中枢神経系疾患の治療は正常細胞（ニューロン）の機能維持を目的とするが，脳血管障害のように機能障害の原因が細胞の死滅に基づくことは多い．一方，脳腫瘍の治療においては薬物療法や放射線療法といった腫瘍細胞の死滅を目標とするものが大きな位置を占める．いずれの場合にも，細胞死の機序を理解することは各種病態や治療法の理解のうえで重要である．現在のところ最も研究の進んでいる細胞死の型はアポトーシスである．そのなかで重要な位置を占めるミトコンドリアにおける反応および抗アポトーシス因子について概要を紹介する．

Neuroscience 細胞死：最近の知見

The advent of ultraintense laser pulses generated by the technique of chirped pulse amplification (CPA) along with the development of high-fluence laser materials has opened up an entirely new field of optics. The electromagnetic field intensities produced by these techniques, in excess of ${10}^{18}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$, lead to relativistic electron motion in the laser field. The CPA method is reviewed and the future growth of laser technique is discussed, including the prospect of generating the ultimate power of a zettawatt. A number of consequences of relativistic-strength optical fields are surveyed. In contrast to the nonrelativistic regime, these laser fields are capable of moving matter more effectively, including motion in the direction of laser propagation. One of the consequences of this is wakefield generation, a relativistic version of optical rectification, in which longitudinal field effects could be as large as the transverse ones. In addition to this, other effects may occur, including relativistic focusing, relativistic transparency, nonlinear modulation and multiple harmonic generation, and strong coupling to matter and other fields (such as high-frequency radiation). A proper utilization of these phenomena and effects leads to the new technology of relativistic engineering, in which light-matter interactions in the relativistic regime drives the development of laser-driven accelerator science. A number of significant applications are reviewed, including the fast ignition of an inertially confined fusion target by short-pulsed laser energy and potential sources of energetic particles (electrons, protons, other ions, positrons, pions, etc.). The coupling of an intense laser field to matter also has implications for the study of the highest energies in astrophysics, such as ultrahigh-energy cosmic rays, with energies in excess of ${10}^{20}\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The laser fields can be so intense as to make the accelerating field large enough for general relativistic effects (via the equivalence principle) to be examined in the laboratory. It will also enable one to access the nonlinear regime of quantum electrodynamics, where the effects of radiative damping are no longer negligible. Furthermore, when the fields are close to the Schwinger value, the vacuum can behave like a nonlinear medium in much the same way as ordinary dielectric matter expanded to laser radiation in the early days of laser research.

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Optics in the relativistic regime

The field of laser-matter interaction traditionally deals with the response of atoms, molecules, and plasmas to an external light wave. However, the recent sustained technological progress is opening up the possibility of employing intense laser radiation to trigger or substantially influence physical processes beyond atomic-physics energy scales. Available optical laser intensities exceeding ${10}^{22}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$ can push the fundamental light-electron interaction to the extreme limit where radiation-reaction effects dominate the electron dynamics, can shed light on the structure of the quantum vacuum, and can trigger the creation of particles such as electrons, muons, and pions and their corresponding antiparticles. Also, novel sources of intense coherent high-energy photons and laser-based particle colliders can pave the way to nuclear quantum optics and may even allow for the potential discovery of new particles beyond the standard model. These are the main topics of this article, which is devoted to a review of recent investigations on high-energy processes within the realm of relativistic quantum dynamics, quantum electrodynamics, and nuclear and particle physics, occurring in extremely intense laser fields.

Extremely high-intensity laser interactions with fundamental quantum systems

http://absimage.aps.org/image/DAMOP12/MWS_DAMOP12-2012-000066.pdf

Optics in the Relativistic Regime

Acceleration of relativistic electrons in a dielectric laser accelerator at high electric field gradients is reported, setting the stage for the development of future multi-staged accelerators of this type. Conventional particle accelerators, based on radio-frequency technology, are large-scale installations that are expensive to run. Micro-fabricated dielectric laser accelerators (DLAs) offer an attractive alternative, as they are able to support much larger accelerating fields than current accelerators, while being compact, economical and simple to manufacture using lithographic techniques. This paper presents the first experimental demonstration of a DLA capable of sustained, high-gradient (beyond 250 MeV m−1) acceleration of relativistic electrons. The results set the stage for the development of future multi-staged DLA devices composed of integrated on-chip systems, which would enable compact table-top MeV–GeV-scale accelerators. Applications include security scanners and medical therapy, X-ray light sources for biological and materials research, and portable medical imaging devices. The enormous size and cost of current state-of-the-art accelerators based on conventional radio-frequency technology has spawned great interest in the development of new acceleration concepts that are more compact and economical. Micro-fabricated dielectric laser accelerators (DLAs) are an attractive approach, because such dielectric microstructures can support accelerating fields one to two orders of magnitude higher than can radio-frequency cavity-based accelerators. DLAs use commercial lasers as a power source, which are smaller and less expensive than the radio-frequency klystrons that power today’s accelerators. In addition, DLAs are fabricated via low-cost, lithographic techniques that can be used for mass production. However, despite several DLA structures having been proposed recently1,2,3,4, no successful demonstration of acceleration in these structures has so far been shown. Here we report high-gradient (beyond 250 MeV m−1) acceleration of electrons in a DLA. Relativistic (60-MeV) electrons are energy-modulated over 563 ± 104 optical periods of a fused silica grating structure, powered by a 800-nm-wavelength mode-locked Ti:sapphire laser. The observed results are in agreement with analytical models and electrodynamic simulations. By comparison, conventional modern linear accelerators operate at gradients of 10–30 MeV m−1, and the first linear radio-frequency cavity accelerator was ten radio-frequency periods (one metre) long with a gradient of approximately 1.6 MeV m−1 (ref. 5). Our results set the stage for the development of future multi-staged DLA devices composed of integrated on-chip systems. This would enable compact table-top accelerators on the MeV–GeV (106–109 eV) scale for security scanners and medical therapy, university-scale X-ray light sources for biological and materials research, and portable medical imaging devices, and would substantially reduce the size and cost of a future collider on the multi-TeV (1012 eV) scale.

https://web.stanford.edu/~rlbyer/PDF_AllPubs/2013/Nature%20Final%20Version.pdf

Demonstration of electron acceleration in a laser-driven dielectric microstructure

The use of infrared lasers to power optical-scale lithographically fabricated particle accelerators is a developing area of research that has garnered increasing interest in recent years The physics and technology of this approach is reviewed, which is referred to as dielectric laser acceleration (DLA) In the DLA scheme operating at typical laser pulse lengths of 01 to 1 ps, the laser damage fluences for robust dielectric materials correspond to peak surface electric fields in the $\mathrm{GV}/\mathrm{m}$ regime The corresponding accelerating field enhancement represents a potential reduction in active length of the accelerator between 1 and 2 orders of magnitude Power sources for DLA-based accelerators (lasers) are less costly than microwave sources (klystrons) for equivalent average power levels due to wider availability and private sector investment Because of the high laser-to-particle coupling efficiency, required pulse energies are consistent with tabletop microJoule class lasers Combined with the very high (MHz) repetition rates these lasers can provide, the DLA approach appears promising for a variety of applications, including future high-energy physics colliders, compact light sources, and portable medical scanners and radiative therapy machines

Dielectric laser accelerators

We review recent progress in the physics and technology of cold cathode electron emitters. The characteristics of emission from field emitter arrays, photocathodes, and ferroelectrics are presented, together with a summary of the understanding of the physics involved. The paper concludes with a description of L-band micropulse gun, based on secondary emission in an RF cavity. Emphasis is placed on cathode development for electron guns to drive microwave tubes and RF accelerators.

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Advances in cold cathode physics and technology

It is demonstrated that a Bragg waveguide consisting of a series of dielectric layers may form an excellent optical acceleration structure. Confinement of the accelerating fields is achieved, for both planar and cylindrical configurations by adjusting the first dielectric layer width. A typical structure made of silica and zirconia may support gradients of the order of $1\phantom{\rule{0.3em}{0ex}}\text{GV}∕\mathrm{m}$ with an interaction impedance of a few hundreds of ohms and with an energy velocity of less than $0.5\mathrm{c}$. An interaction impedance of about $1000\phantom{\rule{0.3em}{0ex}}\ensuremath{\Omega}$ may be obtained by replacing the Zirconia with a (fictitious) material of $\ensuremath{\epsilon}=25$. Special attention is paid to the wake field developing in such a structure. In the case of a relatively small number of layers, it is shown that the total electromagnetic power emitted is proportional to the square of the number of electrons in the macrobunch and inversely proportional to the number of microbunches; this power is also inversely proportional to the square of the internal radius of the structure for a cylindrical structure, and to the width of the vacuum core in a planar structure. Quantitative results are given for a higher number of dielectric layers, showing that in comparison to a structure bounded by metallic walls, the emitted power is significantly smaller due to propagation bands allowing electromagnetic energy to escape.

/pdf/optical-bragg-accelerators-2kmwna0vek.pdf

Optical Bragg accelerators.

This text is primarily concerned with the interaction of electrons with electromagnetic waves for the generation and amplification of radiation. It dicusses the various methods of electron-beam generation and propagation and the basic electron-wave interaction schemes, then it presents an idealized picture of the beam-wave interaction in a dielectric loaded waveguide. Gradually the complexity of the analysis is increased by presenting the effect of reflected waves and further by considering the beam as an ensemble of macro-particles. The book also dicusses the interaction in periodic and in quasi-periodic metallic structures and the fundamentals of the beam-wave interaction in a periodic field, concluding with a brief discussion of particle acceleration, including novel acceleration schemes.

Beam-Wave Interaction in Periodic and Quasi-Periodic Structures

A 1 kW hybrid microwave system was fabricated using a partially oxidized SiC powder bed and used to sinter small components of low-loss insulating ceramics. Samples of 3% yttria stabilized zirconia/20% alumina (3YZA) and 99% alumina were sintered to final densities of 99%(3YZA) and 95%(99% alumina). Partially oxidized silicon carbide (β-SiC) powder was used as susceptor (preheater). By comparison, unoxidised β-SiC powder, which couples well with microwaves at room temperature, exhibited thermal runaway above 400°C. It could be possible that at high oxidation levels the connectivity between SiC particles in β-SiC powder bed might become depercolated, and a model similar to one proposed for silicon nitridation under microwaves could be appropriate in understanding the microwave absorption phenomenon. Stable temperature measurements at various positions in the system confirmed that the maximum temperature was at the center of the 3YZA sample. The plot of the relative temperature difference between the sample and its surroundings as a function of sample temperature resulted in a bell-shaped curve with a clear maximum at around 800°C, associated with the rapid increase in radiation heat transfer above this temperature. Experiments also confirmed that sintering occurred at lower temperatures in a microwave field when compared to conventional sintering.

/pdf/use-of-partially-oxidized-sic-particle-bed-for-microwave-1ekkved78i.pdf

Levi Schächter

Papers

Dielectric laser accelerators

Advances in cold cathode physics and technology

Optical Bragg accelerators.

Beam-Wave Interaction in Periodic and Quasi-Periodic Structures

Use of partially oxidized SiC particle bed for microwave sintering of low loss ceramics