stacking) of a pulse train emitted from a high-repetition-rate femtosecond laser system in a passive enhancement cavity. Thus, the pulse energy is increased at the cost of the repetition rate while almost preserving the average power. The concept relies on a fast switching element for dumping the enhanced pulse out of the cavity. The switch constitutes the key challenge of our proposal. Addressing this challenge could, for the first time, allow the highly efficient dumping of joule-class pulses at megawatt average power levels and lead to unprecedented laser parameters. Coherent pulse stacking may allow compact fibre-laser systems to be used in laser-based particle accelerators, report scientists in Germany. Such accelerators require lasers that can simultaneously provide exceedingly high peak and average powers—a tall order indeed. Now, Sven Breitkopf and co-workers propose that it could be achieved by employing temporal coherent combination of a pulse train emitted by a high-repetition-rate femtosecond fibre laser in a passive cavity. Following pulse stacking, a fast switching element dumps the enhanced high-peak power pulse from the cavity. Although this process increases the pulse peak power at the expense of a lower repetition rate, it retains a high average power. Ultimately, the scheme could lead to Joule-class pulses with terawatt peak powers and megawatt average powers.

SU-D-BRE-05: Feasibility and Limitations of Laser-Driven Proton Therapy: A Treatment Planning Study

Purpose: Laser-acceleration of particles may offer a cost- and spaceefficient alternative for future radiation therapy with particles. Laser-driven particle beams are pulsed with very short bunch times, and a high number of particles is delivered within one laser shot which cannot be portioned or modulated during irradiation. The goal of this study was to examine whether good treatment plans can be produced for laser-driven proton beams and to investigate the feasibility of a laser-driven treatment unit. Methods: An exponentially decaying proton spectrum was tracked through a gantry and energy selection beam line design to produce multiple proton spectra with different energy widths centered on various nominal energies. These spectra were fed into a treatment planning system to calculate spot scanning proton plans using different lateral widths of the beam and different numbers of protons contained in the initial spectrum. The clinical feasibility of the resulting plans was analyzed in terms of dosimetric quality and the required number of laser shots as an estimation of the overall treatment time. Results: We were able to produce treatment plans with plan qualities of clinical relevance for a maximum initial proton number per laser shot of 6*108. However, the associated minimum number of laser shots was in the order of 104, indicating a long delivery time in the order of at least 15 minutes, when assuming an optimistic repetition rate of the laser system of 10 Hz. Conclusion: With the simulated beam line and the assumed shape of the proton spectrum it was impossible to produce clinically acceptable treatment plans that can be delivered in a reasonable time. The situation can be improved by a method or a device in the beam line which can modulate the number of protons from shot to shot. Supported by DFG Cluster of Excellence: Munich-Centre for Advanced Photonics.

NAIS: Nuclear activation-based imaging spectroscopy

In recent years, the development of high power laser systems led to focussed intensities of more than 10(22) W/cm(2) at high pulse energies. Furthermore, both, the advanced high power lasers and the development of sophisticated laser particle acceleration mechanisms facilitate the generation of high energetic particle beams at high fluxes. The challenge of imaging detector systems is to acquire the properties of the high flux beam spatially and spectrally resolved. The limitations of most detector systems are saturation effects. These conventional detectors are based on scintillators, semiconductors, or radiation sensitive films. We present a nuclear activation-based imaging spectroscopy method, which is called NAIS, for the characterization of laser accelerated proton beams. The offline detector system is a combination of stacked metal foils and imaging plates (IP). After the irradiation of the stacked foils they become activated by nuclear reactions, emitting gamma decay radiation. In the next step, an autoradiography of the activated foils using IPs and an analysis routine lead to a spectrally and spatially resolved beam profile. In addition, we present an absolute calibration method for IPs.

Progress in laser acceleration of particles

Laser acceleration of particles is currently a very active area of research in Plasma Physics, with an emphasis on acceleration of electrons and ions using short but intense laser pulses. In this special issue we access the current status of this field by inviting leading researchers all over the world to contribute their original works here. Many of these results were first presented at the recent Laser-Particle Acceleration Workshop (LPAW 2011) held in Wuzhen, China in June 2011. In addition to the laser wakefield acceleration (LWFA) of electrons (Tzoufras et al.) and laser acceleration of ions (Tsung et al.), there were exciting new proposals for a proton-driven plasma wakefield accelerator (Xia et al.) and for a dielectric-structure-based two-beam accelerator (Gai et al.) presented at this workshop, and we are very pleased to have the authors' contributions on these included here.

Estimation of the isentropic parameter in the compression process of the D/3He plasma based on laser particle acceleration energy

In this research, having applied the modeling of D/3He fuel burning, the isentropic parameter and entropy are studied. It is shown that the Fermi degeneracy plays an important role in reducing the pressure, energy driver and the fractional burn-up. Based on recent progresses in the laser particle accelerators’ research, we have examined the ignition of a D/3He fuel to achieve the gains of order 58. The obtained results show that the energy required to compress a D/3He fuel with a density of 3.9 × 104 g/cm3, is 3.3 × 107 J/g. With the confinement parameter, 80 g/cm2 and a two times reduction of the isentropic parameter, the increased rate of the target gain is 31%.