利用离子激发发光研究低温条件下ZnO发光行为EI北大核心CSCD

离子激发发光(Ions beam induced luminescence,IBIL)可以实时原位分析不同温度、不同离子辐照条件下材料内部点缺陷的演变行为。本文利用2 MeV H^(+)研究了300,200,100 K温度下ZnO单晶内部点缺陷发光及其随注量的演变行为。实验中发现ZnO深能级发射和近带边发射,结合Voigt分峰与XPS实验结果,确定红光(1.75 eV)与V_(Zn)相关,橙红光(1.95 eV)来自Zn_(i)到O_(i)跃迁;对于与V_(O)相关的绿光(2.10 eV),其红移可能由于温度降低导致更多电子由导带释放到Zn_(i)。峰中心位于3.10 eV和3.20 eV近带边发射分别来自于Zn_(i)到价带的跃迁和激子复合,红移原因分别为Zn_(i)附近局域化能级和带隙收缩。利用单指数公式对发光强度进行拟合,获得的衰减速率常数(f)可以表征缺陷的辐射硬度,对比发现深能级发射峰在200 K时辐射硬度最大,而近带边发射峰在300 K时辐射硬度最大。     

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.     

Latent track creation in fused silica by 200 MeV silver beam

Studies of formation of latent tracks in swift heavy ion irradiated SiO₂ are presented. Fused silica (SiO₂) were irradiated with 200 MeV silver (Ag) ion beam at varying fluences. Radiation-induced effects were studied by ultraviolet(UV)/Visible optical absorption spectroscopy and transmission electron microscopy (TEM). UV/Visible absorption study indicated E′ centers and oxygen deficiency centers having characteristic absorption occurred at 5 eV. The density of these color centers calculated from the absorption peak intensity showed Poisson-type variation with irradiation fluence. The defects are thus entirely confined to the latent tracks created by swift heavy ions in SiO₂. The track radius estimated from optical absorption study was found to be 5.1 nm. Similar results were obtained from TEM studies of the irradiated samples.     

Excimer lasers and laser systems

The results of the experimental study of UV lasers and laser systems pumped by different methods are presented. Two lasers were pumped by electron beams from Marx generators. Three lasers were pumped by transverse discharge with UV preionization. An XeCl laser pumped by electric discharge using a generator with inductive energy storage and semiconducting opening switch is investigated. The highest laser radiation energies of 2000, 90, and 0.7 J have been obtained at 5=308, 249, and 222 nm, respectively. The amplification of the laser beam from the master oscillator under conditions of strong amplified spontaneous emission is considered. In particular, formation of the output from an amplifier in the wings of the XeCl laser band and in the case of a large-aperture XeCl amplifier are investigated. The output beam divergence in these experiments was measured to be ~10^-4 rad.     

紫外激光作用下环氧乙烷的TOF质谱研究

本文采用超声分子束技术,分别在308nm和355nm的紫外激光下,对环氧乙烷分子进行了多光子电离飞行时间(TOF)质谱研究.在308nm激光作用时,观测到C_2H_4O~+、C_2H_3O_+、CHO~+和CH_3~+等离子的信号;在355nm激光作用时,则没有观测到分子离子的信号.在两种激光作用下最强的信号都是CHO~+.但是两种激光下各碎片离子信号的光强指数有一定差别,表明在两种情形下,环氧乙烷分子经历了不同的电离解离过程.     

Time-resolved and integrated angular distributions of plume ions from silver at low and medium laser fluence

Laser impact on metals in the UV regime results in a significant number of ablated plume ions even at moderate fluence (0.7–2.4 J/cm²). The ablated particles are largely neutrals at the lowest fluence, but the fraction of ions increases strongly with fluence. The ion flow in different directions from a silver target irradiated by a laser beam at a wavelength of 355 nm in vacuum was measured with a hemispherical array of Langmuir probes. The time-of-flight spectra in all directions, as well as the total angular yield were determined. The angular distribution peaks strongly in forward direction with increasing fluence and can be well approximated by Anisimov’s model. Typically, the spectra of silver ions peak from 70 eV up to 145 eV in a direction close to the normal of the target surface with increasing fluence. With increasing observation angle, the time-of-flight spectra exhibit a peak at longer flight times, i.e., at a lower kinetic energy. At the highest fluence, the ionized fraction of the ablated particles in the plume increases up to 0.5.     

Modification of the amorphous carbon films by the ns-laser irradiation

The effect of a nanosecond laser irradiation of thin (60 and 145 nm) amorphous, diamond-like carbon films deposited on Si substrate by an ion beam deposition (IBD) from pure acetylene and acetylene/hydrogen (1:2) gas mixture was analyzed in this work. The films were irradiated with the infrared (IR) and ultraviolet (UV) radiation of the nanosecond Nd:YAG lasers working at the first (1.16 eV) and the third (3.48 eV) harmonics, using a multi-shot regime. The IR laser irradiation stimulated a minor increase in the fraction of sp² bonds, causing a slight decrease in the hardness of the films and initiated SiC formation. Irradiation with the UV laser caused the formation of carbides and increased hydrogenization of the Si substrate and the fraction of sp² sites. Spalliation and ablation were observed at a higher energy density and with a large number of laser pulses per spot.     

Surface modifications of PADC polymeric material by ion beam bombardment for high technology applications

Surface modification of Poly (allyl diglycol carbonate) (PADC) is induced by 150 keV Ag ions of different fluences. The pristine as well as bombarded samples were investigated by UV–Vis spectroscopy, Fourier transform-infrared analysis (FTIR) and micro-hardness tester. The variations of wettability and surface free energy were determined by the contact angle measurements. The obtained results showed that ion beam bombardment induced increase in the absorption spectra of the UV–Vis with increase of ion fluence as well. The direct and indirect optical band gap decreased from 4.2 to 3.6 eV for pristine sample to 3.2 and 2.5 eV for those bombarded with Ag ion beam at the highest fluence, respectively. Changes in chemical properties were observed by Fourier transform infrared spectroscopy. Increase in the wettability, surface free energy and work of adhesion with increase the ion fluence were observed. Ion bombardment inducing increasing in a micro-hardness surface due to the high carbon surface concentration and cross-linking effects in the polymeric chains. The bombarded PADC surfaces may find special applications to the field of the micro-electronic devices and printing process.     

Ion and X-ray techniques used for study of laser-produced plasmas

This review article describes apparatus for ion and X-ray diagnostics, which were used in experimental studies of laser-produced plasmas performed by the IPPLM's team in collaboration with other researchers at IPPLM and PALS Research Centre in Prague (the Czech Republic). The investigations of expanding laser-produced plasma properties in dependence on laser beam parameters were done by means of ion diagnostics devices: ion collectors (ICs), cylindrical ion energy analyzer (IEA) and the mass spectrograph of the Thomson type. At IPPLM, different types of detectors have been developed for measurement of X-ray emission. Properties of laser-produced beams of ions and X-ray radiation were analysed in the cooperative experiments performed with the use of a high-energy iodine laser PALS at the PALS Research Centre ASCR in the Czech Republic and the low-energy repetitive laser at IPPLM.     

紫外激光照射引起的硅酸铅玻璃结构的变化

采用紫外-可见吸收光谱和电子自旋共振谱(ESR)对硅酸铅玻璃薄膜和体材料受紫外激光照射前后的结构变化进行了研究。研究发现：266 nm的紫外激光照射硅酸铅玻璃体材料时,能使其Urbach能量增大,即玻璃结构的无序性增大。电子自旋共振谱研究表明,266 nm激光照射不会在硅酸铅玻璃中产生顺磁缺陷中心, 也不会对硅酸铅玻璃薄膜在235 nm附近的吸收峰产生影响,但用248 nm紫外激光照射则观察到了235 nm吸收峰的光漂白现象。     

Measurement of the KLL Dielectronic Recombination Resonances in He-like to C-like Kr Ions

The KLL dielectronic recombination processes of highly charged He-like to C-like Kr ions have been studied experimentally. The measurement was performed on the newly developed Shanghai electron beam ion trap （Shanghai-EBIT） facility. Characteristic x-rays from both dielectronic recombination and radiative recombination are detected as the electron beam energy is scanned through the resonances. The KLL resonant strengths obtained are 5.41×10^-19, 4.33×10^-19, 3.59×10^-19, 2.05×10^-19 and 0.98×10^-19 cm^2 eV for He-like to C-like Kr ions, respectively.     

Investigation of luminescence processes in YAG single crystals irradiated by 50 MeV electron beam

Absorption, emission and excitation spectra of 50 MeV electron beam irradiated and as-grown YAG single crystals were studied and compared in the 10–300 K temperature range using time-resolved luminescence spectroscopy under UV/VUV/XUV excitation by synchrotron radiation and cathodoluminescence. The emission spectra consist of intrinsic (excitonic) and defect related non-elementary bands in the VIS/UV range. It is shown that fast electrons create stable F and F⁺ color centers with characteristic emission and absorption bands in the visible/UV range. Induced absorption caused from these defects starts at 4.2 eV. Energy transfer from host to color centers is not an efficient process.     

Micro-Raman and ion channeling study of crystal damage in Si induced by focused Co ion beam implantation

The lattice damage of silicon produced by ion implantation at extremely high current density of 0.8 A/cm² (2.5᎒¹⁸ cm^-2 s^-1) was investigated. In a focused ion beam system, implantation was carried out with 70 keV Co ions, fluences of 1.2᎒¹⁶ cm^-2 and 6.7᎒¹⁵ cm^-2 into Si (111) at room temperature and elevated temperatures between 355 °C and 400 °C. Radiation damage measurements were performed by Rutherford backscattering/channeling spectroscopy and micro-Raman analysis. The radiation damage was studied as a function of pixel dwell-time and implantation temperature. The critical temperature for amorphization increases with current density. Although the fluence of the focused ion implantation was constant, crystalline layers were obtained for short and amorphous layers for long pixel dwell-times. The critical dwell-time of crystalline/amorphous transition increases with implantation temperature. From the results a typical time for defect annealing of 10^-5 s at 400 °C and an activation energy of (2.5ǂ.6) eV were deduced.     

Nanocrystalline growth and diagnostics of TiC and TiB2 hard coatings by pulsed laser deposition

Nanocrystalline coatings of TiC and TiB₂ were grown by pulsed laser deposition on Si(100) and on X155 steel at low substrate temperatures ranging from 40 °C to 650 °C. A pulsed KrF excimer laser was used with the deposition chamber at a base pressure of 10^-6 mbar. The morphology and structure of the films, studied with SEM, XRD, and TEM, showed that nanocrystalline films with a fine morphology of TiC and TiB₂ were deposited with a grain size of 10 nm-70 nm at all substrate temperatures. The growth of the polycrystalline coatings possessed a columnar morphology with a 𘜄¢ preferred orientation. The hardness of the coatings was determined to be 40 GPa and the elastic modulus, 240 GPa. The composition and the kinetics of the plume produced during the pulsed laser deposition of TiC and TiB₂ was studied under film growth conditions. The mass analysis of ions of the ejected material was performed by time-of-flight mass spectroscopy (TOF-MS) and showed the presence of Ti⁺ and C⁺ during TiC ablation and B⁺, B₂⁺, and Ti⁺ during TiB₂ ablation. The kinetic energies (KE) of the ions depended on the laser fluence which was between 0.5 eV and 340 eV. The kinetic energy and the evolution of the plasma was studied with a streak camera. The velocity of the plasma was of the order of 10⁶ cm/sec and was linearly dependent on the energy fluence of the laser. The emission spectroscopy of the plasma plume confirmed the atomic neutral and single excited species of Ti. These results show that coating growth basically occurs by the recombination of the ionic species at the surface of the substrate.     

Laser ablation of carbon at the threshold of plasma formation

The ionization of laser-ablated vapours with lasers producing ns duration pulses at various wavelengths has been studied in order to understand the mechanisms of the vapour-plasma transition. It has been established that there are several regimes characterizing the laser-target interaction which depend on laser intensity, wavelength, and pulse duration. The range of laser intensities for optimal laser evaporation is determined by the condition of transparent vapours. The intensity range is upper-limited by the opaque plasma formation due to vapour optical breakdown. Results are given for laser evaporation of graphite with Nd:YAG laser (1.064 7m), KrF laser (248 nm) and ArF laser (193 nm). For the UV laser wavelength the regime of skin-effect interaction was proposed as the mechanism of ion acceleration, and the range of validity of the skin-effect mode was established. With UV lasers the interaction has a bimodal nature: the interaction may proceed initially in the skin effect regime, resulting in a few high-energy ions, until hydrodynamic expansion begins at a later stage. The skin-effect interaction at the initial stage of the UV laser pulse gives the first, to our knowledge, explanation for the acceleration of ions up to ~100 eV at low laser intensities of 10⁸-10⁹ W/cm² and ns-range pulse duration.     

Ge：SiO2的光敏缺陷的研究

研究了Ｇｅ；ＳｉＯ２光敏缺陷的特性，分别在４８８ｎｍＡｒ离子激光与１９３ｎｍＡｒ准分子激光作用下，由紫外吸收带，激光荧光的测量实验及电子自旋共振实验，发现光纤中５．１ｅＶ锗缺陷吸收带实验上是由５．０６ｅＶ可光致漂白带与５．１７ｅＶ不可漂白带组成；２９５ｎｍ的激发荧光与５．０６ｅＶ的缺氧锗缺陷对应，随５．０６ｅＶ缺陷吸收带的漂白而衰减；     

Laser Accelerated, High Quality Ion Beams

Intense beams of protons and heavy ions have been observed in ultra-intense laser-solid interaction experiments. Thereby, a considerable fraction of the laser energy is transferred to collimated beams of energetic ions (e.g. up to 50 MeV protons; 100 MeV fluorine), which makes these beams highly interesting for various applications. Experimental results indicate very short pulse duration and an excellent beam quality, leading to beam intensities in the TW range. To characterize the beam quality and its dependence on laser parameters and target conditions, we performed experiments at several high-power laser systems. We found a strong dependence on the target rear surface conditions allowing to tailor the ion beam by an appropriate target design. We also succeeded in the generation of heavy ion beams by suppressing the proton amount at the target surface. We will present recent experimental results demonstrating a transverse beam emittance far superior to accelerator-based ion beams. Finally, we will discuss the prospect of laser-accelerated ion beams as new diagnostics in laser-solid interaction experiements. Special fields of interest are proton radiography, electric field imaging, and relativistic electron transport inside the target.     

Luminescence properties of silver zinc phosphate glasses following different irradiations

We report on exposing a photosensitive zinc phosphate glass containing silver to different radiation (electron, gamma, optical). Laser irradiations using nanosecond ultraviolet (UV) and femtosecond infrared (IR) laser are compared with gamma and electron exposure. All irradiated glasses exhibit absorption maxima around 320 nm and 380 nm and emission in the visible spectral range. Following exposure, silver clusters are formed. The optical response of such species is investigated using absorption and fluorescence spectroscopic techniques. The mechanism of formation of these clusters is discussed.     

Nonlinearity and time-resolved studies of ion emission in ultrafast laser ablation of graphite

We have investigated the laser fluence dependence of the ion emission process in ultrafast laser ablation of graphite using a time-of-flight technique. Two regimes of ion emission have been identified: (1) a highly nonlinear laser absorption process accompanied by generation of a transient electrical field on the surface and collisionless emission of ions due to electrostatic repulsion; (2) a saturation regime for laser power absorption characterised by nearly equal kinetic energy of ejected carbon clusters. We also show the effect of the surface temperature on the emitted clusters’ stability and the influence of nonlinearity on the intensity autocorrelation traces.     

Mass spectrometric detection of molecular ions formed by irradiation of condensed methanol with a CO2 laser

IR laser-induced ionization is investigated in condensed methanol (77 K) using a TEA CO₂ laser for resonant vibrational excitation and a quadrupole mass spectrometer to analyse the ion spectra produced by laser irradiation. Ions are already detected at laser fluences below 1 J/cm², far below dielectric breakdown. The fluence dependence of the ion yield is measured for two groups of ions and the total number of ions. A mechanism is proposed for the photochemical production of protonated molecules. The protonated monomer is the species with the highest abundance; however, protonated dimers and other quasimolecular ions and fragment ions are also found.