CO2气体激光器的激励技术及其发展趋势

本文主要介绍了CO2气体激光器的各种激励方式及其特点,分析了各自的优缺点,对其各种性能做出了对比,并指出从直流到交流、从低频到高频是CO2激光电源发展的总体过程和趋势.     

Repetitive operation of switchless transverse flow transversely excited atmosphere CO2 lasers

The enhanced preionisation efficiency of a mutually coupled parallel spark preioniser has been exploited to achieve switchless operation of a transversely excited atmosphere (TEA) CO(2) laser in the conventional transverse gas flow configuration. This made the laser more compatible to repetitive operation and the satisfactory performance of a switchless TEA CO(2) laser of ~8 cc active volume is reported here up to a maximum repetition rate of 100 Hz at a gas replenishment factor of ~2.     

旋转气流控制激光切割硅钢新技术

针对目前激光切割工艺的缺点,提出采用氧辅助激光切割以降低所需激光切割功率,通过在工件底部加设旋风除渣器,形成旋转气流控制熔渣流向以去除熔渣的激光切割硅钢新技术。采用CO2激光器,对0.5 mm厚度硅钢片进行切割试验,试验结果表明,通过旋转气流主动控制,当气流处于层流状态时,可在较低激光切割功率时获得光滑的精细切口。利用有限元法对工件底部气流状况进行数值模拟,验证了旋转气流的工作规律,能为合理控制熔渣流向提供理论依据。     

湿度和SF_6在石英增强光声光谱中对CO分子弛豫率的影响

为了研究六氟化硫(SF_6)气体分子和水汽(H_2O)对一氧化碳(CO)气体分子的弛豫率的影响,建立了一个基于石英增强光声光谱(QEPAS)技术的痕量气体传感器系统。采用1.57μm的近红外分布式反馈二极管激光器作为激励光源,并对不同SF_6和H_2O气体浓度下的CO的光声信号进行对比研究。首先用CO传感器系统探测CO与N_2的气体混合物中CO的光声信号,然后在CO与N_2气体混合物中加入不同浓度的SF_6气体,分别探测不同浓度SF_6气体下的CO光声信号强度。最后在CO与N_2的气体混合物中加入不同浓度H_2O,探测加入H_2O后的CO的光声信号强度。实验结果表明随着CO和N_2气体混合物中SF_6气体浓度的增加,CO的光声信号幅值几乎没有变化,而在混合物中加入2.5%的H_2O后,发现CO的光声信号提高了约5倍。因此,SF_6对CO气体的弛豫率没有明显的影响,然而H_2O的添加能够有效缩短CO气体的弛豫时间。     

不同波长激光对激光—MAG电弧复合焊接熔滴行为的影响

通过计算分析了金属对Nd：YAG激光和CO2激光的吸收率;以8.0mm厚高强钢板为试验材料,采用高速摄像系统观测熔滴过渡模式和等离子体形态的变化.建立脉冲MAG焊接熔滴力学模型,从熔滴受力角度分析了不同波长两种激光YAG激光和C02激光在激光—MAG焊接中对熔滴过渡形式和熔滴过渡频率的影响.结果表明,Nd：YAG激光和CO2激光输出特性存在差异,金属表面对YAG激光的吸收率约为CO2激光的3倍多;在焊接电流180A、焊接电压26V、光丝间距3mm的相同条件下,YAG激光—MAG电弧复合焊接熔滴过渡频率高于CO2激光—MAG电弧复合焊接的熔滴过渡频率,且熔滴过渡频率均随着激光功率的增加而降低,但是增加等量的激光功率,YAG激光—MAG电弧复合焊接熔滴过渡频率下降幅度更大;CO2激光—MAG电弧复合焊接过程中,熔滴的过渡形式由射滴过渡转变为颗粒过渡,在YAG激光—MAG电弧复合焊接过程中,熔滴过渡形式主要为射滴过渡.     

CO_2激光深熔焊接光致等离子体吸收及其控制

研究高功率密度 CO2 激光焊接过程中光致等离子体对入射激光的吸收以及侧吹辅助气体对等离子体控制的影响。采用准基模 CO2 激光束在 1 Cr1 8Ni9Ti不锈钢表面进行扫描焊缝 ,通过光谱检测装置检测等离子体辐射谱线强度 ,从而计算等离子体对激光的吸收系数 ;采用侧吹喷嘴分别通CO2 、N2 、Ar、He4种气体压缩等离子体。研究结果表明 ,光致等离子体对入射激光能量的吸收损失高达 2 0 % ;随着侧吹辅助气体流量的增加 ,焊缝呈现3个区间 :当气体压力低于金属蒸汽压力时 ,焊缝为“酒杯”状 ,深宽比很小 ;当辅助气体操作压力稍高于金属蒸汽压力 ,等离子体可被有效控制从而获得最佳焊缝。     

CO2激光焊接接头性能的试验分析

采用同轴和侧吹保护气体控制等离子的方法,对车身专用高强度镀锌钢板的CO2激光焊接接头的性能进行了大量的焊接试验研究,并对焊缝进行显微组织分析和相关的机械性能检测.研究激光焊接高强度镀锌钢板的工艺参数对焊接接头的抗拉强度、屈服强度和延伸率等机械性能指标的影响规律,优化了激光焊接的工艺参数.试验表明随着激光焊接过程中输入线能量的增加,焊缝区的硬度值逐渐下降,拉伸试件断裂的区域、断口韧窝大小及分布情况各不同,且焊缝的拉伸裂纹均向母材扩展,说明激光深熔焊接可以有效地避免高强度镀锌钢板焊接接头的软化.     

Compact flowing gas system for CO(2) lasers

A miniature air-actuated vacuum pump has been utilized to effect gas flow at partial atmospheric pressures for waveguide CO(2) lasers. Implications are that flowing gas laser systems can be acceptable for many applications requiring miniaturization of components.     

Laser pumping by PFN power source

The use of a pulse forming network (PEN) as a main discharge power supply was tested in a electron-beam-controlled CO(2) laser amplifier in order to improve the utility efficiency of the energy in storage capacitors. The impedance of the pumping discharge through the laser gas was controlled by the accelerating voltage of the electron beam to match the PFN line impedance. In the matched condition all of the stored energy in the PFN was transffered to the laser gas at a constant electric field strength which was optimum for laser pumping.     

千瓦级离心风机轴流CO2激光器

本文报导了使用离心风机的千瓦级轴流CO₂激光器。由于解决了油污染问题,密闭循环时间大于4小时,具有极明显的经济效益。     

Microstructure and wear resistance of CP titanium laser alloyed with a mixture of reactive gases

Laser processing is a promising technique for alloying and synthesis of wear resistant layers. In this work, commercially pure titanium was laser alloyed with various proportions of nitrogen and carbon monoxide in order to produce a composite surface layer. The following gas mixtures were selected: 100% N₂, 67% N₂ + 33% CO, 50% N₂ + 50% CO, 33% N₂ + 67% CO and 100% CO. The microstructure, roughness and composition of coated specimens were characterized. The presence of Ti(C,N,O) in the surface layer was assessed by X-ray diffraction, X-ray photoelectron spectroscopy and Auger electron spectroscopy. The abrasive wear resistance of coatings was determined and related to their surface hardness. The abrasive wear resistance of the laser alloyed coating was substantially improved compared to untreated titanium and appears to be superior when composed of Ti(C,N,O) prepared from a mixture of gases.     

A capillary absorption spectrometer for stable carbon isotope ratio (13C∕12C) analysis in very small samples

A capillary absorption spectrometer (CAS) suitable for IR laser isotope analysis of small CO(2) samples is presented. The system employs a continuous-wave (cw) quantum cascade laser to study nearly adjacent rovibrational transitions of different isotopologues of CO(2) near 2307 cm(-1) (4.34 μm). This initial CAS system can achieve relative isotopic precision of about 10 ppm (13)C, or ～1 per thousand (per mil in delta notation relative to Vienna Pee Dee Belemnite) with 20-100 picomoles of entrained sample within the hollow waveguide for CO(2) concentrations ～400-750 ppm. Isotopic analyses of such gas fills in a 1-mm ID hollow waveguide of 0.8 m overall physical path length can be carried out down to ～2 Torr. Overall (13)C∕(12)C ratios can be calibrated to ～2 per thousand accuracy with diluted CO(2) standards. A novel, low-cost method to reduce cw-fringing noise resulting from multipath distortions in the hollow waveguide is presented, which allows weak absorbance features to be studied at the few ppm level (peak-to-rms) after 1000 scans are co-added in ～10 s. The CAS is meant to work directly with converted CO(2) samples from a laser ablation-catalytic combustion micro-sampler to provide (13)C∕(12)C ratios of small biological isolates currently operating with spatial resolutions ～50 μm.     

不锈钢板的CO2激光切割工艺研究

实验用CO2激光切割厚0.8mm的1Cr18Ni9Ti不锈钢板。研究了激光功率、辅助气体类型及压力、切割速度对切割质量的影响。实验显示提高切割速度能降低切缝宽度和切口横截面的表面粗糙度;而提高激光功率和氧气压力,切缝宽度也会随之提高,切口横截面更粗糙。功率650~700W、氧气压力0.3~0.5MPa、切割速度3.5~4.5m/min时切割质量最好。另外发现功率在780~1450W,氮气压力低于0.8MPa不能得到良好的切割质量。     

AN ALL-FIBER GAS SENSING SYSTEM USING HOLLOW-CORE PHOTONIC BANDGAP FIBER AS GAS CELL

An all-fiber compact gas sensing system using a hollow-core photonic bandgap fiber (HC-PBF) as a gas cell is proposed in this paper. Compared with the present reported microstructured optical-fiber gas cells, the HC-PBF gas cell proposed here has relatively lower transmission loss and much simpler construction. The total transmission loss through the HC-PBF gas cell is demonstrated experimentally to be as low as 1.5 dB and the time taken for gas to get into the 90-cm-cell, under the free diffusion condition, is approximately 11 min. Combining the HC-PBF gas cell with a tunable fiber laser, an all-fiber gas sensing system is developed. The properties of the proposed system are demonstrated experimentally by detection of carbon monoxide (CO) and acetylene (C₂H₂). Approximately linear relationships between the system responses and the concentrations of the detected gases are experimentally demonstrated. The minimal detectable concentration of CO of 300 ppm and C₂H₂ of 5 ppm are also achieved respectively by the experiments.     

Ultrahigh vacuum chamber for Raman studies of gases adsorbed on metals

An ultrahigh vacuum chamber is described which is being used to study laser Raman spectra associated with gas adsorption on clean metal surfaces. The system enables sample temperatures from -85 degrees to 600 degrees C to be obtained, and besides surface cleaning capabilities associated with high-temperature oxidation or reduction, it incorporates an Ar(+) sputter gun for surface cleaning. Initial experiments of CO+H(2) adsorption on crystalline Ni surfaces are described and the effects of H(2) and O(2) exposure shown for the 80 cm(-1) band which results from CO+H(2) adsorption.     

声光调QCO_2激光器

为满足激光测距、环境探测、空间通讯及激光与物质相互作用机理研究等领域应用要求,研制了声光调Q CO2激光器.针对影响声光调Q CO2激光器输出的各种因素,利用调Q脉冲激光器速率方程对该激光器输出的主要技术参数进行了理论分析和计算,提出了声光调Q CO2激光器优化设计的方法,并进行了验证实验.激光器脉冲重复频率为1 Hz～50 kHz, 在1 kHz运转时获得的输出激光脉冲宽度为180 ns,峰值功率为4 062 W,与理论计算基本一致.结果证明:通过声光晶体(AO)的优选及谐振腔的合理设计,可实现小型CO2激光器的高重频、窄脉宽,高峰值功率输出,并可通过光栅选线的设计方式和TTL信号控制实现此类激光器的波长调谐和编码输出.     

高强铝合金厚板窄间隙激光焊接新工艺

针对铝合金厚板激光焊接存在的问题,提出采用窄间隙激光焊接的工艺技术路线,在分析了这种工艺方法的难点后,采用3.5 kW高光束质量扩散冷却slab CO2激光器,通过工艺方案的优化,首次成功实现了20 mm厚铝合金的窄间隙激光焊接.     

CO_2气体冷却器的性能模拟与优化计算

CO2气体冷却器的结构和换热效果对CO2跨临界制冷循环的性能影响较大,为了能设计出高效的气体冷却器,有必要对CO2气体冷却器进行性能模拟和优化研究。本文首先建立了CO2气体冷却器分布参数计算模型,对CO2制冷剂的出口温度、冷却水出口温度和换热量进行了模拟计算,并与试验测试结果进行了比较,验证了模型的可靠性。然后利用该模型对CO2气体冷却器进行了优化计算,主要分析了换热管径和管长对热重比及压降的影响。结果表明,热重比随管径的增大而下降,随管长的增加而增大。综合考虑热重比和压降两方面因素,CO2气体冷却器适合选择小管径和长管长。     

涡流分离热气体再加热的CO_2热泵系统的分析

对涡流分离热气体再加热的CO2热泵系统进行热力性能分析,并与相同运行工况下的节流降压CO2热泵系统的性能进行了对比,得出涡流分离热气体再加热的CO2热泵系统存在最优的高压压力,在最优的高压压力下,系统获得最大的制热性能系数。提高分离热气体质量比、中间压力、蒸发温度、涡流管制热效应,降低气体冷却器出口温度,涡流分离热气体再加热的CO2热泵系统的制热性能系数提高。随着热气体质量比的增加和气体冷却器出口温度的升高,涡流分离热气体再加热的CO2热泵系统最优的气体冷却器出口压力也升高。在热气体质量比仅为0.2时,涡流分离热气体再加热的CO2热泵系统相比节流降压CO2热泵系统,最佳的制热性能系数提高11%。随着热气体质量比的增加,差值会进一步增大。气体冷却器出口温度的升高,对涡流分离热气体再加热的CO2热泵系统制热性能系数的影响要小于对节流降压CO2热泵系统的制热性能系数的影响。     

采用CO2激光器进行激光雕刻工艺研究

采用CO2激光器可以对许多材料进行雕刻,效果十分理想。通过对各种材料进行CO2激光雕刻实验研究,并比较、分析雕刻效果,从而找出每种材料最佳雕刻工艺参数,形成雕刻工艺参数库,为实际应用提供技术支持,具有重要的实际意义。由于激光本身的一系列优点,该技术在工业生产中具有十分广阔的应用前景。