Highly uniform UV preionized CO2 laser

Highly uniform laser pulses have been obtained in CO₂−N₂−He mixtures, between 1 and 5 atm with the help of true volume pre-ionization by single step photoionization of new additives having a low ionization potential.     

Parametric study of a UV preionized CO2 laser

Small signal gain measurements of a uv preionized TEA CO₂ laser system are described. It is shown that the relative timing of preionization with respect to the main discharge determines the amount of electrical energy that can be deposited in the gas prior to arc formation.     

The operation of the tea CO2 laser with nonconventional CO2/H2 gas mixture

Very strong and efficient emission from TEA CO₂ laser, which operates with nonconventional binary CO₂/H₂ mixture, is obtained. Output pulse energy and power up to 46 mJ and 0.9 MW were achieved, respectively.     

TEA CO2 laser induced breakdown versus selective photochemistry in C2F5H and C2F5H/C2F5T mixtures

In the context of laser separation of tritium isotope using C₂F₅T in mixtures with C₂F₅H, we have studied the laser induced dielectric breakdown (LIDB) as a function of the system pressure using 10.6 μm radiation of a TEA CO₂ laser. By taking also into account our isotope selective results, we have found that LIDB does not imply difficulties by affecting the laser selective process. Analysis of the experimental results shows that LIDB works by cascade ionization and the recombination constitutes the major loss process. The LIDB threshold fluence Φ_th for the tritiated mixture was found to be lower than the corresponding value in pure C₂F₅H indicating preionization in the medium due to β emission of tritium.     

Theoretical and experimental study of V–I characteristics of UV pre-ionized TEA CO2 laser for variety of laser gas mixtures

Experimental and theoretical study of V–I characteristics of UV pre-ionized TEA CO₂ laser has been carried out for a variety of gas mixtures emitting different optical pulse shapes suitable for various applications. Coupled differential equations have been solved to model the pulse excitation circuit using the numerically calculated values of ionization coefficient (α), attachment coefficient (β) and drift velocity (U_d) as functions of E/N (i.e. electric field to neutral particle density ratio) for chosen gas mixture. Calculated and experimental V–I characteristics for gas mixtures (CO₂:N₂:He::1:2:3, 1:1:4, 1:1:5 and 1:0:4.7) show a good agreement. It has been shown that gas mixture has a dominant effect on the delay between pre-ionization and main discharge; thus, determining the long-term stability of discharge. The excitation pulse duration increases with increase in molecular content of gas mixture (i.e. amount of CO₂ and N₂ in gas mixture).     

Spectroscopic study of a TEA CO2 laser of the CO2/X,X=H2; N2/H2 type

The spectral output of a TEA CO₂ laser utilizing nonconventional CO₂/H₂ and CO₂/N₂/H₂ gas mixtures was analysed. A simultaneous multiline output in P-branch of the 00°110°0 transition was recorded. A domination of the P(18) line is typical for the first, and that of the P(20) line for the second gas mixture. The enhancement of the P(18) line intensity in spectra (different from P(20) line domination-CO₂/N₂/H₂ mixture) is explained primarily by a smaller contribution of the R(23) line gain (01¹111¹0 CO₂ band), to P(20) line (00°110°0 band). All measurements were conducted with a nondispersive optical cavity.     

Power scaling of printed-circuit-board preionized TEA CO2 laser up to 3.6 kW

A high average power, high-repetition-rate TEA CO₂ laser employing printed-circuit-board preionizer is described. The power scaling of this preionization configuration has been demonstrated. The average output power reaches 3.6 kW at pulse repetition rate of 180 pps. Furthermore, the scaling-up ability of the rotating spark gap as high-voltage switch for high-average-power gas laser has been validated.     

高功率TEA CO2激光器气体循环系统的设计

阐述了气体循环系统对高功率TEA CO2激光器的重要作用,分析了系统参数、结构组成及其设计。以体积流量法确定放电区气体流速,采用对称式的结构布局,选用轴流压气机和板翅式热交换器,加入系统附加阻力以确定风机静压参数。研究出的气体循环系统,放电区气体平均流速84.8 m/s,流速不均匀度纵向4.2%、横向0.38%;光学支架振动加速度4×10-2 m/s2,振动位移2.6×10-7 m。在放电体积2.5×10-3 m3、单脉冲注入能量276 J、放电脉宽150 ns条件下,实现了重复频率400 Hz均匀稳定的持续辉光放电,输出了高平均功率激光。     

相位板偏振偏转角对径向偏振光的梯度力分布的影响

研究了同心分区偏振偏转相位板对径向偏振光梯度力的调制效应。给出了相位板各部分偏振偏转角不同时,光学梯度力的分布情况。模拟结果表明:随着同心分区相位板各部分的半径和偏振旋转角的改变,光学梯度力方向及大小明显变化,且会产生许多可控的梯度力分布模式,可应用于微粒的收集、分离和合并。结果显示同心分区相位板对径向偏振光的调制可以用来生成可调光镊。     

Miniature high-repetition-rate TEA CO2 laser with surface-wire-corona preionization

In this article, an experimental study of a miniature, sealed-off, high-repetition-rate transversely excited atmospheric-pressure (TEA) CO₂ laser with a kind of surface-wire-corona preionization (SWCP) is described. We have utilized an SWCP consisting of SiO₂ dielectric tube and a fine wire strained and attached to the dielectric surface. A BN ceramic material, which has an extremely low coefficient of thermal expansion of about 5 × 10⁻⁷/°C was employed as a supporter of the resonator. A measurement on emission spectra of SWCP has been reported. By applying SWCP to the TEA CO₂ laser, efficient laser operation at an overall efficiency of 9.8% with an output energy of 150 mJ has been achieved from a small discharge volume of 25 cm³ with an active length of 230 mm. At the pulse repetition frequency of 60 Hz, the TEM₀₀ mode of laser beam with pulse width of 60 ns was obtained.     

Thermal diffusion in binary mixtures containing molecular gases II: mixtures of N2 with He,Ne, Ar,and Kr and of CO2 with He and Ar

Expressions developed for the thermal diffusion factor, αT, for binary mixtures containing molecular species have been tested for six different atom-molecule interactions. Specifically, the interactions between N₂ and He, Ne, Ar and Kr, plus the interactions between CO₂ and He, Ar, have been examined, in each case using at least two competing modern potential energy surfaces. Detailed expressions in both the ‘total-energy-flux’ and the ‘two-flux’ representations have been developed, and the importance of the anisotropic components of the intermolecular potential energy surfaces in determining the thermal diffusion factor for such mixtures has been determined.     

Numerical solution of Boltzmann tranport equation for TEA CO2 laser having nitrogen-lean gas mixtures to predict laser characteristics and gas lifetime

Selective laser isotope separation by TEA CO₂ laser often needs short tail-free pulses. Using laser mixtures having very little nitrogen almost tail free laser pulses can be generated. The laser pulse characteristics and its gas lifetime is an important issue for long-term laser operation. Boltzmann transport equation is therefore solved numerically for TEA CO₂ laser gas mixtures having very little nitrogen to predict electron energy distribution function (EEDF). The distribution function is used to calculate various excitation and dissociation rate of CO₂ to predict laser pulse characteristics and laser gas lifetime, respectively.Laser rate equations have been solved with the calculated excitation rates for numerically evaluated discharge current and voltage profiles to calculate laser pulse shape. The calculated laser pulse shape and duration are in good agreement with the measured laser characteristics. The gas lifetime is estimated by integrating the equation governing the dissociation of CO₂. An experimental study of gas lifetime was carried out using quadrapole mass analyzer for such mixtures to estimate the O₂ being produced due to dissociation of CO₂ in the pulse discharge. The theoretically calculated O₂ concentration in the laser gas mixture matches with experimentally observed value. In the present TEA CO₂ laser system, for stable discharge the O₂ concentration should be below 0.2%.     

Hydrogen analysis in metal samples by selective detection method utilizing TEA CO2 laser-induced He gas plasma

When a Transversely Excited Atmospheric (TEA) CO₂ laser (energy of 1.5 J, pulse duration of 200 ns) was focused on a metal sample surface containing hydrogen (H) in He gas at 1 atm, a strong helium gas plasma was produced and only H atoms came out of the sample. The H atoms then moved into the helium gas plasma to be excited through meta-stable helium atoms. Using this technique, an excellent linear calibration curve with zero intercept was made using zircalloy-2 samples containing H (100–600 ppm), where the compensation method was made using an emission intensity of O I 777.1 nm in order to subtract the H emission intensity coming from unwanted H₂O. It should be emphasized that this technique has a possibility to realize highly sensitive analysis of H with a detection limit of less than 1 ppm because of its selective detection.     

High repetition rate TEA CO_2 laser with randomly coded wavelength selection

High repetition rate transversely exited atmospheric pressure (TEA) CO2 laser with randomly coded wavelength selection is suggested. The laser wavelength is tuned by a Fabry-Perot (F-P) etalon of low fineness, whose space interval is controlled by a piezoelectric transducer (PZT). A digital controlled programmable voltage source is introduced to vary the voltage applied on PZT so as to swiftly shift the laser output wavelength pulse by pulse. Detailed theoretical analysis is carried out by six-temperature mode rate equations.     

High nuclear polarization in3He and3He-4He gas mixtures by optical pumping with a laser diode

New diode lasers delivering 50 mW output power at 1083 nm are shown to be efficient sources for optical pumping of helium. They can polarize nuclei in a³He gas up toM = 50% over the pressure range 0.4–1.6 torr. Larger nuclear polarizationsM of³He nuclei, of order 80%, can be obtained in³He-⁴He mixtures when the laser frequency is tuned to a⁴He line. A standard optical measurement of nuclear polarizationM has been extended to the case of³He-⁴He mixtures. The effect of various parameters on the steady-state polarizationM and on the pumping timeT _p is discussed.Laboratoire associé au Centre National de la Recherche Scientifique et à l'Université P. M. Curie     

Coupling coefficient for TEA CO2 laser propulsion with variable pulse repetition rate

Because pulse repetition rate affected directly the momentum coupling coefficient of transversely excited atmospheric (TEA) CO2 laser propulsion, a double pulse trigger, controlling high voltage switch of laser excitation circuit, was designed. The pulse interval ranged between 5 and 100 ms. The momentum coupling coefficient for air-breathing mode laser propulsion was studied experimentally. It was found that the momentum coupling coefficient decreased with the pulse repetition rate increasing.     

TEA CO2激光器预电离结构电极系统的电场研究

 高功率气体激光器的非对称复杂电极系统中,电极参数的变化以及预电离结构的引入将会使所设计的均匀电场发生具体的改变。采用高精度有限元方法,对这类复杂电极系统进行建模并且计算其电场分布,根据分析结果更合理地指导激光器设计。对一种典型的非对称复杂电极系统TEA CO₂激光器,应用该方法并结合了预电离过程,研究了引入预电离器导体和变化电极形状对电极表面的电场强度起伏和放电空间的均匀电场面积产生的影响。结果表明:通过这种预先模拟,合理选择电极构型参数和预电离结构安装位置,可以产生性质较好的均匀电场以及效率较高的激光输出。