Laser Particle Acceleration Research Articles

Radiobiological Effectiveness of Laser Accelerated Electrons in Comparison to Electron Beams from a Conventional Linear Accelerator

The notable progress in laser particle acceleration technology promises potential medical application in cancer therapy through compact and cost effective laser devices that are suitable for already existing clinics. Previously, consequences on the radiobiological response by laser driven particle beams characterised by an ultra high peak dose rate have to be investigated. Therefore, tumour and non-malignant cells were irradiated with pulsed laser accelerated electrons at the JETI facility for the comparison with continuous electrons of a conventional therapy LINAC. Dose response curves were measured for the biological endpoints clonogenic survival and residual DNA double strand breaks. The overall results show no significant differences in radiobiological response for in vitro cell experiments between laser accelerated pulsed and clinical used electron beams. These first systematic in vitro cell response studies with precise dosimetry to laser driven electron beams represent a first step toward the long term aim of the application of laser accelerated particles in radiotherapy.

Laser–matter interaction at ultra-relativistic intensities

The chirped-pulse amplification technique has opened up a completely new scenario in laser–matter interaction. Radiation intensities in excess of 1018 W/cm2, leading to relativistic electron motion in the laser field, induce phenomena (sometimes very spectacular) concerning laser pulse propagation, particle acceleration and generation of energetic electromagnetic radiation. The suitable utilization of such phenomena allows for several applications, including the fast ignition of an inertially confined fusion target, the production of energetic particles (electrons, protons, ions and positrons), and X-gamma rays for medical diagnostics and therapy.

Status and future prospects of laser fusion and high power laser applications

In Asia, there are many institutes for the R&D of high power laser science and applications. They are 5 major institutes in Japan, 4 major institutes in China, 2 institutes in Korea, and 3 institutes in India. The recent achievements and future prospects of those institutes will be over viewed.In the laser fusion research, the FIREX-I project in Japan has been progressing. The 10kJ short pulse LFEX laser has completed and started the experiments with a single beam. About 1kJ pulse energy will be injected into a cone target. The experimental results of the FIREX experiments will be presented. As the target design for the experiments, a new target, namely, a double cone target was proposed, in which the high energy electrons are well confined and the heating efficiency is significantly improved. Together with the fusion experiments, Osaka University has carried out laboratory astrophysics experiments on photo ionizing plasmas to observe a unique X-ray spectrum from non-LTE plasmas. In 2008, Osaka university has started a new Photon research center in relation with the new program: Consortium for Photon Science and Technology: C-PhoST, in which ultra intense laser plasmas research and related education will be carried out for 10 years.At APRI, JAEA, the fundamental science on the relativistic laser plasmas and the applications of laser particle acceleration has been developed. The application of laser ion acceleration has been investigated on the beam cancer therapy since 2007.In China, The high power glass laser: Shenguan-II and a peta watt beam have been operated to work on radiation hydro dynamics at SIOFM Shanghai. The laser material and optics are developed at SIOFM and LFRC. The IAPCM and the IOP continued the studies on radiation hydrodynamics and on relativistic laser plasmas interactions. At LFRC in China, the construction of Shenguan III glass laser of 200kJ in blue has progressed and will be completed in 2012.Together with the Korean program, I will overview the above Asian programs.

SU-GG-T-459: Laser-Based Particle Acceleration for Future Ion Therapy: Current Status of the Joint Project OnCOOPtics with Special Focus on Beam Delivery and Dosimetry

Purpose: Before the novel technology of laser-based particle acceleration can be used for clinical applications, several requirements have to be fulfilled. These are the supply of stable and reliable particle beams with reproducible properties, sufficient particle intensity and useable energy spectra. Additionally, a precise dose delivery in an appropriate time and the exposure of a desired irradiation field are needed. Beside these demands, consequences on dosimetry as well as on the radiobiological effect have to be investigated for ultra-short pulsed laser-accelerated particle beams. Method and Materials: The joint project onCOOPtics, an interdisciplinary and multicenter institution focusing on the development of a laser particle accelerator for radiation oncology, is introduced. The worldwide first systematic in vitro irradiations with laser-accelerated electrons performed with the JeTi laser system will be presented focusing on the experimental setup, practical experiences and on dosimetric and radiobiological results. In a next step, cell irradiation experiments with laser-accelerated protons have been prepared. Therefore, a dedicated dosimetric system was developed. It is integrated into a device that can be installed at different laser and conventional accelerators and serves also as cell or animal irradiation device. Results: A laser accelerator was successfully optimized for systematic radiobiological experiments performed over 3 months. No significant differences between laser-accelerated and conventional 6 MeV electron beams were found. An integrated dosimetry and cell irradiation device for systematic in vitro and in vivo experiments with laser-accelerated protons was developed, characterized, calibrated and successfully tested with both continuous and pulsed proton beams. Cell irradiations with protons have been started. Conclusion: Laser accelerators can be used for radiobiological experiments, meeting all necessary requirements like homogeneity, stability and precise dose delivery. Nevertheless, before fulfilling the much higher requirements for clinical application, several improvements concerning i.e. proton energy, spectral shaping and patient safety are necessary. Supported by BMBF (03ZIK445).

Excitation of an upper hybrid wave by two intense laser beams and particle acceleration

This Letter presents an investigation of the excitation of an upper hybrid wave (UHW) by cross focusing of two intense laser beams in a collisionless hot magnetoplasma, when relativistic and ponderomotive nonlinearities are operative. The electric vectors of the two beams are polarized along uniform static magnetic field and the beams propagate perpendicular to the static magnetic field. Analytical expressions for the beam width of the laser beams, electric vector and power of the excited UHW and energy gain have been obtained. The UHW generation at the difference frequency and particle acceleration has also been studied. The nonlinear coupling between intense laser beams and UHW is so strong that UHW gets excited and a large fraction of the laser beam energy gets transferred to UHW and this UHW accelerates electrons. It has been shown that the presence of a magnetic field affects significantly the power of the UHW and energy gain by the electron in the presence of the UHW.

Spectral shaping of laser generated proton beams

The rapid progress in the field of laser particle acceleration has stimulated a debate about the promising perspectives of laser based ion beam sources. For a long time, the beams produced exhibited quasi-thermal spectra. Recent proof-of-principle experiments demonstrated that ion beams with narrow energy distribution can be generated from special target geometries. However, the achieved spectra were strongly limited in terms of monochromacity and reproducibility. We show that microstructured targets can be used to reliably produce protons with monoenergetic spectra above 2 MeV with less than 10% energy spread. Detailed investigations of the effects of laser ablation on the target resulted in a significant improvement of the reproducibility. Based on statistical analysis, we derive a scaling law between proton peak position and laser energy, underlining the suitability of this method for future applications. Both the quality of the spectra and the scaling law are well reproduced by numerical simulations.

High index of refraction via quantum interference in a three-level system of Er 3+ -doped yttrium aluminium garnet crystal

A simple three-level system is proposed to produce high index of refraction with zero absorption in an Er3+-doped yttrium aluminium garnet (YAG) crystal, which is achieved for a probe field between the excited state 4I13/2 and ground state 4I15/2 by adjusting a strong coherent driving field between the upper excited state 4I11/2 and 4I15/2. It is found that the changes of the frequency of the coherent driving field and the concentration of Er3+ ions in the YAG crystal can maximize the index of refraction accompanied by vanishing absorption. This result could be useful for the dispersion compensation in fibre communication, laser particle acceleration, high precision magnetometry and so on.

Quasimonoenergetic Deuteron Bursts Produced by Ultraintense Laser Pulses

We report on the generation and laser acceleration of bunches of energetic deuterons with a small energy spread at about 2 MeV. This quasimonoenergetic peak within the ion energy spectrum was observed when heavy-water microdroplets were irradiated with ultrashort laser pulses of about 40 fs duration and high (10(-8)) temporal contrast, at an intensity of 10(19) W/cm(2). The results can be explained by a simple physical model related to spatial separation of two ion species within a finite-volume target. The production of quasimonoenergetic ions is a long-standing goal in laser-particle acceleration; it could have diverse applications such as in medicine or in the development of future compact ion accelerators.

Preliminary evidences of AC-run-away in femtosecond laser-matter interaction

The role of collisional absorption is shown to be important at the beginning of the interaction between a laser pulse and matter, i.e., a plasma, while later on collective absorption phenomena take place. The scope of this paper is to present first results about the long predicted AC-run-away effect, defined as a sudden transition from a collisional absorption regime to a collective one, in ideal circumstances: for an ultrashort laser pulse, i.e., subpicosecond pulses, and with a sharp plasma boundary, i.e., without a laser prepulse. For this purpose, we use a kinetic model based on the ballistic theory. The model is of relevance to laser-matter interaction including laser nuclear fusion or laser particle acceleration.

Novel techniques of laser acceleration: from structures to plasmas

Compact accelerators of the future will require enormous accelerating gradients that can only be generated using high power laser beams. Two novel techniques of laser particle acceleration are discussed. The first scheme is based on a solid-state accelerating structure powered by a short pulse CO(2) laser. The planar structure consists of two SiC films, separated by a vacuum gap, grown on Si wafers. Particle acceleration takes place inside the gap by a surface electromagnetic wave excited at the vacuum/SiC interface. Laser coupling is accomplished through the properly designed Si grating. This structure can be inexpensively manufactured using standard microfabrication techniques and can support accelerating fields well in excess of 1 GeV m(-1) without breakdown. The second scheme utilizes a laser beatwave to excite a high-amplitude plasma wave, which accelerates relativistic particles. The novel aspect of this technique is that it takes advantage of the nonlinear bi-stability of the relativistic plasma wave to drive it close to the wavebreaking.

Effect of relativistic mutual interaction of two laser beams on the growth of laser ripple in plasma

This paper presents an effect of relativistic mutual interaction of two laser beams of different frequencies on the growth of a laser ripple in laser produced plasmas. The nonlinearity due to relativistic mass variation depends not only on the intensity of one laser but also on the second laser. Therefore, one laser beam affects the dynamics of the second beam and hence a mutual nonlinear interaction (cross-focusing) takes place. The dynamical equations governing the laser intensity of two laser beams and the perturbation present on one laser beam (ripple) have been set up and a numerical solution has been presented for typical laser plasma parameters. It is found that a change in the intensity of the second laser beam can affect the growth of the laser ripple significantly. This study is important in plasma beat wave excitation and collective laser particle accelerators.

Present status and future prospects of IFE and high power laser research in Asia

The present status and future prospects of IFE research and high power laser applications in Asia are reviewed. At ILE, Osaka University, the Gekko XII and the Peta Watt laser system have been operated to investigate implosion hydrodynamics, fast ignition and relativistic laser plasma interactions. In particular, fast ignition experiments with cone shell targets have been carried out as joint UK–Japan and US–Japan collaboration programmes. In the experiments, imploded high density plasmas are heated by a 500 J level petawatt laser pulse. The thermal neutron yield is found to increase by three orders of magnitude by petawatt laser injection to the cone shell target.Laser plasma physics related to laser fusion and other applications has been studied at many institutes in Asia. Areas of research include Rayleigh–Taylor instability experiments, application of extreme ultraviolet radiation sources for lithography, laser particle acceleration, and x-ray lasers, to name a few.

Application of novel techniques for interferogram analysis to laser–plasma femtosecond probing

Recently, two novel techniques for the extraction of the phase-shift map (Tomassini et al. (2001). Applied Optics40, 35) and the electronic density map estimation (Tomassini P. & Giulietti A. (2001). Optics Communication199, 143–148) have been proposed. In this article, we apply both methods to a sample laser–plasma interferogram obtained with femtoseconds probe pulse, in an experimental setup devoted to laser particle acceleration studies.

Relativistic cross-focusing of two coaxial Gaussian laser beams in a plasma

The paper presents a paraxial theory of the relativistic cross-focusing of two coaxial Gaussian laser beams of different frequencies in a homogeneous plasma. We discuss the self-focusing of a weaker laser beam in the plasma due to the optical inhomogeneities introduced by another stronger copropagating laser beam. In the presence of the second stronger beam (Pcr21<P2<Pcr22), the plasma behaves as an oscillatory waveguide for the first, weaker, beam (P1<Pcr11) as it propagates in the plasma. When both the beams are strong (Pcr11,21<P1,2<Pcr12,22), the nonlinearities introduced by the relativistic effect are additive in nature, such that one beam can undergo oscillatory self-focusing and the other simultaneously defocusing, and vice versa. A comparison reveals that cross-focusing due to relativistic nonlinearity is possible for a wider range of powers of the laser pulses than is cross-focusing due to ponderomotive nonlinearity. Relativistic cross-focusing is important in plasma beat-wave excitation and collective laser particle accelerators.

Nonlinear interaction of ultra-intense laser pulses with a thin foil

The nonlinear interaction of an ultraintense laser pulse with a thin foil modifies the shape, the frequency content and the polarization of the pulse. An analytical description of this interaction is presented, together with the results of 1D3V and 2D3V particle in cell simulations. The conditions for the relativistic transparency of a thin foil are given and are shown to lead to the sharpening of the laser pulse. Such a pulse shape is advantageous for Laser Plasma Wakefield Acceleration of charged particles. In addition it is shown that a thin foil makes it possible to extract the accelerated particles nonadiabatically in the case of laser particle acceleration in vacuum.

Multiple dynamic scettering of laser radiation on a light-induced jet of microparticles in suspension

A self-consistent theoretical analysis is made of the multiple scattering of coherent laser radiation in a random medium under conditions of formation of a light-induced jet of scatterers. It is shown, that the laser particle acceleration leads to a qualitative change of the temporal auto-correlation function of scattered light as compared to the case of scattering on chaotically moving Brownian particles. The effect of radiation absorption on the temporal coherence of the multiple-scattered light under conditions of light-induced particle motion in the scattering medium is studied.

Laser particle acceleration: beat-wave and wakefield experiments

In a plasma, some of the energy of a high-power laser beam can be transferred to a longitudinal plasma wave with a high phase velocity. This wave can in turn accelerate relativistic charged particles to very high energies. Several mechanisms have been proposed to generate these intense electric fields and some of them have already been tested experimentally. Using the beat wave method, electric fields of 1 - 10 have been produced and electrons have been accelerated with an energy gain from 1 MeV to more than 30 MeV. Some preliminary experiments have shown that electrons can be accelerated in plasma waves generated by the wakefield method. In the case of self-modulated wakefield, electric fields larger than 100 trap electrons and eject them from the plasma with an energy up to 100 MeV. The perspectives in the near future are the production of intense and short electron beams of a few MeV and the acceleration of electrons up to 1 GeV. To reach an energy of 1 TeV and get closer to the parameters required by the high-energy physicists, one will have to test some new methods to be able to guide the laser beam over large distances.

Laser acceleration of particles

Laser acceleration of particles

Multistaging in free-space laser particle accelerators

One important issue with regard to acceleration of electrons in free space using intense laser beams is the phase slippage of the electrons relative to the electromagnetic field. This arises from a phase velocity mismatch between the electron and light wave. Left uncontrolled this slippage can result in degradation of the e-beam characteristics (e.g., emittance) and dispersion of the electron bunches. By a method similar to microwave accelerators, multistaging offers a means to control the e-beam evolution by tuning each successive stage. The phase of the electron bunches relative to the laser field at the entrance of each section determines the acceleration and/or focusing that ensues in that section; therefore, the entrance phase is a natural tuning parameter. It is shown that by controlling the entrance phase it is possible to preserve the e-beam quality, both transverse (emittance) and longitudinal (bunching, energy spread). Calculations of the longitudinal and transverse beam dynamics are performed to determine the evolution of a finite-emittance e beam from stage to stage. By this method the conditions on entrance phase that allow successful e-beam trapping are found. It is also shown that conditions that assure e-beam trapping automatically preserve the overall beam quality.

Efficient radially polarized laser beam generation with a double interferometer

Conversion of a linearly polarized CO(2) laser beam into a radially polarized beam is demonstrated with a novel double-interferometer system. The first Mach-Zehnder interferometer converts the linearly polarized input beam into two beams with sin(2) θ and cos(2) θ intensity profiles, where θ is the azimuthal angle. This is accomplished by using two spiral-phase-delay plates with opposite handedness in the two legs of the interferometer to impart a one-wave phase delay azimuthally across the face of the beams. After these beams are interfered with, the resulting beams are sent directly into the second Mach-Zehnder interferometer, where the polarization direction of one beam is rotated by 90°. The beams are then recombined at the output of the second interferometer with a polarization-sensitive beam splitter to generate a radially polarized beam. The output beam is ≈92% radially polarized and contains ≈85% of the input power. This system will be used in upcoming laser particle acceleration experiments.