Excitation of multiple wakefields by short laser pulses in quantum plasmas

We present a theoretical investigation of the excitation of multiple electrostatic wakefields by the ponderomotive force of a short electromagnetic pulse propagating through a dense plasma. It is found that the inclusion of the quantum statistical pressure and quantum electron tunneling effects can qualitatively change the classical behavior of the wakefield. In addition to the well-known plasma oscillation wakefield, with a wavelength of the order of the electron skin depth (λe=c/ωpe, which in a dense plasma is of the order of several nanometers, where c is the speed of light in vacuum and ωpe is the electron plasma frequency), wakefields in dense plasmas with a shorter wavelength (in comparison with λe) are also excited. The wakefields can trap electrons and accelerate them to extremely high energies over nanoscales.     

Ponderomotive acceleration of electrons by an ultrashort laser pulse

By using the corrected solutions for an ultrashort laser pulse, we study the laser-driven electron violent acceleration in vacuum. Our simulations demonstrate that an ultrashort laser pulse with an intensity a₀≡eE₀/m_eωc=3 can accelerate electrons to an energy more than 0.5 GeV. The scaling laws for the net energy gain in different pulse length and laser radius at focus are also studied. Its acceleration mechanism is found to be ponderomotive acceleration.     

Laser-driven electron beam and radiation sources for basic,medical and industrial sciences

To date active research on laser-driven plasma-based accelerators have achieved great progress on production of high-energy, high-quality electron and photon beams in a compact scale. Such laser plasma accelerators have been envisaged bringing a wide range of applications in basic, medical and industrial sciences. Here inheriting the groundbreaker’s review article on “Laser Acceleration and its future” [Toshiki Tajima, (2010)],¹⁾ we would like to review recent progress of producing such electron beams due to relativistic laser-plasma interactions followed by laser wakefield acceleration and lead to the scaling formulas that are useful to design laser plasma accelerators with controllability of beam energy and charge. Lastly specific examples of such laser-driven electron/photon beam sources are illustrated.     

Spin-0 and spin-1/2 particles in a constant scalar-curvature background

We study the Klein-Gordon and Dirac equations in the presence of a background metric ds²=−dt²+dx²+e^−2gx(dy²+dz²) in a semi-infinite lab (x>0). This metric has a constant scalar-curvature R=6g² and is produced by a perfect fluid with equation of state p=−ρ/3. The eigenfunctions of spin-0 and spin-1/2 particles are obtained exactly, and the quantized energy eigenvalues are compared. It is shown that both of these particles must have nonzero transverse momentum in this background. We show that there is a minimum energy E²_min=m²c⁴+g²c²?² for bosons (E_KG>E_min), while the fermions have no specific ground state (E_Dirac>mc²).     

Numerical studies on wakefield excited by Gaussian-like microwave pulse in a plasma filled waveguide

Based on a differential equation derived analytically in terms of wakefield potential ?_MW in a plasma filled rectangular waveguide, we investigate the wakefield (E_MW) generated with the help of Gaussian-like microwave pulse under the effect of microwave frequency (f), pulse duration (τ), waveguide width (b), equilibrium plasma density (n₀) and microwave intensity (I). The study conducted for three cases of τ > 1/f_p, τ = 1/f_p and τ < 1/f_p, where f_p is the plasma frequency, reveals that the amplitude of the wakefield is increased for the large pulse duration and higher microwave intensity but is decreased with the waveguide width and microwave frequency for all these cases. The wakefield shows stronger dependence on the microwave frequency when the microwave with larger intensity is used. The wakefield decreases at a faster rate with the waveguide width for the case of τ > 1/f_p.     

Magnetostriction, Curie temperature and microstructure of Tb0.29(Dy1−xPrx)0.71Fe1.97 oriented alloys

The Tb_0.29(Dy_1−xPr_x)_0.71Fe_1.97 (x=0, 0.1, 0.2 and 0.3) alloys were prepared by directional solidification method. The orientation, magnetostriction λ, Curie temperature T_c and microstructure of alloys were characterized by XRD, standard resistant strain gauge technique, VSM and SEM-EDS. The results reveal that the alloys have a preferred orientation of 〈1 1 0〉 and 〈1 1 3〉 direction when x>0. With the increase in Pr content, the T_c of alloys decreases gradually and the non-cubic phase appears, resulting in the decline of λ dramatically, from 1935.2×10⁻⁶ for x=0 to 695.9×10⁻⁶ for x=0.3 at a compressive stress of 6 MPa and a magnetic field of H=240 kA m⁻¹.     

Nuclear hyperfine structure in the XΣ state of ZrC

Electronic band systems of zirconium monocarbide, ZrC, in the 16 000-19 000 cm⁻¹ region have been observed following the reaction of laser-ablated Zr atoms with methane under supersonic free-jet conditions. Rotational analyses of high-resolution spectra have shown that the ground state of ZrC is a ³Σ state, with r₀=1.8066 Å and an unexpectedly small spin-spin parameter, λ=0.5139 cm⁻¹. The spectra are dense because of the five naturally occurring isotopes of Zr. Four of these, with mass numbers 90, 92, 94, and 96, have I=0, but the fifth, ⁹¹Zr, present in 11.22% abundance, has I=5/2. Lines of ⁹¹ZrC can be assigned in some of the strongest bands, and are found to display sizeable hyperfine splittings, with widths of up to 0.2 cm⁻¹. Analysis shows that the largest hyperfine effects are in the ground state, where b=−0.03133±0.00015 cm⁻¹ and c=−0.00123±0.00037 cm⁻¹ (3σ error limits). The large Fermi contact parameter, b, indicates that an unpaired Zr 5sσ electron is present, which, taken together with the small value of λ, means that the ground state must be a ³Σ⁺ state, from the electron configuration (Zr 5sσ)¹ (C 2pσ)¹. Internal hyperfine perturbations occur between the F₁ and F₃ electron spin components of the ground state in the range N=2-4, producing extra lines in some of the branches; the perturbations are of the type ΔN=0, ΔJ=±2, and are a second-order effect arising because the F₁ (J=N+1) and F₃ (J=N−1) spin components both interact with the F₂ (J=N) component through ΔN=0, ΔJ=±1 matrix elements of the Fermi contact operator. Second-order perturbations of this type can only occur in states that are very close to case (b) coupling.     

三角激光脉冲尾波加速粒子模拟

电子俘获是激光尾波场加速电子的主要机理，增大电子的初速度可以使更多的电子被尾波场俘获.提出三角脉冲激发尾波加速电子的方案，三角脉冲平缓上升沿激发受激Raman散射，用以初步加速电子，三角脉冲陡峭下降沿激发尾波场，将更多的电子加速到接近光速.2D3V粒子模拟结果证实了这一点.同时表明：脉冲长度为几个等离子体波长的超强激光在稀薄等离子体中传播时，还激发侧向Raman散射.在侧向受激Raman散射中，静电波增长最快的波矢模式为k_p=(2ω_p/ω₀ 关键词： 有质动力 电子俘获 前向受激Raman散射 侧向受激Raman散射     

Superluminal energy transmission in the Goos-Hanchen shift of total reflection

The dispersion relation ω² = β²c² − τ²c² of surface electromagnetic waves is corresponding to that E² = p²c² − m₀²c⁴ of a tachyon where the coefficient of proportionality is the squared Planck constant ?². Then we prove the energy flow velocity of the Goos-Hanchen shift in vacuum is cn sin θ_i > c as well according to electrodynamics. These two different ways lead to a same conclusion that energy transport in the Goos-Hanchen effect of total reflection is faster than light.     

Plasma guiding and wakefield generation for second-generationexperiments

A design study has been carried out for a second-generation experiment on laser guiding and wakefield excitation in a channel. From simple scaling laws for the wakefield amplitude, dephasing length, the relativistic group velocity factor γ_g, and energy gain with and without guiding, we find that the parameter regime for a compact single stage GeV accelerator favors laser systems producing short pulses (10 fs⩽τ⩽100 fs), each containing an energy on the order of 100 mJ to a few J's. Taking the dephasing length as the maximum acceleration distance, plasma channels with lengths of 1-10 cm and densities of 10¹⁷-10¹⁹ cm^-3 need to be produced; whereas the design study has been primarily concerned with diffraction and channel guiding, dephasing and depletion limits, and linear wakefield theory, aspects of the effect of the plasma wave on the evolution of the laser pulse are discussed. We find that transverse and longitudinal pulse distortions could indeed affect the generated plasma wave phase velocity and amplitude, and hence may limit the achievable energy gains over the one-dimensional (1-D) linear estimates. Some issues for experiments on prototype small accelerators (100 MeV-1 GeV, cm scale) are also discussed     

Absorption and fluorescence studies of Sm ions in lead containing sodium fluoroborate glasses

Lead containing calcium zinc sodium fluoroborate glasses (LCZSFB) with molar composition of 20PbO+5CaO+5ZnO+10NaF+(60−x) B₂O₃+x Sm₂O₃, (x=0.1, 0.25, 0.5, 1.0 and 2.0 mol%) were prepared and investigated by the XRD, FTIR, optical absorption, photoluminescence and decay curve analysis. Judd-Ofelt theory was applied to the experimental oscillator strengths to evaluate the phenomenological J-O intensity parameters Ω_λ (λ=2, 4 and 6). Using the J-O intensity parameters as well as from the emission and decay measurements, various radiative parameters such as transition probabilities (A_R), radiative lifetimes (τ_R), measured lifetimes (τ_m), calculated branching ratios (β_R), measured branching ratios (β_m), effective bandwidth (Δλ_eff) and stimulated emission cross sections σ(λ_p) have been calculated for the excited ⁴G_5/2 luminescent level. The nature of decay curves of ⁴G_5/2 level for different Sm³⁺ ion concentrations in all LCZSFB glasses has been analyzed and the lifetimes are noticed to decrease with increase of concentration. The concentration quenching has been attributed to the energy transfer through the cross-relaxation between Sm³⁺ ions. Based on these results, the utility of Sm³⁺ ions doped lead containing fluoroborate glasses as laser active materials in the visible region is discussed.     

Quantitative relation between the thermionic contrast of metal surfaces and their degree of monocrystallization

For better understanding the peculiarities of work function, a simple model is devised to calculate the effective work functions (?⁺ and ?^e) for positive-ionic and electronic emissions from polycrystalline surfaces, which have a work function range from the maximum (?_max) to the minimum (?_min). Analysis of the theoretical results thus obtained and also of experimental data published to date enables us to find the quantitative relation between the thermionic contrast (Δ?^* ≡ ?⁺ − ?^e) and the degree of monocrystallization (δ_m), thereby yielding the three formulae of (1) Δ?^* = c for 0 < δ_m ? 1/2 (polycrystal), (2) Δ?^* = 4 cδ_m (1 − δ_m) for l/2 ? δ_m ? 1 (polycrystal), and (3) Δ?^* = 0 for δ_m = 1 (monocrystal). For a given surface consisting of a number of patchy faces (i), δ_m corresponds to the largest among its fractional surface areas (F_i) having different values of local work function (?_i). In a typical case of tungsten, the constant of c is evaluated theoretically to be 0.53 ± 0.09 eV, which well agrees with 0.59 ± 0.06 eV determined experimentally by many workers and also which satisfies the essential condition of Δ?^* ≦ c < ?_max − ?_min ≈ 0.8-1.0 eV. Our theoretical model is quite simple, but it is very useful for (1) evaluating both ?⁺ and ?^e with an uncertainty of less than ±0.1 eV, (2) finding the quantitative relation between Δ?^* and δ_m for actual surfaces of both poly- and monocrystals, and also (3) getting a substantial clue as to the problem how the effective work functions are governed by the surface characteristics of both F_i and ?_i.     

Direct synthesis of mesoporous carbon from the carbonization of hydroxypropyl-β-cyclodextrin/silica composite and its catalytic performance

A simple and efficient route is reported for the synthesis of mesoporous carbon materials by directly carbonizing hydroxypropyl-β-cyclodextrin-silica composites. The resulting carbon materials, with uniform wormlike mesoporous structure and certain degree graphitic phase characteristics in porous wall, possess narrow pore size distribution, high surface area (>1000 m² g⁻¹) and pore volume (>1.2 cm³ g⁻¹). It is worth mentioning that the carbon materials have high catalytic activity for the reduction of p-nitrotoluene using hydrazine hydrate as the reducing agent; moreover, the catalytic activity is not reduced notably after being reused for six times.     

Rényi entropy and quantum phase transition in the Dicke model

The Rényi entropies of the Dicke model are presented. This quantum-optical model describes a single-mode bosonic field interacting with an ensemble of N two-level atoms. There is a quantum phase transition in the N→∞ limit. It is shown that there is an abrupt change in the Rényi entropy of order β at the transition point. Around the critical value of the coupling strength λc the Rényi entropy is proportional to the logarithm of the characteristic length and diverges as ln|λc−λ| for any order β. The pseudocapacity defined here in analogy with the heat capacity exhibits the phase transition. The critical exponent for the Dicke model is found to be 1 for any value of the parameter β.     

Scaling in pπ → pX and an estimate of the triple-Pomeranchukon coupling

We show that the CERN-IHEP data on pπ⁻ → pX⁻ at 25 and 40 GeV/c exhibit scaling in s′/s. We give an estimate of the triple-Pomeranchukon coupling and discuss the possibility of its measurement at NAL.     

聚丁二烯中的等待时间效应

测量了高聚物材料聚丁二烯的比热,发现在温度T_g=178K出现玻璃转变且转变点附近的比热与降温过程有关。在降温过程中,若控制样品在某一温度T_wg等待时间t_w,则升温比热测量表明,T_g处的比热跃变△c_p存在明显的等待时间效应,即△c_p随t_w的增大而增大。在T_w=169K条件下,△c_p(t< 关键词：     

A Laser-Induced Fluorescence Study of the Visible Spectrum of Rhodium Monoxide

A first analysis of an electronic spectrum of RhO is presented. The molecular species has been produced in a jet-cooled molecular beam following reaction in a laser ablation plasma. Laser excitation spectra have been recorded between 600 and 640 nm at 200 MHz resolution. Two transitions have been identified of ²Π_r(a)-X⁴Σ⁻(b) type and six subbands have been rotationally analyzed, four being (0,0) components. Molecular parameters for the X⁴Σ ⁻ state are B₀=0.41320 cm⁻¹, λ₀=−0.5733 cm⁻¹, γ₀=−0.10276 cm⁻¹, and r₀=0.1717 nm. An analysis of the hyperfine structure involving the ¹⁰³Rh nucleus has been made. It shows that the ground state of RhO conforms to Hund's coupling case b_βJ with b=− 0.0203 cm⁻¹. Hyperfine effects in the excited states are negligible.     

Numerical analysis of long wavelength infrared HgCdTe photodiodes

We present a detailed investigation of the performance limiting factors of long and very long wavelength infrared (LWIR and VLWIR) p on n Hg_1−xCd_xTe detectors through numerical simulations at 77 K incorporating all considerable generation-recombination (G-R) mechanisms including trap assisted tunneling (TAT), Shockley-Read-Hall (SRH), Auger and radiative processes. The results identify the relative strengths of the dark current generation mechanisms by numerically extracting the contribution of each G-R mechanism to the detector characteristics with various cut-off wavelengths (λ_c) and practically achievable material parameters.The results show that the dominant sensitivity degrading trap level depends on the detector cut-off wavelength being ∼0.7E_g for LWIR HgCdTe sensors (λ_c = ∼10 μm) instead of 0.5E_g which is generally believed to be the most efficient R-G level. TAT related 1/f noise dominates the sensor noise even under small reverse bias voltages at a trap density as low as 1 × 10¹⁴ cm⁻³ for sensors with λ_c > 11 μm. Considering the fact that trap densities below this level are rarely reported for HgCdTe material, exceptionally trap-free material is required to achieve desirable imaging performance with these sensors. Simulation results show that Auger mechanism has twofold effect on the sensitivity of the sensor by increasing the dark current and decreasing the photo current of the detector.     

Temperature dependence of the energy separation between Γ and L minima in n-type GaSb

Energy separation ΔE_c between Λ and L minima of GaSb conduction band is deduced from temperature dependence of tunneling current in p−n junctions. ΔE_c is found to inceasing vx. temperature with a coefficient d(ΔE_c/dT) of about - 2.10^-4eV/dgK.     

Theoretical study of local crystal structure in KZnF3:Fe system

An analysis of the relationship between the EPR trigonal-field parameters and the local crystal structure of KZnF₃:Fe³⁺system is presented by diagonalizing the complete energy matrices for a d⁵ configuration ion in a trigonal crystal field. We propose a two-layer-ligand model, in which the ligands consist of six nearest-neighbor F⁻ ions in the first layer and eight next nearest-neighbor K⁺ ions in the second layer. The calculation indicates that the local structure distortion of KZnF₃:Fe³⁺system is due to the displacement of a K⁺ ion along C₃ axis towards the Fe³⁺ ion, which leads to the shift of the F⁻ ions away from C₃ axis. By simulating the EPR low-symmetry parameters D and (a−F), the distorted angles between the Fe³⁺-F⁻ bonds and C₃ axis are determined, Δθ₁=2.58°, Δθ₂=−1.4° at room temperature (300 K) and Δθ₁=2.84°, Δθ₂=−1.4° at low temperature (77 K). Those results are in good agreement with the experimental findings Δθ₁=2.8±0.3°and Δθ₂=−1.1±0.3°.