CO2激光器五种混合气体压强优化

 应用遗传算法,以输出激光功率为目标函数,优化确定了普通CO₂激光器五种工作气体（CO₂, N₂, He, Xe, H₂）的最佳充气量。对1.2m长谐振腔,在15kV放电条件下,优化的充气量分别为p_CO2=1.15×133.3Pa, p_N2=7.32×133.3Pa, p_He=12.95×133.3Pa, p_Xe=0.36×133.3Pa和p_H2=0.01×133.3Pa。优化后激光功率比未优化前可提高1.27倍。     

合肥上空大气二氧化碳Raman激光雷达探测研究

Raman激光雷达是用于大气成分探测与特性研究的有效工具.介绍了中科院安徽光学精密机械研究所自行研制的一台用于测量低对流层大气CO₂时空分布的Raman激光雷达系统,并进行了一系列观测实验和对比分析.系统选用波长355 nm的紫外激光作为光源,利用光子计数卡双通道采集大气中N₂和CO₂的Raman后向散射信号与Li-7500型H₂O/CO₂分析仪进行对比标定,通过反演获得了大气CO₂水平与垂直方向时空分布廓线,并且获得了合肥地区大气边界层CO₂的夜变化趋势.结果表明,大气CO₂在空间的分布相对均匀,Raman激光雷达与CO₂分析仪变化趋势一致性较好,能够对大气CO₂时空分布进行有效、连续的观测.     

Laser-induced Alignment and Coulomb Explosion of CO2

实验研究了CO₂分子在飞秒强激光脉冲作用下的动力学过程,包括分子取向,隧穿电离和库仑爆炸,激光强度从1×10¹³W/cm²变化到6×10¹⁴W/cm². 当激光强度小于分子的电离阈值时,CO₂分子的非绝热转动激发形成一个相干转动波包,波包演化导致分子沿激光电场方向取向. 激光脉冲结束后,分子取向可以周期性地再现,利用另一束激光可以对取向结构进一步进行修饰. 当激光强度大于分子     

紧凑的非链式脉冲HF激光器

研究了气体组分和峰化电容对紫外光预电离脉冲HF激光器性能的影响.实验发现最佳气体混合比为SF₆/C₂H₆=20:1,峰化电容和主放电电容的最佳比为C_p/C_s=0.3,在最佳气体混合比时,最大激光脉冲峰值功率和对应的总气压随充电电压的提高而增大.同时得到了E/P值和激光能量的关系.整个器件的最大激光输出为400mJ,脉冲峰值功率为1.5MW,最大电光转换效率约为2.2%.     

1.315μm附近CO2的高分辨率吸收光谱

 利用可调谐激光长程吸收光谱测量系统，记录到1.315μm附近高气压（80kPa和40kPa）CO₂的高分辨率吸收光谱，拟合分析获得谱线参数，结果与HITRAN 2k的数据基本一致。用程差法测量了绝对吸收，氧碘激光频率(7 603.138 5cm^-1)的总吸收截面为(0.23~0.29)×^-24cm²。仅计算谱线吸收的吸收截面为0.18×10^-24cm²。在1.315μm波段COCO₂存在连续吸收，吸收截面为(0.05~0.11)×10^-24cm²。还讨论了测量误差问题。     

特定位点上CO2与(TiO2)n团簇相互作用的第一性原理研究

本文基于密度泛函理论系统地研究了(TiO₂)_n团簇上二氧化碳(CO₂)的吸附和活化性质. 计算结果表明,CO₂更倾向于吸附在(TiO₂)_n团簇的桥氧原子上,形成“化学吸附”碳酸盐络合物. 而CO更倾向于吸附到末端Ti-O的Ti原子上. 发现计算得到的碳酸盐振动频率值与实验获得的结果非常吻合,这表明配合物中CO₂的几何构型与其线性型相比,有微小的弯转. 通过对电子结构、电荷密度、电离势、HOMO-LUMO以及态密度的分析,证实了CO₂与团簇之间的电荷转移以及相互作用. 从预测的能量分布图来看,(TiO₂)_n团簇上的CO₂活化与结构密切有关,相比于块体的TiO₂,CO₂在团簇结构上更易于吸附和活化.     

CO2在Pd表面吸附的热力学

 用密度泛函方法和相对论有效原子实势,分别对PdCO₂,PdCO和PdH的基态几何构型进行优化, 得到PdCO₂分子基态为Cs构型, Pd与CO2分子在同一平面, 键长PdC为0.203 0 nm, CO为0.118 3 nm, CO′为0.121 0 nm, 键角∠OCO′为154.215°,电子状态为1A′; PdCO分子基态电子状态为1+, 键长PdC为0.183 4 nm, CO为0.114 0 nm, 键角∠PdCO为180°; PdH分子基态为2∑, 键长PdH为0.152 6 nm。根据电子-振动近似理论计算了不同温度下金属Pd 与CO₂,CO及H2分子反应的生成热力学函数, 导出了反应平衡压力随温度的变化关系。分析认为杂质CO₂气体引起Pd合金膜中毒可能是由于CO₂分子吸附在Pd膜表面,形成Pd的CO₂化合物后,再自发分解为PdO和CO,而使Pd表面出现O和CO中毒所致。     

多晶LaB6阴极的脉冲热发射特性

 采用多晶LaB₆材料制成平板二极管阴极，阳极采用钼材料，阴极采用热传导与热辐射加热，加热体为石墨。实验研究了不同阴极温度、不同真空度下的脉冲发射特性，并对热发射稳定性进行了分析。结果表明： 在动态真空系统中， 阴极发射面积为0.012 1 cm²， 工作真空度为2×10^-4 Pa， 阴极温度分别为1 600， 1 650和1 700 ℃，在脉冲宽度为40 ms、重复频率为107 Hz的条件下，最大脉冲发射电流密度分别为34.0，44.0和53.8 A/cm²; 2×10^-4，5×10^-4和2×10^-3 Pa压强下的发射能力没有明显的差异;脉冲宽度的变化不影响发射电流密度的变化。     

气压对吸气式激光推进冲量耦合系数的影响

 保持CO₂激光的单脉冲能量为61.4~64.6 J，采用高精度冲击摆系统进行了不同气压下吸气模式激光推进冲量耦合系数的实验测试，分析了对应的高度特性。结果表明：气压为2.8×10⁴～1×10⁵ Pa，即距离地面0～10 km时，冲量耦合系数大约3.5×10^-4 N·s·J^-1，上下波动幅度低于5%；气压低于2.8×10⁴ Pa，即高度大于10 km时，冲量耦合系数呈二次曲线显著下降；当气压降至1×10³ Pa，即距离地面约31 km高度时，耦合系数仅为9.7×10-5 N·s·J^-1。     

Cl/HN3/I2全气相化学激光体系的化学动力学模拟计算

 对Cl/HN₃/I₂产生NCl(a)/I激光的过程进行了化学动力学计算，主要考察了Cl,HN₃和I₂的初始粒子数密度及其配比对小信号增益系数的影响。结果发现,当温度为400K, 初始Cl粒子数密度为1×10¹⁵，1×10¹⁶和1×10¹⁷cm^-3时,小信号增益系数分别达到1.6×10^-4,1.1×10^-3和1.1×10^-2cm^-1，获得最佳小信号增益系数的HN₃和I₂的初始粒子数密度分别为初始Cl粒子数密度的1～2倍和2%～4%。同时，对Cl，HN₃和I₂配比对小信号增益系数和增益持续时间的影响进行了讨论。     

Determination of an optimal five-gas combination in a sealed-off CO<Subscript>2</Subscript> laser

For obtaining the maximal output power, five lasing gas mixtures (CO₂, N₂, He, Xe and H₂) in a sealed-off CO₂ laser are optimized by applying a genetic algorithm and solving CO₂ laser kinetics equations. A comparison of numerical simulations shows that the optimal pressures of CO₂ and N₂ are 1.15 Torr and 7.32 Torr, respectively. Accordingly, the maximum laser power of 124 W is obtained by utilizing the optimal gas combination and an optimized resonator with a length of 1.2 m. Received: 14 August 2002 / Published online: 22 January 2003 The project supported by Zhejiang Provincial Natural Science Foundation of China (No. 602098). RID="*" ID="*"Corresponding author. Fax: +86-571/8832-0369, E-mail: chengch@mail.hz.zj.cn     

Multiphoton absorption and luminescence of osmium tetroxide

Both the multiphoton absorption and the luminescence brightness of osmium tetroxide induced by absorption of temporally smooth CO₂ 10P(20) laser pulses of 10 and 40 ns FWHM have been measured for pressures in the range 6.7 to 200 Pa. A dependence of these phenomena on laser pulse length is observed. Comparison of the luminescence brightness to the average excitation shows that the distribution of the multiphoton excitation depends on the laser pulse intensity for the two pulse lengths studied.Issued as AECL Contribution No. 8806     

Study of the parameters of the collisionally broadened R22 absorption line of the 1000-0001 transition in CO2 molecules: I. Experiment

Unsaturated absorption coefficients in pure carbon dioxide at pressures of 1 and 100 Torr and in CO₂-N₂ and CO₂-He binary mixtures at a pressure of 100 Torr have been measured in the temperature range of 296?C700 K using a frequency-stabilized tunable CO₂ laser. The collisional self-broadening coefficient, the relative coefficients of collisional broadening caused by N₂ and He buffer gases, and their temperature dependences have been determined for the R22 absorption line of the 10⁰0?C00⁰1 transition in CO₂ molecules.     

Pressure-broadened iodine-laser-amplifier kinetics and a comparison of diluent effectiveness

An iodine laser kinetic model is used to investigate inversion parameters in highly pressure-broadened amplifier systems using i-C₃F₇I as the parent compound and CO₂, N₂, He, Ne, Ar, Kr, and Xe as the diluent gas. These data are used to calculate a diluent merit function for diluent pressures P_d = 1–100 atm. The most effective choices for buffer gases are as follows: P_d ? 1 atm, CO₂; 1 atm ? P_d ? 10 atm, Ar; and P_d ? 10 atm, Ne.     

Optimization of three gas compositions in a CO2 laser

Three pressures of gases (CO₂, N₂ and He) added into CO₂ laser tube are optimized for obtaining maximal laser output power by applying a genetic algorithm and solving the CO₂ laser kinetics equations. After the optimization, the laser power is increased by 96% as compared with a non-optimal case.     

Construction of a photon drag detector for evaluating the performance of a CO2 laser amplifier

In this article, the construction of P-type germanium (Ge) photon drag detector which is used to characterize the gain and output powers of a 10 W CO₂ laser and a CO₂ laser amplifier is described. Gain and laser amplifier output power versus laser input power measurements collected at 4.7 mbar and 12.0 mbar amplifier tube pressures are discussed. Moreover, measurements relating the CO₂ laser output power to the laser tube discharge current are provided at 6.9 mbar and 7.3 mbar tube pressures.     

Systematic experimental study of instabilities in the sealed CO2 laser

A systematic pressure-current experimental study of the wave instability regions in glow-discharge of different CO₂ laser mixtures has been accomplished. The forward ionization wave F^– has been found to be the main instability. At low currents (< 30 mA) and higher pressures (> 550 Pa) the laser discharge becomes stable. The highest output power at a given mixture ratio was achieved in these quiet regions. The normalized electric field dependences of wavenumber, phase and group velocities of the F^– wave are presented.     

Effect of air pressure on the spatial and emission characteristics of an aluminum laser torch under subthreshold conditions of ablation

The spatial characteristic of an aluminum laser-induced plasma are studied at a laser radiation intensity of (3.8–4.8) × 10⁸ W/cm² and an air residual pressure of 6.7–133.3 Pa. It is found that the duration of the aluminum plasma glow is 50 μs and decreases with decreasing laser power output. The glow intensity reaches a maximum at t = 1.4 μs and rises with laser energy. Typical sizes of the emitting area on the laser torch are determined.     

Interaction of O2, CO2, CO,C2H4 and C2H4O with Ag(110)

The interaction of O₂, CO₂, CO, C₂H₄ AND C₂H₄O with Ag(110) has been studied by low energy electron diffraction (LEED), temperature programmed desorption (TPD) and electron energy loss spectroscopy (EELS). For adsorbed oxygen the EELS and TPD signals are measured as a function of coverage (θ). Up to θ = 0.25 the EELS signal is proportional to coverage; above 0.25 evidence is found for dipole-dipole interaction as the EELS signal is no longer proportional to coverage. The TPD signal is not directly proportional to the oxygen coverage, which is explained by diffusion of part of the adsorbed oxygen into the bulk. Oxygen has been adsorbed both at pressures of less than 10^-4 Pa in an ultrahigh vacuum chamber and at pressures up to 10³ Pa in a preparation chamber. After desorption at 10³ Pa a new type of weakly bound subsurface oxygen is identified, which can be transferred to the surface by heating the crystal to 470 K. CO₂ is not adsorbed as such on clean silver at 300 K. However, it is adsorbed in the form of a carbonate ion if the surface is first exposed to oxygen. If the crystal is heated this complex decomposes into O_ad and CO₂ with an activation energy of 27 kcal/mol(1 kcal = 4.187 kJ). Up to an oxygen coverage of 0.25 one CO₂ molecule is adsorbed per two oxygen atoms on the surface. At higher oxygen coverages the amount of CO₂ adsorbed becomes smaller. CO readily reacts with O_ad at room temperature to form CO₂. This reaction has been used to measure the number of O atoms present on the surface at 300 K relative to the amount of CO₂ that is adsorbed at 300 K by the formation of a carbonate ion. Weakly bound subsurface oxygen does not react with CO at 300 K. Adsorption of C₂H₄O at 110 K is promoted by the presence of atomic oxygen. The activation energy for desorption of C₂H₄O from clean silver is ～ 9 kcal/mol, whereas on the oxygen-precovered surface two states are found with activation energies of 8.5 and 12.5 kcal/mol. The results are discussed in terms of the mechanism of ethylene epoxidation over unpromoted and unmoderated silver.