反射三次谐波产生与晶体对称性

在单晶硅和经离子注入的硅样品上测得了反射三次谐波。像我们的理论计算中所证明的那样,当样品绕表面法线转动时,线偏振的三次谐波强度显示了晶体的旋转对称性,对于轻注入的样品,存在一个注入剂量的临界值,高于此值,三次谐波信号与转动无关。作为剂量的函数,三次谐波强度对晶格损伤极为敏感。这使三次谐波技术可以在半导体工艺中用作监测离子注入的均匀程度。 关键词：     

Femtosecond laser plasma in CaF<Subscript>2</Subscript> crystal microchannel and effective generation of characteristic X-ray radiation

The dependence of the characteristic X-ray radiation yield from CaF₂ crystal on the formed microchannel depth under highly intensive (I ∼ 3 × 10¹⁵ W/cm²) laser pulses with different contrast was obtained. The maximum of the characteristic X-ray radiation yield at these experimental conditions corresponded to the microchannel depth of 30–50 μm. The efficiency of the laser radiation conversion to the characteristic X-ray radiation increased from 6 × 10⁻⁸ for the surface up to 10⁻⁷ in the microchannel. The dependence of the characteristic X-ray radiation yield on the viewing angle showed that the source of X-ray radiation was located near the surface inside the microchannel.     

Photon emission under bombardment of ruby by ions and electrons of medium energies

The characteristics of optical radiation produced under bombardment by ions (1–15 keV) and electrons (100–1000 eV) of a ruby surface are studied. Two broad bands with maxima at 330 and 450 nm attributed to defects of the crystal lattice are discovered in the spectral region of 200 to 800 nm. Characteristic radiation related to radiative relaxation of excited Cr³⁺ ions in the near-surface region of the crystal is observed. The dependence of the radiation intensity on the energy and current density of the bombarding particles is obtained experimentally. The degree of radiation polarization is determined.     

Generation of X-ray radiation at the interaction of protons with dielectrics

Properties of the characteristic X-ray radiation excited in quartz under 100-keV proton bombardment have been experimentally investigated. The measured intensity of SiK _α radiation for quartz is higher than that for pure silicon by three orders of magnitude. An afterglow from the target is observed for hundreds of seconds after the ion beam is turned off. This enhanced radiation intensity and the afterglow duration have been measured as a function of the beam current, beam grazing angle, and pressure in the chamber. The measurement data indicate that the enhanced insulator radiation is caused by the accumulation and discharge of a positive charge formed in a dielectric and on its surface under exposure to an ion beam.     

Influences of Mg^2＋ ion on dopant occupancy and upconversion luminescence of Ho^3＋ ion in LiNbO3 crystal

The effects of a Mg^2＋ ion on the dopant occupancy and upconversion luminescence of a Ho^3＋ ion in LiNbO3 crystal are reported. The birefringence gradient of the crystal is measured to investigate the optical homogeneity. The X-ray powder diffraction spectrum and the upconversion luminescence are used to investigate defect structure and spectroscopic properties of Mg,Ho：LiNbO3. Under 808-nm excitation, blue, red, and very intense yellow-green bands are observed. Based on the energy levels of Ho^3＋ in LiNbO3, and the pump intensity dependence of the observed emission, an excitation scheme is presented. The upconversion emission spectra reveal an enhancement of upconversion intensity when the Mg^2＋ ions are introduced into Ho：LiNbO3. The main upconversion mechanism is discussed in this work.     

Observation of parametric X-rays produced by 400 GeV/c protons in bent crystals

Spectral maxima of parametric X-ray radiation (PXR) produced by 400 GeV/c protons in bent silicon crystals aligned with the beam have been observed in an experiment at the H8 external beam of the CERN SPS. The total yield of PXR photons was about 10⁻⁶ per proton. Agreement between calculations and the experimental data shows that the PXR kinematic theory is valid for bent crystals with sufficiently small curvature as used in the experiment. The intensity of PXR emitted from halo protons in a bent crystal used as a primary collimator in a circular accelerator may be considered as a possible tool to control its crystal structure, which is slowly damaged because of irradiation. The intensity distribution of PXR peaks depends on the crystal thickness intersected by the beam, which changes for different orientations of a crystal collimator. This dependence may be used to control crystal collimator alignment by analyzing PXR spectra produced by halo protons.     

Estimation of crystal sample structure by means of fast electron radiation

The dependence of the characteristics of X-ray radiation occurring under fast electron transmission through a crystal on a sample structure has been analyzed. A method to estimate the size of the crystal microblocks by means of the yield ratio of the parametric X-ray radiation and diffracted bremsstrahlung and transition radiation for different observation angles has been suggested. The possibility of estimating the dimension of the microblocks using the ratio of the intensities of these emission mechanisms for the same observation angle and several reflection orders has been discussed.     

激光产生等离子体辐射X射线特性研究

本文报导激光等离子体辐射Ｘ射线的测量方法和结果。在“星光”装置上,用１．６μｍ激光辐照Ｎａ／Ｆ和铜靶。用平晶谱仪测量等离子体辐射Ｘ射线绝对强度,并研究了辐射Ｘ射线强度与入射激光功率密度的关系,测量了靶前后辐射强度之比,为光电离机制的Ｘ光激光研究提供了较重要的数据。     

X-ray diffraction in KDP crystal in the presence of temperature gradient

We investigate the effect of temperature gradient on the intensity of X-ray radiation reflected from different atomic planes of a KDP crystal, depending on the crystal thickness. We have studied the phenomenon of transfer of the X-ray beam intensity for x- and z-cuts of the KDP crystal in the presence and in the absence of temperature gradient. It is shown that the intensities of reflected radiations do not saturate because in conditions of the experiment the further increase in temperature gradient leads to destruction of the sample. It is revealed that in some cases at small values of temperature gradient the intensity of reflected radiation decreases initially by more than 10%, then increases monotonically with the increase in temperature gradient.     

Interference absorption coefficient of X-rays in crystals in the presence of temperature gradient

We investigate experimentally and theoretically the behavior of the interference coefficient of absorption of X-ray radiation of a quartz single crystal in Laue geometry in the presence of temperature gradient. The total intensity of transmitted X-ray radiation and that reflected from different families of reflecting atomic planes of the quartz single crystal has been recorded. It was shown that with the increase in temperature gradient the coefficient of absorption of X-ray radiation decreases abruptly reaching its minimal value at a certain value of the temperature gradient.     

Polarization of photons emitted in the process of resonant coherent excitation of relativistic ions under planar channeling conditions

Owing to the recent observation of the strong anisotropy of characteristic X-ray radiation accompanying the resonant coherent excitation of relativistic Fe²⁴⁺ ions under planar channeling conditions in a silicon crystal, the resonant coherent excitation method can be considered as a candidate for a source of polarized X-ray radiation. The Stokes parameters of the radiation have been calculated using the density matrix approach. The behavior of the polarization characteristics of the radiation in various directions has been explained by considering the properties of the resonance part of the crystal field, which excites an ion and has the form of an elliptically polarized electric field.     

高能X射线聚焦组合透镜的理论研究

X射线聚焦组合透镜是一种利用折射效应对X射线辐射聚焦的新型元件。针对X射线波段的特性,综合考虑折射和吸收效应得出组合透镜的衍射屏函数,并利用衍射理论推导出X射线组合透镜的设计理论。利用统计学理论中一阶、二阶原点矩表征像面处的光学性能,使设计更简洁。该理论方法可方便地推广到双凹折射单元情况。通过数值计算分析了像向处强度分布的二阶中心矩以及焦点处辐射强度随组合透镜结构参最的变化关系,给出了一种铝基X射线组合透镜的结构参量设计结果。对于设计的组合透镜结构参量,计算了当X射线辐射能量分别为0．93 keV．9．89 keV和29．78 keV时,X射线辐射经过组合透镜后的焦点强度分布。     

Excitation of nonlinear surface electromagnetic waves in the prism-metal film-nematic liquid crystal system

The excitation of nonlinear p-polarized surface electromagnetic waves (SEW) in prism-metal film-nematic liquid crystal (NLC) attenuated total reflection (ATR) systems (Kretschmann ATR system) has been investigated both theoretically and experimentally. The third-order optical nonlinearity of the NLC (the only nonlinear medium in our system) has been estimated by measuring the dependence of the reflectance minimum on the incident radiation intensity. The nonlinear optical method of determination of the thickness of thin metal films, used in the Kretschmann system, has been suggested. The hysteresis loops in the outgoing intensity versus input intensity curves were obtained experimentally when the light field increases and decreases consecutively.     

Incident-energy dependence of crystalline structures of ion beam deposited Au thin films

The energy dependence of crystalline structures in Au thin-film deposition processes was investigated with the use of a low-energy mass-selected ion beam system. Au films deposited on Si(100) untreated wafer surfaces by the beam system at different ion energies in the range of 20–200?eV were analyzed by atomic force microscopy (AFM), X-ray diffraction (XRD) and in-situ reflection high-energy electron diffraction (RHEED). The XRD results show that the kinetic energy provided by ion bombardment can facilitate crystal growth with specific orientations such as (100) or (110), the surfaces of which have relatively high surface energies. Our observations also suggest that each crystalline orientation appears only in a specific energy range of ion bombardment. These results indicate that Au crystalline orientations may be controlled by the ion irradiation energy during deposition processes.     

Photostimulated luminescence properties of BaFBr:Eu under ion irradiation

The photostimulated luminescence (PSL) properties of the phosphor BaFBr:Eu after ion beam irradiation was analyzed; in particular, the PSL intensity dependent on ion fluence. The PSL intensity increased linearly with the ion fluence up to 10¹² ions/cm², and subsequently decreased gradually. The ion fluence dependence was observed to be similar among samples containing different F centers or different Eu concentrations. The fluence dependence was quantitatively analyzed based on a trapping model, in which competition between the trapping processes to storage centers and radiation defects is assumed; the model explained the experimental data quantitatively. The results indicate that radiation defects influence the PSL properties via the trapping of photostimulated electrons.     

Dynamical diffraction of X-rays in ADP single crystal under influence of temperature gradient

The dependence of the integrated intensity of X-ray beams diffracted from a single crystal of ammonium dihydrogen phosphate (ADP) in the Laue geometry on the applied temperature gradient has been investigated. It is found that the integrated intensity of the X-ray beam reflected from a single crystal depends almost linearly on the magnitude of the temperature gradient, applied perpendicular to the reflecting atomic planes, up to saturation. For small values of the temperature gradient, in case of antiparallel vectors of diffraction and temperature gradient, integrated intensity of the reflected X-rays is initially reduced by about 10% and then increases monotonically with increasing value of the temperature gradient. Based on the theoretical analysis, an explanation of the observed phenomena is given.     

Three-dimensional resonant coherent excitation of nonchanneling ions in a crystal

We have observed resonant coherent excitation (RCE) of H-like Ar(17+) ions traveling through a 1 microm-thick Si crystal at an energy of 391 MeV/u in the nonchanneling condition. A three-dimensional periodic array of atomic planes induces RCE of the nonchanneling ions. The high energy heavy ions together with the thin crystal allow us to observe this new RCE through the measurements of the charge-state distribution of the emerging ions. The observed resonances are much narrower than those of planar-channeling ions due to the absence of the large Stark shift caused by the planar potential.     

Beam focusing upon the reflection from crystals and multilayer periodic structures with variable period

The experimental spectral dependence of the intensity of the second harmonic (SH) generated in microcavities based on porous silicon photonic crystal demonstrates resonant intensity enhancement (by a factor of ～2×10²) in the vicinity of the cavity mode and at the edges of the photonic band gap. The enhancement is due to the combined effect of pump radiation localization inside the microcavity, multiple SH interference in the photonic crystal, and two-photon resonance of the porous silicon quadratic susceptibility at the SH frequency.     

Theoretical study of the Smith-Purcell effect involving photonic crystals

The Smith-Purcell radiation spectrum is calculated for the trajectory of a running charge parallel to the surface of a photonic crystal of dielectric spheres. Analysis is given for the dependence of the spectrum on the velocity of the running charge, the distance of the trajectory from the photonic crystal, and on the light absorption of the photonic crystal. It is shown that all the characteristic features of the radiation spectrum are satisfactorily explained by treating a direct light emitted by the charge as an incident light on the photonic crystal.     

Structural,thermal, and optical properties of Er3+/Yb3+ co-doped oxyhalide tellurite glasses,glass-ceramics and ceramics

Glass-ceramics and ceramics containing nano-crystals of different phases doped with Er³⁺/Yb³⁺ ions have been successfully prepared by heat treatment of the precursor oxyhalide glasses synthesized by the melt-quench method. X-ray diffraction patterns and transmission electron microscopy (TEM) images verify the precipitation of nano-crystals. Emission of Er³⁺ enhances several times when Yb³⁺ ion is added with the matrix. The Stark splitting and the intensity of different emission bands increase to a great extent when we approach to ceramics from glasses via glass-ceramics. The intensity of the blue and green emission bands increases much faster than the red and NIR emission bands. Intense upconversion emission observed by the naked eye has been quantified in terms of standard chromaticity diagram (CIE). Power dependence study shows that the upconversion of NIR radiation to visible radiation takes place mainly via photon avalanche (PA) process.