A study of laser cutting engineering ceramics

A mechanical chopper Q-switched CO₂ pulse laser with high peak power, short pulse duration, high pulse repetition rate and moderate average power is developed. Using this laser, a multi-pass cutting process with high cutting speed is proposed for cutting hard and brittle materials such as engineering ceramics. Crack-free and fine cut is obtained in cutting Si₃N₄ ceramics. Moreover, the formation and elimination of the cracks are qualitatively analyzed in the paper.     

激光分离卵磷脂混合物的实验研究

对于沸点相近并且分子自由程相差不大的物质,常规分离方法难以实现有效的分离,激光分离有效地弥补了常规分离方法的不足.用脉冲CO2激光器和连续CO2激光器对大豆卵磷脂混合物进行了激光分离实验,用高效液相色谱对激光辐照前后的样品进行了分析.经192.31 W/cm2的脉冲CO2激光辐照,卵磷脂的质量分数相对提高了26.7%,...     

Inert gas cutting of titanium sheet with pulsed mode CO2 laser

The present work aimed at studying the dynamic behavior of melt ejection in laser cutting of 1 mm thick titanium sheet and to obtain dross-free cuts with minimum heat affected zone (HAZ). CO₂ laser cutting of titanium sheet was carried out with continuous wave (CW) and pulsed mode laser operation with different shear gases namely argon, helium and nitrogen. Laser cutting with high frequency and low-duty cycle pulse mode operation produced dross-free cuts with no noticeable HAZ. Helium, because of its high heat convection and ability to generate high shear stress, produced laser-cuts with narrow HAZ and low dross, as compared to those produced with argon as the shear gas. Microscopic features of laser cut surfaces were analyzed and correlated with dynamic mechanism involved in laser cutting process. Process parameters for laser piercing, required for the initiation of fusion cut within the sheet, were also studied. Laser piercing requires either CW or high-duty cycle (>80%) pulse mode operation.     

Infra-red radiation focusators

This paper presents the results of investigations in the field of diffractive or ‘binary’ computer-generated optics for the infra-red region of the spectrum. The problem of a CO₂-laser beam focusing into a complicated focal domain is considered in detail. Special ray-tracing methods are elaborated to calculate the new analytic functions of diffractive optical elements, called focusators. The development of IR focusators into a ring, uniform planar spots, segments of a straight line, and other focal domains for the CO₂ lasers powered from several watts up to 3 kW is reported. Reflective-type focusators are manufactured by a specific microrelief technology that has some features in common with normal microelectronic technology. Experimental results for focused-beam interaction with rubber, wood, fabric, and plastics are presented for the case of a 30-W laser. Effective laser heat-hardening of steel is achieved by 3-kW CO₂ laser by means of a computer-generated reflective focusator.     

Photo-operated two-photon absorption effects in the GeSe2–Ga2S3–PbI2 glasses

The possibility to operate the two-photon absorption (TPA) of newly synthesized GeSe₂–Ga₂S₃–PbI₂ glasses using the CO laser beam (λ=5.5 μm) as a photoinducing one has been demonstrated. As the fundamental laser beam we have used the illumination of 10.6 μm passively modulated 0.5 ns CO₂ laser with a rate repetition of about 10 Hz. We have established that the maximal photoinduced TPA is observed for the 8% doped samples (up to 14 cm/GW), which is achieved at a pump CO laser pump power density equal to about 0.6 GW/cm². The undoped PbI₂ samples show the TPA maximum at a pump power density of about 0.2 cm/GW. The minimal TPA values were observed for the samples with 5% of PbI₂. The obtained results show that these materials can be used as effective optically operated optical limiters.     

Operation of an unstable resonator TE CO2 laser with large electrode spacing using additives

A study of a pulsed transversely excited (TE) CO₂ laser using an unstable resonator configuration is reported. It is shown that a large aperture (4.75 cm) wire-triggered device can successfully operate at pressures of up to 650 torr with undoped gas mixtures whose molecular gas concentration exceeds 35%. These results are utilised for a comparative study of the influence of an organic additive on the performance of the system. It is observed that the addition of traces of tri-n-propylamine leads to significant improvements of the laser output characteristics even under conditions where a glow discharge could be obtained without the additive. With the doped TE CO₂ laser employed using a relatively low magnification unstable resonator (M = 1.45) near diffraction-limited performance has been achieved and a peak radiance of 4.5 × 10¹³ W cm⁻² sr⁻¹ has been obtained with a peak power of 65 MW.     

Spectroscopy system based on a single quantum cascade laser for simultaneous detection of CO and CO_2

A quantum cascade laser(QCL) based system for simultaneous detection of CO and CO_2 is developed.The QCL can scan over two neighboring CO(2055.40 cm~(-1)) and CO_2(2055.16 cm~(-1)) lines with a single current scan.The wavelength modulation spectroscopy( f = 20 k Hz) is utilized to enhance the signal-to-noise ratio.A white cell with an effective optical path length of 74 m is used.The calibration of the sensor is performed and minimum detection limits of 1.3 ppb(1 × 10~(-9))for CO and 0.44 ppm(1 × 10~(-6)) for CO_2 are achieved.     

2.0 μm处CO2高温谱线参数测量研究

研究高温下待测气体的谱线属性, 如谱线强度、自加宽系数、空气加宽系数、温度系数等, 为高温环境中可调谐半导体激光吸收光谱技术反演温度、浓度、速度及其场分布提高精度和可靠性起着十分重要的作用. HITEMP数据库中的数据基本上是理论计算结果, 与实际情况存在相当的误差. 为了获得所选2.0 μm处的可用于燃烧诊断的CO₂谱线参数, 本文采用半导体激光器作为光源, 结合实验室的高温测量系统, 记录了700–1300 K温度范围内所选谱线的高温吸收光谱, 获得了各谱线在相应温度下的谱线强度、自展宽系数及温度系数等谱线参数. 测量得到CO₂的5006.978 cm^-1和5007.7874 cm^-1谱线强度与理论计算值相对误差小于11%; 获得了现有数据库缺少的温度系数和高温下自展宽系数数据. 所有各项参数对以后将要进行的燃烧诊断中的CO₂浓度检测有很大帮助. 关键词： 可调谐半导体激光吸收光谱 高温光谱 自展宽系数 温度系数     

Er3+,Yb3+共掺杂SrTiO3超细粉末的可见上转换发光

钛酸锶(SrTiO₃)具有高介电常数、良好的绝缘性质、优良的物理化学稳定性和在可见光范围内的优异的透明度等优点,是一种重要的无机功能材料。近年来,Al³⁺,Ga³⁺等离子共掺杂的SrTiO₃:Pr³⁺做为一种优异的红色场发射显示(FED)荧光粉引起了人们的兴趣。另外,SrTiO₃具有相对较小的声子频率,因而它可以作为一种有利于上转换发光的基质材料。以NaCl为助熔剂制备了Er³⁺,Yb³⁺共掺杂的SrTiO₃超细粉末。在980nm激发下,样品发出很强的来自于Er³⁺离子的²H_11/2→⁴I_15/2,⁴S_3/2→⁴I_15/2(绿光)和⁴F_9/2→⁴I_15/2(红光)跃迁的上转换发光。Yb³⁺离子的共掺杂对Er³⁺离子的上转换发光起明显的增强作用。研究了上转换发光强度与稀土离子浓度以及激发光强度之间的依赖关系,表明在Er³⁺单掺杂和Er³⁺,Yb³⁺共掺杂的样品中,绿光和红光都是被双光子激发过程激发的。还对上转换发光的机理做了初步分析。     

Efficient doubling and CW difference frequency mixing in the infrared using the chalcopyrite CdGeAs2

We have obtained fifteen percent average internal power conversion efficiency for second harmonic generation in CdGeAs₂ of radiation from a TEA CO₂ laser operating at 10.6 μm. This is the highest reported doubling efficiency for a CO₂ laser. We have also observed cw difference frequency mixing in CdGeAs₂ at wavelengths between 11.4 and 16.8 μm using grating-tuned CO and CO₂ lasers. The CdGeAs₂ crystals are significantly improved in size and optical quality over those previously available.     

Cold-cathode, glow-discharge, electron-beam gun pumped short pulse CO2 lasers

A pulsed cold-cathode glow-discharge electron beam gun emitting an electron-beam of 150 keV energy and 45 cm² cross-sectional area has been used to pump a short pulse CO₂ laser. A fast discharge capacitor bank was used to help make the design simpler than that employed in liquid coaxial lines. The system developed is capable of producing a CO₂ laser pulse of 1 J for about 200 ns duration.     

太阳光泵浦固体激光阈值的理论分析

为了选择适合太阳光泵浦的激光材料,本文从四能级速率方程出发,综合考虑了太阳辐射带状光谱特性和激光材料对泵浦光吸收能力,建立了太阳光泵浦固体激光理论模型。利用该模型推导得到了单束光侧面泵浦和椭球腔侧面泵浦方式下的泵浦阈值表达式,并结合Nd~3+∶YAG、Nd~3+∶glass、Nd~3+∶Cr~3+∶GSGG(Nd~3+∶Cr~3+∶Gd_3Sc_2Ga_3O_12)、Cr~3+∶BeAl_2O_4和Cr~3+∶Nd~3+∶YAG等激光材料的光谱参数,计算了这些材料的泵浦阈值光强。结果表明:在单束光侧面泵浦和椭球腔侧面泵浦方式下,Nd~3+∶YAG的泵浦阈值光强分别为448个太阳常数和224个太阳常数,是比较适合用太阳光泵浦的激光材料。由于椭球腔的特殊结构,采用椭球腔侧面泵浦激光介质,阈值光强比较低。分析了泵浦阈值光强与材料直径的关系。该模型可用于从现有的激光材料中筛选出在太阳光泵浦下最易输出激光的工作物质。     

Lu_(2)O_(3)∶Er^(3+)/Yb^(3+)荧光材料的上转换发光及其温度传感特性EI北大核心CSCD

采用CO_(2)激光区熔法制备了Lu_(2)O_(3)∶0.5%Er^(3+)/x%Yb^(3+)(x=1,3,5)上转换荧光材料。X射线衍射结果表明,所制备的Lu_(2)O_(3)∶Er^(3+)/Yb^(3+)荧光材料具有纯Lu_(2)O_(3)晶相。在980 nm激光激发下,样品发出明亮的上转换荧光。光谱测试结果表明,样品上转换荧光强度和荧光中绿光与红光比例随Yb^(3+)离子浓度改变,当Er^(3+)和Yb^(3+)离子浓度分别为0.5%和3%时,样品上转换荧光强度最强。通过荧光强度比(FIR)技术研究了样品Lu_(2)O_(3)∶0.5%Er^(3+)/3%Yb^(3+)在298~873 K温度范围内上转换荧光温度传感特性,在532.8 K时最大绝对灵敏度为0.0060 K^(-1),在298 K时最大相对灵敏度为0.0090 K^(-1)。结果表明,Lu_(2)O_(3)∶Er^(3+)/Yb^(3+)荧光材料非常适合用于宽温度范围荧光温度传感。     

A method to determine the parameters of laser iron and steel cutting

A simple empirical method to describe the parameters of laser iron and steel cutting, with a high quality of kerf, is given. The experiments were conducted with a 500 W cw CO₂ laser, Everlase 525, in laboratory conditions with energies in the range 150–580 W and were used as a base. They mainly agreed with the data from Refs 3 and 4.     

Beam profile monitor for pulsed CO2-laser

Commercial beam profile monitors for pulsed CO₂ lasers (10.6 μm wavelength) are expensive and suffer from a low damage threshold. To overcome these problems, a robust detector with a high damage threshold was developed. The detector is made of a special type of graphite which is evaporated during the interaction with the laser beam. A plasma is formed which radiates visible light. Using a conventional fast shutter imaging system, this plasma light directly shows the spatial intensity distribution of the laser beam. The detector works in the power range of 10⁵-10⁷ W/cm²      

载体结构对固态胺吸收CO2性能的影响

利用六种孔结构不同的商业无定形硅胶制备了不同四乙烯五胺（TEPA）担载量的固态胺吸收剂。吸收剂的微观结构通过BET和SEM测试;并在TGA反应器中,考察固态胺在30～80℃,CO2体积分数为1%～100%范围内的吸收性能。实验表明,固态胺吸收CO₂性能与温度、CO₂浓度以及载体结构有密切的联系。固态胺适合在低温（30～60℃）低CO₂浓度下（约10%）进行CO₂分离。载体结构通过影响最优担载量,从而影响固态胺吸收性能,孔容和孔径分别在1.211 cm³/g和13 nm附近的载体在担载量为45%时拥有最好的吸收能力（2.87 mmol/g）。     

Development of a high power gas transport CO2 laser with with cylindrical geometry

The aim of this work is to report the achievement of a light weight, compact, high power CO₂ laser which can be used in industry. The construction and operation of a CO₂ gas transport laser with cylindrical geometry and two parallel electrical discharges are presented. Using a 600 mm diameter, 1400 mm length, 250 kg laser head, we have obtained more than 1.6 kW laser power with 2% stability and 2 mrad full angle divergence. For comparison the results are presented for one electrical discharge laser.     

Output couplers of ultra-transparent KCl and NaCl in a pulsed CO2 laser

Uncoated plane parallel windows made from ultra-transparent KCl and NaCl crystals, which were grown by ‘injecting the reactive atmosphere’ (IRA) technique, have been tested as output windows in a high-power, high-repetition TEA CO₂ laser, in various resonator configurations. Output power densities per pulse of 2 to 6 MW cm^-2, which are 40% to 60% less than with 50% reflective coated ZnSe, have normally been obtained. The laser performances did not change after one year of operation and more than 10⁷ pulses per window. No laser damage has been observed.     

Beam quality of a high-power CO2 laser MOPA system

In this paper, the effects of amplification of diffraction-limited pulsed CO₂ laser radiation over several meters of amplification length on beam quality and pointing stability are documented. Millijoule pulses are amplified up to 3 J. Generation and amplification of the 10 μm wavelength pulses were performed in the discharge volume of an e-beam sustained CO₂ laser. Beam quality is measured according to the ISO/DIS 11146 standard in terms of the beam quality factor M². Fluence distributions were recorded with a beam analysing system of 100 μm spatial resolution. M² parameter values ranged up to 1.55 for amplified pulse energies of 3 J. The necessity of beam-quality restoring techniques is inferred for the multijoule pulse energy regime.     

High adsorption and separation performance ofCO2 over N2 in azo-based (N=N) pillar[6]arene supramolecular organic frameworks

Azo-based pillar[6]arene supramolecular organic frameworks are reported for CO₂ and N₂ adsorption and separation by density functional theory and grand canonical Monte-Carlo simulation. Azo-based pillar[6]arene provides suitable environment for CO₂ adsorption and selectivity. The adsorption and selectivity results show that introducing azo groups can effectively improve CO₂ adsorption and selectivity over N₂, and both CO₂ adsorption and CO₂ selectivity over N₂ follow the sequence pillar[6]arene_N4 > pillar[6]arene_N2 > pillar[6]arene. Pillar[6]arene_N4 exhibits CO₂ adsorption capacity of ～ 1.36 mmol/g, and superior selectivity of CO₂ over N₂ of ～ 116.75 with equal molar fraction at 1 bar (1 bar=10⁵ Pa) and 298 K. Interaction analysis confirms that both the Coulomb and van der Waals interactions between CO₂ with pillar[6]arene frameworks are greater than that of N₂. The stronger affinity of CO₂ with pillar[6]arene_N4 than other structures and the larger isosteric heat differences between CO₂ and N₂ rendered pillar[6]arene_N4 to present the high CO₂ adsorption capacity and high CO₂ selectivity over N₂. Our results highlight the potential of azo-functionalization as an excellent means to improve pillar[6]arene for CO₂ capture and separation.