Formation of Luminescence Centers in Oxygen-Deficient Cerium Oxide Nanocrystals

In this work the peculiarities of oxygen vacancies formation in cerium oxide nanoparticles for different external influences have been investigated by spectroscopic methods. The features of oxygen vacancies and therefore non-stoichiometric cerium oxide formation in CeO2 nanocrystals depending on the atmosphere of high temperature treatment were investigated. Stimulation of oxygen vacancies formation in reducing and neutral atmospheres was revealed. Occurrence of two different luminescence centers (viz. the charge-transfer complexes formed by Ce4+ and O2- ions, and Ce3+ ions stabilized by vacancies) after cerium oxide nanoparticles annealing in a neutral atmosphere has been observed. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3544

High‐Intensity Laser Triggered Proton Acceleration from Ultrathin Foils

The recently developed PIC code MANDOR features arbitrary target design including 3D preplasma and the 6‐component laser fields of a tightly focused laser beam. The 3D simulations have been performed to model recent HERCULES experiments on proton acceleration, where protons with energy greater than 20 MeV were produced using just 1.5 J laser pulses focused to intensity of 2 × 10 21 W/cm 2 . By adapting the 3D target geometry relating to ps‐prepulse effect, reasonable agreement with experimental data for the proton energy spectrum has been achieved. The effect of the 3D preplasma shape on efficiency of proton acceleration is discussed. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/96347/1/161_ftp.pd

Swarm of ultra-high intensity attosecond pulses from laser-plasma interaction

We report on the realistic scheme of intense X-rays and γ-radiation generation in a laser interaction with thin foils. It is based on the relativistic mirror concept, i.e., a flying thin plasma slab interacts with a counterpropagating laser pulse, reflecting part of it in the form of an intense ultra-short electromagnetic pulse having an up-shifted frequency. A series of relativistic mirrors is generated in the interaction of the intense laser with a thin foil target as the pulse tears off and accelerates thin electron layers. A counterpropagating pulse is reflected by these flying layers in the form of a swarm of ultra-short pulses resulting in a significant energy gain of the reflected radiation due to the momentum transfer from flying layers.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85400/1/jpconf10_244_022029.pd

Laser-triggered ion acceleration and table top isotope production

We have observed deuterons accelerated to energies of about 2 MeV in the interaction of relativistically intense 10 TW, 400 fs laser pulse with a thin layer of deuterated polystyrene deposited on Mylar film. These high-energy deuterons were directed to the boron sample, where they produced ∼ 105∼105 atoms of positron active isotope 11C11C from the reaction 10B(d,n)11C.10B(d,n)11C. The activation results suggest that deuterons were accelerated from the front surface of the target. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70713/2/APPLAB-78-5-595-1.pd

Suppression of impurity ions optical transitions dephasing in nanocrystals

Abnormally narrow spectral lines have been observed in the luminescence spectra of Y₂SiO₅Pr³⁺ and YVO₄:Eu³⁺ nanocrystals at the room temperature. This fact was interpreted as the result of optical transitions dephasing processes suppression in the nanocrystals. The general cause of the observed effect is the weakening of phonon scattering on the impurity centre as a result of the quantum size effect in nanocrystal phonon subsystem. At first the dependence of spectral line width on the nanocrystal size has been shown. Unnecessary of the deep cooling for narrow optical resonances obtaining makes these nanocrystals a potential candidate for the wide set of applications in the optical memory and quantum computing devices.На спектрах люмінесценції нанокристалів Y₂SiO₅Pr³⁺ та YVO₄:Eu³⁺ за кімнатної температури спостерігалася наявність аномально вузьких спектральних ліній. Це було інтерпретовано як результат заглушення процесів дефазування оптичних переходів у нанокристалах. Причиною зазначеного ефекту є ослаблення розсіювання фононів на домішковому центрі внаслідок впливу квантово-розмірного ефекту на підсистему фононів у нанокристалі. Уперше отримано залежність ширини спектральних ліній від розміру нанокристала. Відсутність потреби глибокого заморожування для отримання вузьких оптичних резонансів відкриває можливості використання таких нанокристалів для створення пристроїв оптичної памяті та квантових компютерів.На спектрах люминесценции нанокристаллов Y₂SiO₅Pr³⁺ и YVO₄:Eu³⁺ при комнатной температуре наблюдалось наличие аномально узких спектральных линий. Это было интерпретировано как результат подавления процессов дефазировки оптических переходов в нанокристаллах. Причиной наблюдаемого эффекта является ослабление рассеяния фононов на примесном центре в результате влияния квантово-размерного эффекта на подсистему фононов в нанокристалле. Впервые получена зависимость ширины спектральных линий от размера нанокристалла. Отсутствие необходимости глубокого замораживания для получения узких оптических резонансов открывает широкие возможности применения данных нанокристаллов для создания устройств оптической памяти и квантовых компьютеров

Generation of GeV protons from 1 PW laser interaction with near critical density targets

The propagation of ultra intense laser pulses through matter is connected with the generation of strong moving magnetic fields in the propagation channel as well as the formation of a thin ion filament along the axis of the channel. Upon exiting the plasma the magnetic field displaces the electrons at the back of the target, generating a quasistatic electric field that accelerates and collimates ions from the filament. Two-dimensional Particle-in-Cell simulations show that a 1 PW laser pulse tightly focused on a near-critical density target is able to accelerate protons up to an energy of 1.3 GeV. Scaling laws and optimal conditions for proton acceleration are established considering the energy depletion of the laser pulse.Comment: 26 pages, 8 figure

Study of Energetic Ion Generation from High-Intensity-Laser Dense-Plasma Interactions

We report on the characteristics of an ultrafast-laser driven proton beam from thinfilm targets. The difference in proton beam profiles, beam energies, and laser induced back ablation plumes between a dielectric (Mylar) and a conductor (aluminum) are discussed. Evidence for front-side acceleration and a method for beam manipulation are also presented

Nonlinear relativistic optics in the single cycle, single wavelength regime and kilohertz repetition rate

Pulses of few optical cycles, focused on one wavelength with relativistic intensities can be produced at a kilohertz repetition rate. By properly choosing the plasma and laser parameters, relativistic nonlinear effects, such as channeling and electron and ion acceleration to tens of megaelectronvolts are demonstrated. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87926/2/138_1.pd

Control of proton energy in ultra-high intensity laser-matter interaction

Recent breakthroughs in short pulse laser technology resulted in (i) generation of ultra-high intensity (2×1022 W/cm2) and (ii) ultra-high contrast (10−11) short pulses at the Hercules facility of the University of Michigan, which has created the possibility of exploring a new regime of ion acceleration – the regime of Directed Coulomb Explosion (DCE). In this regime of sufficiently high laser intensities and target thicknesses approaching the relativistic plasma skin depth it is possible to expel electrons from the target focal volume by the laser's ponderomotive force allowing for direct laser ion acceleration combined with a Coulomb explosion. That results in greater than 100 MeV protons with a quasi-monoenergetic energy spectrum. The utilization of beam shaping, namely, the use of flat-top beams, leads to more efficient proton acceleration due to the increase of the longitudinal field. According to the results of 2D PIC simulations a 500 TW laser pulse with a super-Gaussian beam profile interacting with 0.1 micron aluminium-hydrogen foil is able to produce monoenergetic protons with the energy up to 240 MeV.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85403/1/jpconf10_244_042025.pd

Energetic electron and ion generation from interactions of intense laser pulses with laser machined conical targets

The generation of energetic electron and proton beams was studied from the interaction of high intensity laser pulses with pre-drilled conical targets. These conical targets are laser machined onto flat targets using 7–180 µJ pulses whose axis of propagation is identical to that of the main high intensity pulse. This method significantly relaxes requirements for alignment of conical targets in systematic experimental investigations and also reduces the cost of target fabrication. These experiments showed that conical targets increase the electron beam charge by up to 44 ± 18% compared with flat targets. We also found greater electron beam divergence for conical targets than for flat targets, which was due to escaping electrons from the surface of the cone wall into the surrounding solid target region. In addition, the experiments showed similar maximum proton energies for both targets since the larger electron beam divergence balances the increase in electron beam charge for conical targets. 2D particle in cell simulations were consistent with the experimental results. Simulations for conical target without preplasma showed higher energy gain for heavy ions due to 'directed coulomb explosion'. This may be useful for medical applications or for ion beam fast ignition fusion.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85411/1/nf10_5_055006.pd