Radiation Generation and Particle Acceleration using Photonic Crystal

光子带隙晶体是具有不同衍射率的规则排列的材料。它们的晶格常数可以在激光波长的数量级上。为了将这种晶体应用于加速器，进行了两个实验。一个是史密斯-珀塞尔辐射产生。如果电子束在晶格常数范围内平行于晶格面运行，就可以产生这种辐射。实验使用了大学实验室制造的二维晶体和大阪大学isir的35 MeV直线加速器。我们预计其(k，ω)特性对应于晶体布里渊图上光束色散和带线的交点的辐射。然而，我们观测到的辐射比预期的要多得多。我们认为这主要是因为~5 mm的光束尺寸比晶格大得多，约1μm。另一个实验是利用激光器的纵向电场来加速电子。如果激光脉冲的波长在晶体的带隙内，则光子晶体光纤的纤芯引导激光脉冲。纵向场支撑在光纤芯中。用水晶纤维公司的产品AIR-800光纤实验产生了高达2 MeV电子的700GW 800 nm 50fs激光脉冲。对于800 nm激光，光纤的透明度是目录上数值的约1/10。加速度梯度比计算值小3个数量级。

Photonic band-gap crystals are regular array of materials with different diffractive indices. Their lattice constants can be on the order of laser wavelengths. Two experiments were performed which try to apply the crystals to accelerators.One is the Smith-Purcell radiation generation. It is expected that electron beams can generate this radiation if they run parallel to the lattice surface within the distance of the lattice constant. Experiments used a two-dimensional crystal manufactured in the university laboratory and the 35MeV linac of ISIR, Osaka University. We expected the radiation whose (k,ω) characteristics corresponding to the intersection of beam dispersion and band lines on the Brillouin diagram of the crystal. We, however, observed much more radiations than expected. We consider that this is mainly because the beam size, 〜5mm, was much larger than the crystal lattice, <1μm.Another experiment is the acceleration of electrons using longitudinal electric fields of lasers. Core of the photonic crystal fiber guides laser pulses, if their wavelength is in the band-gap of the crystal. The longitudinal fields are supported in the fiber core. A 700GW 800nm 50fs laser pulse experimentally produced up to 2MeV electrons from AIR-800 fiber, product of Crystal Fibre Inc.. The transparency of the fiber for the 800nm laser was 〜1/10 of the value on the catalog. The acceleration gradient was smaller than the calculation by the order of 3.