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We shall study in this paper the convergence rates of the Tikhonov regularized solutions for the recovery of the radiativities in elliptic and parabolic systems in general dimensional spaces. The conditional stability estimates are first derived. Due to the difficulty of the verification of the existing source conditions or nonlinearity conditions of the inverse radiativity problems in high dimensional spaces, some new variational source conditions are proposed. The conditions are rigorously verified in general dimensional spaces under the conditional stability estimates. We will also derive the reasonable convergence rates under the new source conditions, and the results reveal the explicit relation between the regularity of the radiativities and the convergence rates. [ABSTRACT FROM AUTHOR]

In this work, a 90-nm critical dimension (CD) technological process in an ArF laser lithography system is simulated, and the swing curves of the CD linewidth changing with photoresist thickness are obtained in the absence and presence of bottom antireflection coating (BARC). By analysing the simulation result, it can be found that in the absence of BARC the CD swing curve effect is much bigger than that in the presence of BARC. So, the BARC should be needed for the 90-nm CD manufacture. The optimum resist thickness for 90-nm CD in the presence of BARC is obtained, and the optimizing process in this work can be used for reference in practice. [ABSTRACT FROM AUTHOR]

A four-state model considering the relative velocity distribution function for calculating the cross section of laserinduced collisional energy transfer in a Sr-Li system is presented and profiles of laser-induced collision cross section are obtained. The resulting spectra obtained from different intermediate states are strongly asymmetrical in an opposite asymmetry. Both of the two intermediate states have contributions to the final state, and none of the intermediate states should be neglected. The peak of the laser-induced collisional energy transfer (LICET) profile shifts toward the red and the FWHM becomes narrower obviously with laser field intensity increasing. A cross section of 1:2×10-12 cm2 at a laser field intensity of 2:17×107 V/m is obtained, which indicates that this collision process can be an effective way to transfer energy selectively from a storage state to a target state. The existence of saturation for cross section with the increase of the laser intensity shows that the high-intensity redistribution of transition probabilities is an important feature of this process, which is not accounted for in a two-state treatment. [ABSTRACT FROM AUTHOR]

In order to obtain a high output energy from a xenon lamp-pumped solid-state dye laser, homogeneities of laser mediums and flatnesses of medium faces with different processing treatments are discussed in the paper. The mediums without aging treatment, which are prepared by using a prepolymer process and have diamond-machined end faces to produce the required optical finish, give a highest laser output of 281.9 mJ with 0.215% slope efficiency at 2.0×10-4 mol/L. The best medium lifetime is 21 shots to 50% of original output equating 74.6 kJ/liter. [ABSTRACT FROM AUTHOR]

The solid-state medium containing pyrromethene 567 (PM567) in a polymethylmethacrylate polymer host is shown to lase under the flash lamp excitation. The experimental setup is an ordinary industrial product without special design. The bulk transmission losses, the output energy, and the other lasing properties are compared. The medium with the lowest transmission loss, measured to be 0.392 %/cm at 633 nm, gives a laser output of 130 mJ with a slope efficiency of 0.082%. [ABSTRACT FROM AUTHOR]

This paper studies the molecular rotational excitation and field-free spatial alignment in a nonresonant intense laser field numerically and analytically by using the time-dependent Schrödinger equation. The broad rotational wave packets excited by the femtosecond pulse are defined in conjugate angle space, and their coefficients are obtained by solving a set of coupled linear equations. Both single molecule orientation angles and an ensemble of O2 and CO molecule angular distributions are calculated in detail. The numerical results show that, for single molecule highest occupied molecular orbital (HOMO) symmetry σ tends to have a molecular orientation along the laser polarization direction and the permanent dipole moment diminishes the mean of the orientation angles; for an ensemble of molecules, angular distributions provide more complex and additional information at times where there are no revivals in the single molecule plot. In particular, at the revival peak instant, with the increase of temperature of the molecular ensemble, the anisotropic angular distributions with respect to the laser polarization direction of the πg orbital gradually transform to the symmetrical distributions regarding the laser polarization vector and for two HOMO configurations angular distributions of all directions are confined within a smaller angle when the temperature of the molecular ensemble is higher. [ABSTRACT FROM AUTHOR]

Using a neutral N2 beam as target, this paper studies the dissociation of N+2 in intense femtosecond laser fields (45 fs, [?]1 x 1016 W/cm2) at the laser wavelength of 800 nm based on the time-of-flight mass spectra of N+ fragment ions. The angular distributions of N+ and the laser power dependence of N+ yielded from different dissociation pathways show that the dissociation mechanisms mainly proceed through the couplings between the metastable states (A, B and C) and the upper excited states of N+2. A coupling model of light-dressed potential energy curves of N+2 is used to interpret the kinetic energy release of N+. [ABSTRACT FROM AUTHOR]

This paper investigates the phenomenon of stochastic resonance in a single-mode laser driven by time-modulated correlated coloured noise sources. The power spectrum and signal-to-noise ratio R of the laser intensity are calculated by the linear approximation. The effects caused by noise self-correlation time t1, t2 and cross-correlated time t3 for stochastic resonance are analysed in two ways: t1, t2 and t3 are taken to be the independent variables and the parameters respectively. The effects of the gain coefficient G and loss coefficient K on the stochastic resonance are also discussed. It is found that besides the presence of the standard form and the broad sense of stochastic resonance, the number of extrema in the curve of R versus K is reduced with the increase of the gain coefficient G. [ABSTRACT FROM AUTHOR]

Compared with the metal antenna metasurface, the dielectric metasurface has better optical characteristics and smaller ohmic loss in the optical band, which makes it superior. An elliptical cylindrical nanostructured antenna is designed using GaP with excellent transmission characteristics in the visible band. This structure has a transmission efficiency of up to 0.96 in the visible light band. Based on the Pancharatnam–Berry (PB) phase control principle, the metasurface structure composed of the antennas is studied, and its abnormal refraction metasurface and focusing meta-lens are analyzed. It is a highly efficient sub-wavelength structure, and promises great potential for the applications of circular polarization optics, nanolithography, dense storage and biophotonics. [ABSTRACT FROM AUTHOR]

The structures and the phase transitions of ScH3 under high pressure are investigated using first-principles calculations. The calculated structural parameters at zero pressure agree well with the available experimental data. With increasing pressure, the transition sequence hcp (GdH3-type)→C2/m→fcc→hcp (YH3-type) →Cmcm of ScH3 is predicted first; the corresponding transition pressures at 0 K are 23 GPa, 25 GPa, 348 GPa, and 477 GPa, respectively. The C2/m symmetry structure is a possible candidate but not a good one as the intermediate state from hexagonal to cubic in ScH3. On the other hand, via the analysis of the structures of hexagonal ScH2.9, cubic ScH3, and cubic ScH2, we find that the repulsive interactions of H-H atoms must play an important role in the transition from hexagonal to cubic. [ABSTRACT FROM AUTHOR]

The thermal effect and the heat generation in diode-end-pumped continuous-wave 914-nm Nd:YVO4 lasers are investigated in detail. A theoretical model of a diode end-pumped solid-state laser is constructed to analyse the influence of fractional thermal loading on the thermal effect in the Nd:YVO4 laser based on finite element analysis. The thermal focal lengths and the end-surface deformations of laser rods in Nd:YVO4 quasi-three-level and four-level lasers are measured and compared with the results obtained by ordinary interferometry for the demonstration of higher thermal loading in 914-nm laser. Finally the fractional thermal loading in the Nd:YVO4 quasi-three-level laser is calculated by matching the experimental and the simulated end deformations. [ABSTRACT FROM AUTHOR]

By considering the relative velocity distribution function and multipole expansion interaction Hamiltonian, a three-state model for calculating the cross section of laser-induced quadrupole--quadrupole collisional energy transfer is presented. Calculated results in Xe--Kr system show that in the present system, the laser-induced collision process occurs for [?]4 ps, which is much shorter than the dipole--dipole laser-induced collisional energy transfer (LICET) process. The spectrum of laser-induced quadrupole--quadrupole collisional energy transfer in Xe--Kr system has wider tunable range in an order of magnitude than the dipole--dipole LICET spectra. The peak cross section decreases and moves to the quasi-static wing with increasing temperature and the full width at half peak of the profile becomes larger as the system temperature increases. [ABSTRACT FROM AUTHOR]

Under a nonresonant condition, we theoretically investigate hybrid absorptive-dispersive optical bistability and multistability behaviours in a three-level D-type system by using a microwave field to drive a hyperfine transition between two upper excited states inside a unidirectional ring cavity. We find that the optical bistability and multistability behaviours can be controlled by adjusting the intensity of the microwave field or the intensity of the coherent coupling field. Furthermore, our studies show an interesting phenomenon of the transition from the optical bistability to the optical multistability only by changing the negative detuning of the coupling field into the positive detuning of the coupling field. [ABSTRACT FROM AUTHOR]

The four-level model of laser-induced collisional energy transfer (LICET) for the ion-ion collision system is established based on the time-dependent Schrodinger equation for the electron dynamics, through which the equations of motion of the probability amplitudes and cross section of the collision system are obtained. Numerical calculations are performed for the Ca+-Sr+ system, with the results showing that the peak of the LICET spectrum appears at a resonant frequency of the transfer laser. The magnitude of the obtained collision cross section is in the order of 10[?]16 cm2, and is comparable to that obtained in atomic systems, which indicates the validity of the established four-level model. [ABSTRACT FROM AUTHOR]

Intensive blue photoluminescence (PL) was observed at room temperature from the nanocrystalline-Si/SiO2 (nc-Si/SiO2) multilayers (MLs) obtained by thermal annealing of SiO/SiO2 MLs for the first time. By controlling the size of nc-Si formed in SiO sublayer from 3.5 to 1.5 nm, the PL peak blueshifts from 457 to 411 nm. Combining the analysis of TEM, Raman and absorption measurement, this paper attributes the blue PL to multiple luminescent centres at the interface of nc-Si and SiO2. [ABSTRACT FROM AUTHOR]

Taking the self-gravitation interaction and energy conservation, charge conservation and angular momentum conservation into account, we discuss the tunnelling characteristics of the charged particle from Sen black hole by the Hamilton-Jacobi method. The result shows that the tunnelling probability is related to the change of Bekenstein-Hawking entropy, and the actual radiation spectrum deviates from the pure thermal one, which is consistent with the result of Parikh and Wilczek and gives a new method to correct the Hawking pure thermal spectrum of Sen black hole. [ABSTRACT FROM AUTHOR]

3D aligned-carbon-nanotubes (ACNTs)@Li2FeSiO4 nanocomposite arrays on Al foil were developed as cathode materials for Li-ion batteries. The ACNTs were grown directly on an Al foil by a chemical vapor deposition method to achieve a 3D current collector structure for direct charge transport. Li2FeSiO4 nanoparticles were deposited on the surface of the ACNTs by a polyvinylalcohol (PVA)-assisted sol–gel method. The 3D samples showed a high degree of alignment of nanotubes with a favorable pore morphology before and after cycling. According to electrochemical measurements, the 3D sample with optimized mass ratio of ACNTs and Li2FeSiO4 (2:1) showed excellent rate capability and capacity retention, delivering a discharge specific capacity of 142 mAh g−1 at a rate of 0.5 C (C = 160 mAg−1) and maintaining 99% of the initial discharge capacity after 50 cycles at 24 ° C. Up to 20 C, the delivered charge/discharge capacity was 94 mAh g−1 after 172 cycles, which is 54% of the value obtained at C/20 (175 mAh g−1). In comparison, carbon coated nanoporous Li2FeSiO4 obtained under analogous conditions by a PVA-assisted sol–gel method can only deliver a capacity of 80 mAh g−1 and showed poor rate capability. In addition, despite amorphization, dissolution and chemical composition changes occurring in the 3D samples upon extended cycling, the 3D samples showed good long-term cycling stability at a high current density (5 C), maintaining ∼80% of the initial discharge capacity after 1000 cycles and ∼70% after 2000 cycles. [ABSTRACT FROM AUTHOR]

Femtosecond time-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy is used to investigate gaseous molecular dynamics. Due to the spectrally broad laser pulses, usually poorly resolved spectra result from this broad spectroscopy. However, it can be demonstrated that by the electronic resonance enhancement optimization control a selective excitation of specific vibrational mode is possible. Using an electronically resonance-enhanced effect, iodine molecule specific CARS spectroscopy can be obtained from a mixture of iodine-air at room temperature and a pressure of 1 atm (corresponding to a saturation iodine vapour as low as about 35 Pa). The dynamics on either the electronically excited state or the ground state of iodine molecules obtained is consistent with previous studies (vacuum, heated and pure iodine) in the femtosecond time resolved CARS spectroscopy, showing that an effective method of suppressing the non-resonant CARS background and other interferences is demonstrated. [ABSTRACT FROM AUTHOR]

This paper proposes a novel one-colour Xe-Kr laser induced collisional ionization system. Considering the level scheme of the system, it finds that the initial state of the reaction-the four 4f levels with even J of Xe-can be prepared through method of four-photon resonant excitation by dye laser with wavelength of [?]440 nm. Absorption of an additional photon (the transfer laser) of the same wavelength will complete the laser induced collisional ionization process. The resonance enhanced ionization spectrum of Xe by four laser photons at [?]440 nm is measured through time-of-flight mass spectrometry, this aims at the preparation of the initial state of the system proposed. The Stark broadening of the measured spectrum is observed and consistent with the previous study. Analysis of the measured resonance ionization spectrum implies the feasibility of [?]440 nm four-photon resonant excitation of the initial 4f state of the Xe-Kr system proposed in this paper, which prepares for a further experiment of laser induced collisional ionization. [ABSTRACT FROM AUTHOR]

Polymers are a kind of attractive hosts for laser dyes due to their high transparency in both pumping and lasing ranges and superior optical homogeneity. In this paper solid dye samples based on polymethyl methacrylate (PMMA) doped with different concentrations of 1, 3, 5, 7, 8-pentamethyl-2, 6-diethylpyrromethene-BF2 (PM567) are prepared. The absorption, fluorescence and lasing spectra of the samples are obtained. Wide absorption and fluorescence bands are obtained and a red shift of the maxima of the lasing emission spectra is observed. With the second-harmonic generation of Q-switched Nd:YAG laser (532 nm, [?]20ns) pumping the samples longitudinally, the slope efficiencies of the samples are obtained. There is an optimal dye concentration for the highest slope efficiency when the pumping energy is lower than some typical value ([?]250 mJ), and the highest slope efficiency 35.6% is obtained in the sample with a dye concentration of 2 × 10[?]4 mol/L. Pumping the samples at a rate of 10Hz with a pulse energy as high as 200 mJ (the fluence is 0.2 J/cm2), the output energy drops to one-half of its initial value after approximate 15500 pulses and the normalized photostability is 5.17 GJ/mol. A kind of solid dye laser which could have some applications is built. [ABSTRACT FROM AUTHOR]

Nanocrystalline Si/SiO2 multilayers are prepared by thermally annealing amorphous Si/SiO2 stacked structures. The photoluminescence intensity is obviously enhanced after hydrogen passivation at various temperatures. It is suggested that the hydrogen trapping and detrapping processes at different temperatures strongly influence the passivation effect. Direct experimental evidence is given by electron spin resonance spectra that hydrogen effectively reduces the nonradiative defect states existing in the Si nanocrystas/SiO2 system which enhances the radiative recombination probability. The luminescence characteristic shows its stability after hydrogen passivation even after aging eight months. [ABSTRACT FROM AUTHOR]

Laser dye coumarin 440(C440) is codoped with pyrromethene 567 (PM567) into polymethyl methacrylate (PMMA). The effects of C440 concentration on the performance of the solid state dye medium, including spectra property, slope efficiency and photostability, are studied. When C440 is codoped with PM567 at the same concentration 1 × 10[?]4 mol/L, the highest efficiency and photostability can be obtained. Compared with the medium based on pure PM567 doped PMMA, about 50% increase in slope efficiency and at least five-fold enhancement in the photostability are observed. [ABSTRACT FROM AUTHOR]

Polymers are a kind of attractive hosts for laser dyes because of their superior optical homogeneity, and high transparency in pumping and lasing range. Copolymers usually have higher damage threshold and better photostability than mono-polymers. Solid dye samples based on copolymer of methyl methacrylate (MMA) with 2-hydroxypropyl methacrylate (HPMA) doped with 1-, 3-, 5-, 7-, 8-pentamethyl-2, 6-diethylpyrromethene-BF2 (PM567) are prepared. Spectra and lasing properties of the samples are studied. Compared to the samples based on monopolymer polymethyl methacrylate (PMMA), enhanced slope efficiency and photostability are obtained in the copolymers. The highest slope efficiency is 45.1%, and nearly one-fold increase of photostability is obtained. The longest useful lifetime of 4390 pumping pulses is presented with the pump energy as high as 183 mJ per pulse at repetition rate of 10 Hz. The results indicate that the laser performances of solid dye mediums can be greatly increased using copolymer of MMA with HPMA as host. [ABSTRACT FROM AUTHOR]

Solid-state samples based on modified polymethyl methacrylate (MPMMA) with methanol doped with the dye pyrromethene 650 (PM650) are prepared. The effects of a volume percentage of methanol on the laser characteristics of the sample, including spectra properties, slope efficiency, photostability and tunable properties, are investigated. The broadband dye laser output wavelength is around 655 nm and a highest slope efficiency of 32.23% is achieved. Pumping the samples at a repetition rate of 5 Hz with a pulse energy of as high as 100 mJ (the fluence is 0.26 J/cm2), the longest lifetime (168000 shots) is obtained in the sample (MMA:methanol=18:2), and the corresponding normalized photostability reaches 109.19 GJ/mol. When the sample (MMA:methanol=18:2) is placed in a Shoshan-type oscillator, the narrow-linewidth operation is a continuous tuning range (up to 64 nm). The results indicate that the laser characteristics of solid-state dyes can be greatly enhanced by using modified PMMA with methanol serving as the solid host. [ABSTRACT FROM AUTHOR]