Theoretical study on line source laser-induced surface acoustic waves in two-layer structure in ablative regime

The generation of ultrasound in film–substrate system by a laser line source is studied in the case of ablation mechanism, which can be realized by adding a liquid layer at the excitation point. The time domain displacement can be yielded by the numerical jointed inversed Laplace–Fourier transformation technique. The typical surface acoustic waves (SAW) of two layer structures, slow film on fast substrate and fast film on slow substrate, are obtained and the effect of the propagation distance and the thickness of the film on the SAW are given.     

Development of a novel high speed (electron-mobility) epi-n-ZnO thin films by L-MBE for III–V opto-electronic devices

Intrinsic epitaxial zinc oxide (epi-ZnO) thin films were grown by laser-molecular beam epitaxy (L-MBE), i.e., pulsed laser deposition (PLD) technique using Johnson Matthey “specpure”-grade ZnO pellets. The effects of substrate temperatures on ZnO thin film growth, electrical conductivity (σ), mobility (μ) and carrier concentration (n) were studied. As well as the feasibility of developing high quality conducting oxide thin films was also studied simultaneously. The highest conductivity was found for optimized epi-ZnO thin films is σ=0.06×10³ ohm⁻¹ cm⁻¹ (n-type) (which is almost at the edge of semiconductivity range), carrier density n=0.316×10¹⁹ cm⁻³ and mobility μ=98 cm²/V s. The electrical studies further confirmed the semiconductor characteristics of epi-n-ZnO thin films. The relationship between the optical and electrical properties were also graphically enumerated. The electrical parameter values for the films were calculated, graphically enumerated and tabulated. As a novelty point of view, we have concluded that without doping and annealing, we have obtained optimum electrical conductivity with high optical transparency (95%) for as deposited ZnO thin films using PLD. Also, this is the first time that we have applied PLD made ZnO thin films to iso-, hetero-semiconductor–insulator–semiconductor (SIS) type solar cells as transparent conducting oxide (TCO) window layer. We hope that surely these data be helpful either as a scientific or technical basis in the semiconductor processing.     

Geometrically qualified ESPI vibration analysis of an engine

This paper presents an application in the automotive industry where a combination of electronic speckle-pattern interferometry and laser doppler velocimetry were used at a critical stage in the design process of an internal combustion engine. Combined deformation and surface relief measurements were used to study the phase and amplitude of deformation of a vibrating engine. The relief data was combined with the interferometer geometry and used to geometrically correct the deformation data, in an effort to improve accuracy. The measurements allowed rapid identification and quantification of design weaknesses, particularly those causing undesirable resonances. This led to a significant reduction in the design time and lowering of costs, when compared with existing design optimisation methods.     

双环掺铒光纤激光器混沌偏振控制方法研究

提出双环掺铒光纤激光器激光混沌的偏振耦合控制以及部分偏振控制方法,偏振耦合控制能控制耦合相互作用以控制激光混沌,部分偏振控制是控制部分偏振耦合效应以控制激光混沌.数值模拟了偏振耦合控制混沌和某一个环的部分偏振控制混沌,它们都能实现把双环掺铒光纤激光器激光混沌控制到稳定态和周期态上;通过实时调控光的偏振方向,这两种混沌控制方法都能实时地、动态地、有效地控制激光混沌进入到稳定态和周期态上.     

激光导致水击穿和等离子体形成过程的物理分析

对短脉冲激光作用水介质中引起光学击穿的机制进行了分析,通过自由电子密度速率方程的数值解确定激光的击穿阈值.将数值计算结果与波长在可见光和近红外波段,脉宽为ns、ps和fs的激光脉冲在纯净水和含有杂质的水中的实验测量的击穿阈值作了比较.还计算了等离子体中自由电子密度的演化、等离子体吸收系数和能量密度.通过解自由电子密度速率方程得到结果与实验测量的值符合得很好.     

Determination of line strengths for selected transitions in the v2 band relative to the v1 and v5 bands of H2CO

The spectral line strengths in the v₂ band of H₂CO (segments spanning 1720-) have been determined relative to two sets of spectral line groups in the v₁ and v₅ band, using tunable diode laser spectroscopy. Simultaneous detection using a dual-diode instrument with a absorption cell was employed to assure identical H₂CO column density for the two spectral regions. The results in the selected regions of this study are in good agreement with the line positions and the relative intensities specified in an unpublished complete line listing for the v₂ band prepared by Linda Brown (see full text for reference). Based upon measurements of individual groups of spectral lines in the P, Q and R branches, the absolute band strength has been determined to be .     

Thermal fields in laser–multi-layer structures interaction

In the present paper, we are dealing with the thermal fields for laser–periodic multilayer structures interaction. Our point of view is originally that we consider any order transverse laser beams, like heating sources. We consider that the laser beam acts in IR (Nd:YAG or CO₂ laser beam) and it is in one transverse mode or in only a few decoupled modes. In order to solve this problem, we will use the Green function method. Specific results are presented for a laser beam (Nd:YAG laser) operating in the mode TEM₀₁ and a two-layer structure.     

Study of the conditions for the effective energy transfer in a process of acceleration and collision of the thin metal disks with the massive target

Efficiency studies of laser driven thin metal disks acceleration using the first harmonic (λ₁=1.315 μm) of the Prague Asterix Laser System (PALS) and subsequent craters creation produced by collisions of these disks with massive targets are presented. Several different disks made of aluminium and copper foils with diameters of 300 μm and 600 μm and thicknesses of 11 μm (Al) and 3.6 μ m (Cu) were employed. Disks were placed at the distance of either 100 μ m or 300 μm in front of aluminium massive targets. The following irradiation conditions were used: the laser beam energy of 120 J, the focal spot diameter of 200 μm, and the pulse duration of 0.4 ns (FWHM). A three-frame interferometric system was employed to determine electron density distributions in plasma corona. Shape and volume of craters were obtained by crater replica technology and microscopy measurements. The aim of these investigations was to analyse conditions leading to the most effective energy transfer in the process of collision of the accelerated disks with solid targets. The overall efficiency of these processes was characterized by the volume of craters produced in such targets.     

The characteristics of confined ablation in laser propulsion

Compared with direct ablation, confined ablation provides an effective way to obtain a large target momentum and a high coupling coefficient. By using a transparent glass layer to cover the target surface, the coupling coefficient is enhanced by an order of magnitude. With the increase of the gap width between the target surface and the cover layer, the coupling coefficient exponentially decreases. It is found that the coupling coefficient is also related to the thickness of the cover layer.     

Frequency-tripled Nd:YAG laser ablation in laser structuring process

With the increasing demand for finer lines/spaces on PCB boards, a new technology—laser structuring—has emerged in recent years. In this research, the frequency-tripled Nd:YAG laser is selected as the laser source in laser structuring; this laser is often used in miniaturization machining. This paper describes in detail the processing parameters’ influences, such as laser power, numbers of repetition, repetition rate and bite size, on laser structuring results. From the research results, it can be concluded that the line width and depth are increased with increases in the laser power and numbers of repetition. Repetition rate, bite size and velocity are related to one another. When the bite size is fixed, the velocity increases with the repetition rate and the depth of the line is decreased at the same time. When the repetition rate is fixed, velocity increases with the bite size.