Theoretical analysis and experimental investigation of pulsed tunable forsterite laser

Ｔｈｅｏｒｅｔｉｃａｌａｎａｌｙｓｉｓａｎｄｅｘｐｅｒｉｍｅｎｔａｌｉｎｖｅｓｔｉｇａｔｉｏｎｏｆｐｕｌｓｅｄｔｕｎａｂｌｅｆｏｒｓｔｅｒｉｔｅｌａｓｅｒ￥ＷＵＦｕｓｈｕｎ；ＷＵＸｉｎｇ；Ｂ．Ｈａｍｉｌｔｏｎ；ＹＡＯＪｉａｎｑｕａｎ（ＰｈｙｓｉｃｓＤ...     

紫外激光消融有机物的理论和实验研究

本文分析了紫外准分子激光对有机材料的消融过程,用理论模型解释了每个激光脉冲对有机材料的消融量与入射激光能量密度之间的关系.对于有机玻璃.当入射激光能量密度较高时,双光子过程将起主要作用.最后讨论了消融率随有机材料吸收系数之间的关系,对吸收系数较小的材料,消融率随吸收系数改变有一个极大值.     

Theoretical and experimental investigation of a quenched cavity laser with saturable absorber

Received: 14 April 1997/Revised version: 11 August 1997     

Theoretical and experimental investigation of a waveguide CO2 laser with radio-frequency excitation

A comprehensive experimental and theoretical study of the optimization of a continuous-wave radiofrequency (rf) excited CO₂ waveguide laser is presented. The numerical simulation includes the modelling of the gas-discharge plasma parameters like the plasma impedance and energy deposition, the laser kinetics and finally the influence of the resonator feedback on the lasing process. Along with this theoretical study, an extensive experimental research program enabled us to optimize the laser performance of the CO₂ waveguide laser. As a result, a total output power of 42 W and a specific output power of 1.1 W/cm were obtained.     

Theoretical investigation into spectral characteristics of a semiconductor laser with dual-FBG external cavity

A new theoretical model of the dual-FBG external cavity based on the couple-mode theory has been proposed for controlling the output spectral characteristics of the semiconductor laser with dual-FBG external cavity. The output spectral characteristics have been studied through the analyses of the external cavity length, the FBG length and the fiber length between the two FBGs. The results reveal that the side mode suppression ratio (SMSR), the full wave at half maximum (FWHM), the longitudinal mode interval (LMI) and the stability of the central wavelength are mainly determined by the effective external transmissivity, the fiber length between the two FBGs and the external cavity length, respectively. Furthermore, the rising/falling tendencies of the SMSR and the FWHM are exactly opposite. There exist the maximum of the SMSR and the minimum of the FWHM in a semiconductor laser with dual-FBG external cavity. The increase of the fiber length between the two FBGs results in the exponential decrease of the LMI. The increase of the external cavity length leads to the better stability of the central wavelength.     

Theoretical and experimental investigation of thermal effects in a high power Yb-doped double-clad fiber laser

In this paper, based on the thermal conduction equations and the steady-state rate equations, a theoretical and numerical analysis of thermal effects is investigated for a single end pumped Yb-doped double-clad fiber laser (YDDC). The distributions of signal power and temperature for different pump powers and fiber parameters are compared. According to the results, the parameters of the optical-cavity have been optimized and an effective method has been adopted to reduce the thermal effects in an experimental investigation. As a result, an output power of 621 W has been obtained with a slope efficiency of 78%.     

Numerical and experimental investigation of laser propulsion

Aiming at the application of laser propulsion to stratospheric flight, we propose here a repetitive propulsion system, friction-less environment and metal-free ablation in a water cannon target. A special reservoir of water is proposed to supply a definite amount of water only at the time of laser irradiation. This system is tested for the object levitated on the airflow, which is called air-slider in order to simulate friction-less environment. In order to avoid the evaporation and freezing of water in lower atmospheric pressures, we propose here an air curtain system. We have performed simulations and experiments and confirmed that a small amount of air flow can sustain the high pressure inside the water reservoir. PACS 42.62.Cf; 52.38.Mf; 07.87.+v     

W掺杂ZnO透明导电薄膜的理论及实验研究

本文从理论与实验两方面入手, 对高价态差金属W掺杂ZnO (WZO) 薄膜材料的特性进行分析讨论. 采用基于密度泛函理论的平面波赝势方法对WZO材料特性进行理论分析, 计算结果表明: W以替位形式掺入ZnO六角纤锌矿晶格结构中, 由于W-O键的键长较长引起晶格常数增加, 产生晶格畸变; 掺杂后费米能级进入导带, 其附近的导电电子主要由W 5d, O 2p及Zn 3d电子轨道提供, 材料表现出n型半导体的特性; 同时能带简并效应使其光学带隙展宽. 为进一步验证该理论分析结果的适用性, 本文采用脉冲直流磁控溅射技术进行了本征ZnO及WZO薄膜的实验研究, 结果表明: W掺入未改变ZnO的生长方式, 但引起薄膜的晶格常数增加, 电阻率由本征ZnO的1.35× 10^-2 Ω·cm减小到1.55× 10^-3 Ω·cm, 光学带隙由3.27 eV展宽到3.48 eV. 制备的WZO薄膜在400-1100 nm的平均透过率大于83%. 实验结果对理论计算结果进行了验证, 表明WZO薄膜作为透明导电薄膜的应用潜力.     

Theoretical and experimental investigation of x-band two-cavity gyroklystron

Using self-consistent field theory, the interaction of electron flow with HF fields in a gyroklystron has been analized. Optimal parameters of its output cavity corresponding to the maximum efficiency have been found. Experimental study of dependence of the efficiency on Q-factor and length of the output cavity has been carried out. The results of simulation are in good qualitative agreement with experimental data.     

316L不锈钢粉末光纤激光选区熔化特性

采用自行研制的光纤激光选区熔化快速成型设备,研究了选区激光熔化316L不锈钢粉末工艺参数、能量输入与样件致密度、表面形貌之间的关系以及微观组织特征。结果表明:扫描速度对成型效果影响最为显著;样件致密度随着激光能量密度提高有逐渐增大的趋势;能量密度作为选区激光熔化工艺的技术指标具有可操作性;表面形貌由激光功率与扫描速度比值所决定。深入探讨了能量输入、熔化凝固行为、激光功率与扫描速度比值与样件致密度、表面形貌的关系。结果表明:选区激光熔化凝固组织层内、层间熔合处为弧形,且为冶金结合,金相组织主要由柱状晶与等轴晶组成,层内靠近熔合线周围是柱状晶,而层间靠近熔合线附近主要是细小等轴晶,晶粒直径为1μm左右。     

316L不锈钢粉末光纤激光选区熔化特性

采用自行研制的光纤激光选区熔化快速成型设备,研究了选区激光熔化316L不锈钢粉末工艺参数、能量输入与样件致密度、表面形貌之间的关系以及微观组织特征。结果表明：扫描速度对成型效果影响最为显著;样件致密度随着激光能量密度提高有逐渐增大的趋势;能量密度作为选区激光熔化工艺的技术指标具有可操作性;表面形貌由激光功率与扫描速度比值所决定。深入探讨了能量输入、熔化凝固行为、激光功率与扫描速度比值与样件致密度、表面形貌的关系。结果表明：选区激光熔化凝固组织层内、层间熔合处为弧形,且为冶金结合,金相组织主要由柱状晶与等轴晶组成,层内靠近熔合线周围是柱状晶,而层间靠近熔合线附近主要是细小等轴晶,晶粒直径为1 μm左右。     

An experimental investigation into the icing and melting process of a water droplet impinging onto a superhydrophobic surface

The freezing and melting process of a small water droplet on a superhydrophobic cold surface was investigated using the Laser Induced Fluorescence (LIF) technique. The superhydrophobic surface was prepared using a sol-gel method on a red copper test plate. From the obtained fluorescence images, the phase transition characteristics during the freezing and melting process of a water droplet were clearly observed. It was found that, at the beginning of the droplet freezing process, liquid water turned into ice at a very fast rate. Such phase transition process decreased gradually with time and the volume of frozen ice approached a constant value at the end of the icing process. In addition, the freezing time was found to reduce with the decrease of the test plate temperature. Besides, when the test plate temperature is relatively high, the effect of droplet volume on the freezing time is very significant. Over all, we provide some tentative insights into the microphysical process related to the icing and melting process of water droplets.     

Theoretical and experimental analysis of high power diode laser (HPDL) hardening of AISI 1045 steel

Laser surface hardening makes use of the rapid and cooling cycles produced on metals surfaces exposed to a scanning laser beam without affecting the bulk of the sample. Mechanical and chemical properties of the surface can be enhanced through the metallurgical transformations that take place during the mentioned thermal cycles. Steels and cast irons are the usual materials to be hardened by laser and recently the high power diode lasers (HPDL) became the appropriate tool to carry out this process. In this work, some systematic experiments have been carried out to harden AISI 1045 surface samples by a cw (HPDL) working at different power levels (470, 760 W). The main processing parameters (scanning velocity and density power of the laser beam) were tuned from the prediction realized by the numerical (ANSYS) analysis of the heat conduction involved in the process. Such analysis allowed us to put in evidence the variation of the temperature and the cooling rate of the steel sample surface, affecting the uniformity of the demanding mechanical properties of the surface. In this way, a close-loop temperature control of the surface was justified in order to keep the hardness value within the range required. The formation of martensite phase in the laser treated superficial zone confirmed the hardening of the steel.     

Nanosecond pulse laser melting investigation by IR radiometry and reflection-based methods

Experimental system for nanosecond laser melting investigation was developed containing three independent noncontact methods: infrared radiometry, time-resolved reflectivity of He-Ne laser and sample surface reflected KrF heating laser pulse. The system was applied to the investigation of laser melting of Cu, Mo, Ni, Si, Sn, Ti, steel ?SN 15330 and stainless steel ?SN 17246 samples. For metallic samples the IR radiometry signal was transformed to temperature. Obtained surface temperature and reflectivity spectra in nanosecond time scale (10-1000 ns) for wide range of energy densities (100-5500 mJ cm⁻²) are presented. Interesting evolutions were found. Melting thresholds and melting durations were determined from the measured curves. The applicability of the methods is evaluated.     

Theoretical and experimental investigation into the influence of the periodic backlash fluctuations on the gear rattle

The paper provides an investigation into the influence of the periodic variation in the boundaries of the dead-zone between the teeth, caused by the Transmission Error, on the gear rattle phenomenon.The study represents an evolution of a theoretical model, which has already been developed by the authors, to analyze lightly loaded gear pairs, accounting for oil squeeze effects between the gear teeth.An experimental test rig and a methodology to estimate the transmission error parameters, starting from an experimental acquisition, are described.A number of experimental-theoretical correlations concerning the influence of transmission errors on gear dynamics are reported in order to validate the theoretical model.     

Microstructure and properties of high chrome steel roller after laser surface melting

Laser surface melting of high chrome steels was achieved by a 5 kW continuous wave CO₂ laser. The microstructure of the laser surface-melted steels was investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffractometry, and the hardness profiles were determined by a Vickers hardness tester. The corrosion behavior in 3.5% NaCl solution was studied by electrochemical corrosion equipment. The large carbides of high chrome steels are completely dissolved and ultrafine dendrites of austenite with submicroscopic M₂₃C₆ carbides precipitation are formed in the melted zone. The austenite in the melted zone has a high tempering stability. The corrosion resistance of the laser surface-melted steels is significantly improved due to the dissolution of carbides and the increase of the alloying elements in the solid solution as well as the large amount of austenite.     

Theoretical and experimental basis of biostimulation by laser irradiation

A physical model is described to explain the biostimulating effect of a laser beam. It is proposed that polarization is responsible, with the unidirectional electromagnetic field reorienting the lipid bilayer in the cell membrane. A light source which emits linearly polarized light has been made and used in clinical trials.     

Theoretical and experimental investigation of electron-beam-controlled synthesis of nitrogen-containing compounds

A theoretical and experimental investigation is made of the electron-beam-controlled method of synthesizing nitrogen-containing compounds. It is shown that the basic chemically active form of nitrogen in the electron-beam-controlled discharge are the vibrationally excited molecules N₂. The experimental procedure and the results are meported on the synthesis of nitrogen oxides, hydrogen cyanide, and phosphorus nitride. The isotopic compositions of the vibrationally excited nitrogen and carbon monoxide are calculated.Translated from Trudy Ordena Lenina Fizicheskogo Institute im. P. N. Lebedeva, Vol. 116, pp. 146–180, 1980.