Laser-driven very high energy electron/photon beam radiation therapy in conjunction with a robotic system

We present a new external-beam radiation therapy system using very-high-energy (VHE) electron/photon beams generated by a centimeter-scale laser plasma accelerator built in a robotic system. Most types of external-beam radiation therapy are delivered using a machine called a medical linear accelerator driven by radio frequency (RF) power amplifiers, producing electron beams with an energy range of 6-20 MeV, in conjunction with modern radiation therapy technologies for effective shaping of three-dimensional dose distributions and spatially accurate dose delivery with imaging verification. However, the limited penetration depth and low quality of the transverse penumbra at such electron beams delivered from the present RF linear accelerators prevent the implementation of advanced modalities in current cancer treatments. These drawbacks can be overcome if the electron energy is increased to above 50 MeV. To overcome the disadvantages of the present RF-based medical accelerators, harnessing recent advancement of laser-driven plasma accelerators capable of producing 1-GeV electron beams in a 1-cm gas cell, we propose a new embodiment of the external-beam radiation therapy robotic system delivering very high-energy electron/photon beams with an energy of 50-250 MeV; it is more compact, less expensive, and has a simpler operation and higher performance in comparison with the current radiation therapy system

Extreme case of Faraday effect: magnetic splitting of ultrashort laser pulses in plasmas

The Faraday effect, caused by a magnetic-field-induced change in the optical properties, takes place in a vast variety of systems from a single atomic layer of graphenes to huge galaxies. Currently, it plays a pivot role in many applications such as the manipulation of light and the probing of magnetic fields and material's properties. Basically, this effect causes a polarization rotation of light during its propagation along the magnetic field in a medium. Here, we report an extreme case of the Faraday effect where a linearly polarized ultrashort laser pulse splits in time into two circularly polarized pulses of opposite handedness during its propagation in a highly magnetized plasma. This offers a new degree of freedom for manipulating ultrashort and ultrahigh power laser pulses. Together with technologies of ultra-strong magnetic fields, it may pave the way for novel optical devices, such as magnetized plasma polarizers. In addition, it may offer a powerful means to measure strong magnetic fields in laser-produced plasmas.Comment: 18 pages, 5 figure

Effective suppression of parametric instabilities with decoupled broadband lasers in plasma

A theoretical analysis for the stimulated Raman scattering (SRS) instability driven by two laser beams with certain frequency difference is presented. It is found that strong coupling and enhanced SRS take place only when the unstable regions for each beam are overlapped in the wavenumber space. Hence a threshold of the beam frequency difference for their decoupling is found as a function of their intensity and plasma density. Based upon this, a strategy to suppress the SRS instability with decoupled broadband lasers (DBLs) is proposed. A DBL can be composed of tens or even hundreds of beamlets, where the beamlets are distributed uniformly in a broad spectrum range such as over 10% of the central frequency. Decoupling among the beamlets is found due to the limited beamlet energy and suitable frequency difference between neighboring beamlets. Particle-in-cell simulations demonstrate that SRS can be almost completely suppressed with DBLs under the laser intensity ∼ 1015 W/cm2. Moreover, stimulated Brillouin scattering (SBS) will be suppressed simultaneously with DBLs can be attractive for driving inertial confined fusion

Generation of femtosecond γ-ray bursts stimulated by laser-driven hosing evolution

The promising ability of a plasma wiggler based on laser wakefield acceleration to produce betatron X-rays with photon energies of a few keV to hundreds of keV and a peak brilliance of 1022-1023 photons/s/mm2 /mrad2 /0.1%BW has been demonstrated, providing an alternative to large-scale synchrotron light sources. Most methods for generating betatron radiation are based on two typical approaches, one relying on an inherent transverse focusing electrostatic field, which induces transverse oscillation, and the other relying on the electron beam catching up with the rear part of the laser pulse, which results in strong electron resonance. Here, we present a new regime of betatron γ-ray radiation generated by stimulating a large-amplitude transverse oscillation of a continuously injected electron bunch through the hosing of the bubble induced by the carrier envelope phase (CEP) effect of the self-steepened laser pulse. Our method increases the critical photon energy to the MeV level, according to the results of particle-in-cell (PIC) simulations. The highly collimated, energetic and femtosecond γ-ray bursts that are produced in this way may provide an interesting potential means of exploring nuclear physics in table top photo nuclear reactions

Directional enhancement of selected high-order-harmonics from intense laser irradiated blazed grating targets

Relativistically intense laser solid target interaction has been proved to be a promising way to generate high-order harmonics, which can be used to diagnose ultrafast phenomena. However, their emission direction and spectra still lack tunability. Based upon two-dimensional particle-in-cell simulations, we show that directional enhancement of selected high-order-harmonics can be realized using blazed grating targets. Such targets can select harmonics with frequencies being integer times of the grating frequency. Meanwhile, the radiation intensity and emission area of the harmonics are increased. The emission direction is controlled by tailoring the local blazed structure. Theoretical and electron dynamics analysis for harmonics generation, selection and directional enhancement from the interaction between multi-cycle laser and grating target are carried out. These studies will benefit the generation and application of laser plasma-based high order harmonics

A two-dimensional angular-resolved proton spectrometer

We present a novel design of two-dimensional (2D) angular-resolved spectrometer for full beam characterization of ultrashort intense laser driven proton sources. A rotated 2D pinhole array was employed, as selective entrance before a pair of parallel permanent magnets, to sample the full proton beam into discrete beamlets. The proton beamlets are subsequently dispersed without overlapping onto a planar detector. Representative experimental result of protons generated from femtosecond intense laser interaction with thin foil target is presented

Success Probability Assessment Based on Information Entropy

The Bayesian method is superior to the classical statistical method on condition of small sample test. However, its evaluation results are not so good if subjective prior information is intervened. The success probability assessment about the success or failure tests of weapon products focussed in this paper, and a fusing evaluation method based on information entropy is proposed. Firstly, data from equivalent surrogate tests is converted into the prior information of an equivalent source by the information entropy theory. Secondly, the prior distribution of the success probability is identified via the Bootstrap method, and the posterior distribution is provided by the Bayesian method with the information of prototype tests in succession. Lastly, an example is given, and the results show that the proposed method is effective and valuable.Defence Science Journal, 2010, 60(3), pp.271-275, DOI:http://dx.doi.org/10.14429/dsj.60.35

Quick Construction of Femoral Model Using Surface Feature Parameterization

To facilitate the modifying of femoral surface model, by dividing the femoral mesh into surface feature units bearing medical significance based on surface feature technology, a new approach of constructing femoral models using surface feature technology is proposed. Firstly, considering of femoral anatomy, the femoral triangle mesh model generated from the averaged point-clouds is divided into several specific regions, which are called feature regions; Secondly, feature parameters are defined and the constraints among them are set up, and feature surfaces are created by skinning the contours; Finally, the adjacent feature surfaces are connected by transition surfaces, and the parametric CAD surface model of femur is constructed. Experimental results show that, with the proposed method, the surface feature model can be intuitively constructed and edited with high-level parameters. Therefore, the proposed method provides a basic tool for the design of implants and the digital restoration of incomplete femurs

Very Compact Linear Colliders Comprising Seamless Multistage Laser-Plasma Accelerators

A multistage laser-plasma accelerator (LPA) driven by two mixing electromagnetic hybrid modes of a gas-filled capillary waveguide is presented. Plasma wakefields generated by a laser pulse comprising two mixing modes coupled to a metallic or dielectric capillary filled with gas provide us with an efficient accelerating structure of electrons in a substantially long distance beyond a dephasing length under the matching between a capillary radius and plasma density. For a seamless multistage structure of the capillary waveguide, the numerical model of the transverse and longitudinal beam dynamics of an electron bunch considering the radiation reaction and multiple Coulomb scattering effects reveals a converging behavior of the bunch radius and normalized emittance down to ∼1 nm level when the beam is accelerated up to 560 GeV in a 67 m length. This capability allows us to conceive a compact electron-positron linear collider providing with high luminosity of 1034 cm−2 s−1 at 1 TeV center-of-mass (CM) energy