The features of band structures for woodpile three-dimensional photonic crystals with plasma and function dielectric constituents

The features of the band structures of woodpile three-dimensional (3D) photonic crystals composed of plasma and function dielectric constituents, referred to as function plasma photonic crystals (FPPCs), are theoretically studied by a modified plane wave expansion method, and the formulas for computing the band structures are derived. The arrangement for the proposed FPPCs is that the function dielectric columns are surrounded by plasma, and the embedded dielectric columns are stacked according to the woodpile lattices, which are arrayed with face- centered-tetragonal symmetry. The relative permittivity of function dielectric rods depends on the function coefficient and space coordinates. The relationships between the parameters for inserted function dielectric rods and plasma and the band structures are also investigated. The computed results illustrate that the obtained PBG can be tuned by those parameters as mentioned above. Compared to dielectric–air PCs, function dielectric PCs and plasma dielectric PCs with the same topology, a wider bandwidth of the photonic band gap can be observed in the proposed FPPCs. The calculated results also show us another alternative way to realize reconfigurable applications with 3D FPPCs.     

Model for X-ray Cherenkov radiation by MeV electrons at grazing incidence

A possible source of radiation in the X-ray range can be obtained by penetration of a dielectric slab by electrons with sufficient kinetic energy. We present a near-exact solution of Maxwell equations to obtain the intensity of Cherenkov (and transition) radiation from slabs thicker than the absorption length, the only approximation being that the observation angle of the radiation with respect to the electron axis is taken to be small. Contrary to earlier models our model accounts for all relativistic electron energies, dielectric constants and grazing incidence angles. Also scattering of the electrons is incorporated very accurately, including the effect of scattering on the electro-magnetic fields within the slab. We report significant differences with earlier calculation for radiation yields from e.g. Si. A new effect has been found for intermediate angles of incidence (around 45°). At these angles, the cone of Cherenkov radiation exhibits pronounced minima near the direction perpendicular to the plane of incidence. We present arguments based on the special characteristics of Cherenkov radiation why in that direction internal reflection of the radiation occurs at the medium-vacuum interface.     

Effects of Pulsed Ionizing Radiation on Some Selected Quartz Oscillator Crystals

The effects of high-energy ionizing radiation on the behavior and output frequency of electronic oscillators, whose frequency-determining elements were quartz crystals operating in the vicinity of 5 Mc, have been studied. Both fundamental- and fifth-overtone crystals were studied over a dose range from 3,000 rads (Si) to 2 Mrads (Si). The crystals studied were of two types: (1) standard commercial precision crystals fabricated from natural quartz with Q's of approximately 2.5 × 106 for the fifth overtone and 4 × 105 for the fundamental, and (2) special fifth-overtone crystals fabricated from swept pure Z-growth synthetic quartz. The natural quartz showed much larger changes in frequency and transient loss of Q than the swept synthetic crystals. The crystals were incorporated into commercial precision oscillator circuits and maintained in a temperature-controlled oven. The radiation doses (both 25-MeV electrons and 10-MeV peak bremsstrahlung gamma rays) were provided by the General Atomic electron linear accelerator. The radiation was collimated to irradiate only the crystal. The oscillator output signal was monitored with an oscilloscope during and after the radiation burst, and the frequency was measured by cycle counting for 10-or 100-sec time intervals. The precision of the frequency measurements was ±2 parts in 108 for the 10-sec intervals and ±2 parts in 109 for the 100-sec intervals. Electrons and gamma rays were shown to have the same effect on the crystals; therefore, most of the work was done with electrons because of the convenience of accumulating large doses in 4.5-psec pulses.     

A method to measure transit time spread of photomultiplier tubes with Cherenkov light

With the technology of coincidence method, transit time spreads (TTSs) of PMTs are measured with Cherenkov light on the photocathode window of photomultiplier tube (PMT) produced by cascade γ radiation source,~(60)Co. TTSs with single and multi-photoelectron which are analyzed by convolution of Poisson and Gaussian are obtained. The study to XP2020 and XP2020Q PMTs shows that TTSs are consistent with data supplied by Philips.TTSs are inversely proportional to the square roots of number of photoelectrons. The method is feasible when single and multi-photoelectron can be distinguished.     

Valley-dependent topological edge states in plasma photonic crystals

Plasma photonic crystals designed in this paper are composed of gas discharge tubes to control the flow of electromagnetic waves.The band structures calculated by the finite element method are consistent with the experimental results which have two distinct attenuation peaks in the ranges of 1-2.5 GHz and 5-6 GHz.Electromagnetic parameters of the plasma are extracted by the Nicolson-Ross-Weir method and effective medium theory.The measured electron density is between 1 × 10¹¹ cm^-...     

Disorder effects in reflectance spectra of colloidal photonic crystals

Although fabrication of photonic crystals improved over the last few years, intrinsic defects of the crystal lattice affect the experimentally measured spectral features. In order to compare experimental spectra with simulated photonic band structure, disorder effects are simulated by introduction of material absorption. By using the finite-difference time-domain (FDTD) method we were able in the past to obtain a good agreement between experimental and simulated transmission curves by taking in account the glass substrate. In this work we extend our analysis for reflectance curves of one, two and three-layered close-packed polystyrene spheres. We show that a key ingredient in simulating disorder effects is the introduction of fictional absorption for polystyrene.     

Angular distribution of radiation by relativistic electrons in a thin crystal

The results of theoretical investigation of angular distributions of radiation from a relativistic electron passing through a thin crystal at a small angle to the crystal axis are presented. The electron trajectories in crystal were simulated using the binary collision model which takes into account both coherent and incoherent effects at scattering. The angular distribution of radiation was calculated as a sum of radiation from each electron. It is shown that there are non-trivial angular distributions of the emitted photons, which is connected to the superposition of the coherent scattering of electrons by atomic rows (“doughnut scattering” effect) and the suppression of the radiation due to the multiple scattering effect (similar to the Landau–Pomeranchuk–Migdal effect in an amorphous matter). The orientation dependence of angular distribution of radiation is also analyzed.     

Numerical study on the modulation of THz wave propagation by collisional microplasma photonic crystal

In order to demonstrate the modulation of terahertz wave propagation in atmospheric pressure microplasmas, in this work, the band structure and the transmission characteristics of a onedimensional collisional microplasma photonic crystal are investigated, using the transfer matrix method. For a lattice constant of 150 μm and a plasma width of 100 μm, three stopbands of microplasma photonic crystal are observed, in a frequency range of 0.1–5 THz. Firstly, an increase in gas pressure leads to a decrease in the central frequency of the stopband. When the gas pressure increases from 50.5 kPa to 202 kPa, the transmission coefficient of the THz wave first increases and then decreases at high frequency, where the wave frequency is much greater than both the plasma frequency and the collision frequency. Secondly, it is interesting to find that the central frequency and the bandwidth of the first THz stopband remain almost unchanged for electron densities of less than 10¹⁵ cm^–3, increasing significantly when the electron density increases up to 10¹⁶ cm^–3. A central frequency shift of 110 GHz, and a bandgap broadening of 200 GHz in the first stopband are observed. In addition, an atmospheric pressure microplasma with the electron density of 1 × 10¹⁵–6 × 10¹⁵ cm^–3 is recommended for the modulation of THz wave propagation by plasma photonic crystals.     

The Absorbing Properties of Two-Dimensional Plasma Photonic Crystals

Plasma photonic crystals composed of periodic plasma and dielectric materials have attracted considerable attention because of their tunable photonic band gaps,but only their band structures or negative refractive index properties have been addressed in previous works.In this paper,through studying the transmission and reflection characteristics of two types of twodimensional plasma photonic crystals,it is found that plasma photonic crystals play an important role in absorbing waves,and they show broader band and higher amplitude absorption characteristics than bulk plasmas.Also,the absorption of plasma photonic crystals can be tuned via plasma parameters;varying the collision frequency can make the bandwidth and amplitude tunable,but cannot change the central frequency,whereas varying the plasma frequency would control both the location and the amplitude of the absorbers.These features of plasma photonic crystals have potential for terahertz tunable absorber applications.     

PET复合晶体甄别电子学及算法设计

设计并实现了一种高分辨率复合晶体探测器和电子学,并提出一种系统辨识的算法。复合晶体探测由LYSO(Lu2-xYxSiO5)和YSO(Y2SiO5)两种晶体交错排列而成,目的在于提高晶格的定位能力,改善空间分辨率。由甄别电路完成对PMT(photomultiplier tube)原始信号的处理,使用了高速ADC对信号连续采样,由FPGA完成波形采集,并能够完成实时基线恢复。甄别算法是分析了探测器响应和电子学采集模型之后提出的,是一种系统辨识算法。晶体甄别是基于提取与信号的衰减时间常数相关量来完成的。对LYSO和YSO的单晶体条实验,其甄别率超过98%;并绘制了甄别后两种晶体的二维直方图(2Dmap),有效地减少晶格间交叠,提高了空间分辨率。     

BSRF高灵敏度衍射增强成像系统搭建

作为一种重要的相位衬度成像方法,衍射增强成像(Diffraction Enhanced Imaging,DEI)是利用晶体的角度选择特性探测样品引起的X射线角度变化来获得样品衬度图像。晶体摇摆曲线是衍射增强成像装置的重要特征,理论上晶体的摇摆曲线越窄,则衍射增强成像灵敏度越高,所获得的图像衬度也会越好。在北京同步辐射装置(Beijing Synchrotron Radiation Facility,BSRF)4W1A成像实验站现有Si(111)晶体DEI装置的基础上,通过选用高精度转台并对晶体采取减少加工应力残余和降低安装夹持应力的措施,设计研制了基于Si(400)和Si(333)晶体的高灵敏度DEI实验装置,并利用标准样品和实际生物样品进行了实验验证。系统摇摆曲线测试及成像结果表明,所研制的成像装置可以开展二维和三维成像实验且具有更高的成像灵敏度。     

Cherenkov radiation from relativistic heavy ions taking account of their slowing down in radiator

Combining the SRIM’06 computer code and the formula for spectral-angular distribution of radiation from a particle moving in a medium in arbitrary trajectory, we studied numerically the structure of angular distributions of Cherenkov radiation from moderately relativistic heavy ions (RHI) taking into account the decrease of the ion velocity due to stopping in the radiator. The results obtained clearly show that the width and the fine structure of the Cherenkov radiation in the vicinity of the Cherenkov cone depend strongly on several factors, e.g. the mean and total energy losses, the radiator thickness, the square of the ion charge, the emission wavelength and the refractive index of the radiator material. This might be useful for experiments using RICH detectors for relativistic heavy ions.     

Microwave transmittance characteristics in different uniquely designed one-dimensional plasma photonic crystals

Plasma photonic crystals(PPCs) are emerging as a powerful instrument for the dynamical control of the electromagnetic properties of a propagating wave. Here we demonstrate several one-dimensional(1 D) PPCs with uniquely designed superlattice structures, annular structures or with incorporation of the third material into the primitive unit cell. The influences of the properties of the third material as well as the structural configurations of suplerlattices on the transmittance characteristics of PPCs have been investigated by use of the finite element method.The optimal design strategy for producing PPCs that have more and larger band gaps is provided. These new schemes can potentially be extended to 2 D or 3 D plasma crystals, which may find broad applications in the manipulation of microwaves and terahertz waves.     

Effect of Irradiation on Crystal Defects in Quartz

X-and ?-irradiation characteristics of optically non-clear natural quartz and electronic grade synthetic crystals have been investigated. In particular, it has been shown how, due to relatively large concentration of crystal imperfections in non-clear natural quartz, a positive frequency shift of crystal resonator on extended irradiation, increased smoky coloration, broad and sharp ESR signals observable at room temperature and increased intensity of thermoluminescence are produced compared to the corresponding characteristics of optically clear quartz crystals. It has been shown, how by increasing the imperfections in non-clear natural quartz still further by neutron irradiation, the frequency characteristics of natural quartz crystals would simulate those of the electronic grade synthetic crystals, and viceversa, by thermal annealing of the latter. Based on the appropriate thermal annealing of electronic grade synthetic crystals, the investigations yield a new way of achieving the much desired radiation hardening of quartz resonators used in satellite-borne frequency standards for space communication.     

Atom probe study of radiation induced grain boundary segregation/depletion in a Fe-12%Cr alloy

Ferritic steels are important candidate structural materials for future fission and fusion reactors. However, the effect of radiation induced segregation/depletion (RIS/RID) of Cr in grain boundaries and its effect on microstructures and properties are still not clear. Therefore, a systematic approach is shown in this paper, combining electron backscattered diffraction, focused ion beam specimen preparation and atom probe tomography for analysing a single grain boundary in a Fe-12wt%Cr from the point of grain boundary orientation, microchemistry and impurities. Several samples have been prepared from the same grain boundary and consistent 3D reconstruction with quantitative calculation of segregation demonstrates the high reliability and repeatability of this approach.     

Coherent electron radiation in a synchrotron

The coherent radiation of electrons in a synchrotron was investigated experimentally for a wavelength of 10 cm, corresponding to the 50th harmonic of the electron frequency of revolution for various electron distributions inside the separatrix. In most cases, the theory of coherent radiation of electrons is confirmed. A disparity with the theory is observed for almost uniform electron distributions. The radiation was used for measurements of the electron phase oscillations and adiabatic damping of the phase oscillation amplitudes. The experiment was carried out on the synchrotron at the Physics Institute, Academy of Sciences, USSR at 280 Mev with an initial betratron acceleration.In conclusion, the authors thank Prof. P. A. Cherenkov, Prof. M. S. Rabinovich, Prof. A. M. Prkhorov, and L. V. Iogansen for valuable discussions.     

8 MeV electron irradiation effect on the dielectric and optical properties of iminodiacetic acid doped ferroelectric triglycine sulphate crystals

Single crystal of iminodiacetic acid (5 mol%) doped Tri Glycine Sulphate (IDATGS) was grown by slow evaporation from its aqueous solution at constant temperature, using solution growth method. The dielectric constant (ε′) and pyroelectric current (I_P) were measured over the temperature range of 30-60 °C in the ferroelectric direction. The measured values of ε′ and I_P were found to be smaller compared to pure triglycine sulphate (TGS) crystal parameters. But increased transition temperature was observed for doped crystals. Curie Weiss constants C_P and C_f in the paraelectric and ferroelectric phases were also determined. The doped crystal was irradiated with graded dosages from 5 to 80 kGy of electron beam from 8 MeV Microtron at room temperature and radiation effects on optical and dielectric properties were studied. The UV-Vis absorption spectrum indicates that the UV lower cutoff shifts towards the higher wavelength region (red shift) and the optical band gap is found to be decreasing with the increase of electron dose. It is also observed that the electron irradiation effects in pure and doped TGS were found to be long lasting. The dielectric study shows that there is a gradual reduction in dielectric constant at T_C and shifting of Curie temperature towards lower temperature region with the increase in electron radiation dose. The material figures of merit were found increased after the crystal was irradiated. Induced changes in the physical and optical properties due to irradiation may help one to tailor the device quality and characteristics.     

Monochromatic X-ray sources based on a mechanism of real and virtual photon diffraction in crystals

A source of monochromatic X-ray radiation is wanted in industry, science, medicine and so on. Many ways of making such a source are known. The present work describes two mechanisms for the creation of a monochromatic X-ray beam, which are parametric X-ray radiation (PXR) and bremsstrahlung diffraction (DBS). Both the experiments were carried out using an electron beam at a microtron. During the first experiment, the DBS process was investigated as a scattering of the Bremsstrahlung (BS) beam on the crystallographic surfaces of tungsten and pyrolytic graphite crystals. The second experiment consisted in the registration of the PXR and DBS yield during the passage of the electrons through the same crystals as in the first experiment. The spectral and orientation radiation characteristics and simulation results obtained for the DBS and PXR processes are presented. It is shown that the usage of mosaic crystalline targets is rather useful in order to obtain a monochromatic X-ray source based on bremsstrahlung diffraction from moderately relativistic electrons.     

The bremsstrahlung spectrum of electrons with an energy of 260 Mev

The bremsstrahlung spectrum of electrons with an energy of 260 Mev was measured experimentally with a 15-channel gamma-ray pair spectrometer. A considerable difference was observed between the experimental spectrum and the Schiff spectrum [1] in the photon energy range near the maximum. It was shown that for target thicknesses equal to approximately 0.10 radiation unit it is even more important to take into consideration the multiple emission of photons by one electron.In conclusion, the authors express their thanks to Professor P. A. Cherenkov for his valuable comments, as well as to Engineer M. P. Piskov and Technician Yu. I. Krutov for their important work in the construction of the apparatus.     

Angular distributions of Diffracted Channeling Radiation from moderate energy axially channeled electrons in Si and LiF crystals

Numerical calculations of the Diffracted Channeling Radiation angular distributions from axially channeled electrons with relativistic factor γ = 20 in Si and LiF crystals are performed. The calculations are based on a newly developed effective quantum-mechanical calculations algorithm of the wave functions and electron energies at axial channeling in a crystal. The numerical results obtained exhibit some new features of the Diffracted Channeling Radiation from axially channeled electrons compared to that from planar channeled electrons, e.g. increase of the widths of peaks, which might be useful in future experiments on observation of Diffracted Channeling Radiation.