高重频CO_2激光损伤HgCdTe晶体的数值分析

针对CO2激光作用下HgCdTe晶体的损伤问题进行了数值分析。首先,建立了高重频CO2激光损伤Hg0.784Cd0.216Te晶体的三维热传导物理模型;然后,利用有限元方法计算了单脉冲和高重频CO2激光作用下,Hg0.784Cd0.216Te晶体的损伤阈值;最后,分析了激光重频以及辐照时间对晶体损伤阈值的影响。研究结果表明:单脉冲激光辐照下,晶体的损伤阈值为64.5 J/cm2;高重频(f>1 kHz)激光辐照下,激光重频的改变对晶体损伤阈值的影响较小,损伤阈值应由平均功率密度表征,且与辐照时间密切相关;辐照时间的增加,可以有效地减小晶体的损伤阈值,当激光辐照功率密度<1.95 kW/cm2时,不会发生晶体损伤。研究结果对高重频CO2激光在激光加工以及激光防护的应用方面具有指导意义。     

强激光对星载光电探测系统的干扰与破坏研究

建立了激光辐照星载光电探测器的数学模型,对激光干扰和破坏星载光电系统的机理进行了研究,分析了激光光束与探测器光轴的偏角对干扰和破坏的影响.以CO2激光辐照HgCdTe探测器的实例,研究了强激光对探测单元的破坏,得到其损伤阈值曲线,并从理论上证明了强激光对星载光电探测系统干扰和破坏的可行性.     

脉冲激光辐照TiO2／SiO2薄膜的热效应

用1．06μm单脉冲激光辐照TiO2／SiO2薄膜，利用得到的综合参数K来计算不同能量下单脉冲激光辐照薄膜产生的温度场和热应力场，并对计算结果进行分析，获得了温度场和热应力场在激光辐照过程中的变化过程及热应力在脉冲激光辐照薄膜过程中起主导作用。     

多脉冲激光对胶合透镜热破坏效应研究

具有一定强度的激光辐照胶合透镜时可造成透镜的破坏.建立了多脉冲激光与材料相互作用的一维非稳态温度场模型，计算了瞬态温度场分布，并对胶合透镜前表面的熔融和胶合材料的软化进行了数值模拟研究.利用频率为10Hz，脉冲宽度为200ns，峰值功率为20MW的CO₂激光对胶合透镜进行辐照实验研究.实验表明，当激光辐照时间为12s时，胶合透镜前表面发生熔融破坏；当照射时间为30s时，胶合材料发生软化并出现彩色斑纹，透镜完全破坏，理论分析与实验结果相符. 关键词： 胶合透镜 激光辐照 激光破坏     

1.06μm连续与脉冲激光对GaAs材料的联合破坏效应

 通过1.06μm连续激光和脉冲激光联合破坏GaAs材料的实验研究, 给出了GaAs材料在三种不同的连续激光功率密度辐照下, 所需脉冲激光的破坏阈值, 结果表明, 联合破坏时所需脉冲激光的破坏阈值小于单独使用脉冲激光的破坏阈值。根据轴对称二维热模型, 计算了三种情况下连续激光辐照时GaAs材料的表面温度分布曲线及表面辐照中心处温升随辐照时间的关系, 并估算了其后作用的脉冲激光对材料的温升, 对实验及计算结果进行了分析, 并着重比较了联合破坏方式和单独破坏方式的优缺点。     

1.06μm连续与脉冲激光对GaAs材料的联合破坏效应

通过1.06μm连续激光和脉冲激光联合破坏GaAs材料的实验研究, 给出了GaAs材料在三种不同的连续激光功率密度辐照下, 所需脉冲激光的破坏阈值, 结果表明, 联合破坏时所需脉冲激光的破坏阈值小于单独使用脉冲激光的破坏阈值。根据轴对称二维热模型, 计算了三种情况下连续激光辐照时GaAs材料的表面温度分布曲线及表面辐照中心处温升随辐照时间的关系, 并估算了其后作用的脉冲激光对材料的温升, 对实验及计算结果进行了分析, 并着重比较了联合破坏方式和单独破坏方式的优缺点。     

脉冲CO2激光辐照K9玻璃的热力效应分析

利用有限元法对脉冲CO2激光辐照K9玻璃样品中的温度和应力分布进行了数值分析。对半径为20mm、厚为2mm的圆盘样品的计算结果表明，K9玻璃的损伤由环向应力控制，体损伤先于面损伤产生，且光斑半径和脉冲数目对损伤闽值有较大的影响，在激光光斑半径为5mm，脉宽为10肛s的条件下K9玻璃的单脉冲CO2激光的损伤闽值为0．5J，相应的能量密度为0．637 J／cm^2。损伤闽值随光斑半径的增大而增大，随脉冲数目的增加而变小。讨论了样品半径和厚度对损伤结果的影响，结果表明样品半径在10-20mm范围内所产生的拉伸应力较小。     

La0.67Ba0.33MnO3薄膜的激光辐照效应研究

利用脉冲激光沉积技术在LaAlO3(00l)单晶衬底上制备了La0.67Ba0.33MnO3薄膜,研究了CO2激光辐照对La0.67Ba0.33MnO3薄膜的微结构和磁电性能的影响.结果表明,经激光辐照后,La0.67Ba0.33MnO3薄膜的结晶性增强,薄膜应变减小;薄膜表面形貌由"岛状"结构变为"平原"结构,且粗糙度大大降低;同时,薄膜的饱和磁化强度、铁磁居里温度、金属-绝缘态转变温度和磁电阻增大,而矫顽场和电阻率减小.根据对传统退火效应的分析和理论计算,认为激光辐照导致的表面微结构的变化以及薄膜的氧含量和均匀性的提高对La0.67Ba0.33MnO3薄膜的磁电性能的改善与优化密切相关.     

纳秒级脉冲激光诱导Zn掺杂过程中GaN/Al2O3 材料的温度分布及热形变解析分析

分析了纳秒级脉冲激光作用下GaN的激光诱导Zn的掺杂过程.利用简化的一维模型,给出一种比较直观的脉冲激光辐照下GaN/Al2O3材料温度分布的解析形式,得到了GaN材料表面温度与激光辐照时间的关系以及材料形变与深度的关系.在激光脉冲作用时,GaN材料表面的温度与辐照时间的平方根成正比.脉冲过后,材料温度分布梯度和热形变分布随深度发生变化,接近表面的温度梯度最大,热形变量也最大.而在连续脉冲作用时表面的温度呈锯齿状不断升高.     

重复脉冲激光辐照光学材料的热力效应

在建立高斯型重复脉冲激光辐照光学材料模型的基础上,得到了圆柱型光学材料的二维温度场和热应力的解析解.以K9玻璃为例,通过数值计算得到同条件下重复脉冲激光对光学材料的损伤阈值.研究表明：在高斯型重复脉冲激光辐照下,损伤阈值受到脉冲数目、宽度、重复频率以及脉冲激光光斑半径的影响,多数情况下K9玻璃会发生热应力损伤.     

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.     

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      

用于红外激光防护的高开关率VO2薄膜

采用反应离子束溅射和后退火处理技术在石英玻璃基底上制备了具有纳米粒子的二氧化钒(VO₂)薄膜. 该薄膜具有半导体-金属相变特性,在3 μm处的开关率达到76.6%。 热致相变实验结果给出了准确的最佳退火温度为465 ℃. 仿真、热致相变和光致相变实验都显示VO₂薄膜在红外波段具有很高的光学开关特性. 光电池防护实验结果显示VO₂薄膜将硅光电池的抗干扰能力提升了2.6倍, 证明了VO₂在激光防护中的适用性. 采用连续可调节系统研究得到VO₂在室温条件下的相变阈值功率密度为4.35 W/cm², 损伤阈值功率密度为404 W/cm²。 低相变阈值和高损伤阈值都进一步证明VO₂薄膜适用于激光防护系统。本实验制备的VO₂薄膜在光开关、光电存储器、智能窗等方面也具有广泛的应用价值.     

Positronium Decay in a Circular Polarized Laser Field

We calculate the lifetime of both the o-Ps and the p-Ps positronium annihilation decay Ps→γγ in the strong circular polarized laser field. We take a strategy of the factorization to separate the effects caused by the Coulomb interaction and the strong laser field interaction. It is factorized in the time direction but not in the space direction. Our results show that in the laser with long wavelength and high intensity, the lifetimes of those Ps states are dramatically increased. For CO₂ laser with 10 μm wavelength and 10¹³ W/cm² intensity, lifetime of the spin-single positronium is increased by 10⁸ times. Our result is consistent with those obtained by solving the Schödinger equation. This effect may be useful for the high harmonic generation (HHG) effects provided with the Ps [Phys. Rev. Lett. 70 (1993) 774; Phys. Rev. Lett. 93 (2004) 013601].     

快重离子辐照对MoS2热导率的影响研究

利用0.97 GeV的209Bi离子辐照二硫化钼（MoS₂）晶体,辐照注量范围为1×1010～1×1012 ions/cm2,结合原子力显微镜（AFM）观测和Raman光谱分析研究了快重离子辐照对MoS₂热导率的影响。实验结果显示,快重离子辐照在MoS₂中产生了潜径迹,较高激光功率下的Raman测试使样品局部温度升高,导致E_1/2g和A_1g峰随注量增加向低波数方向移动,且峰形展宽。引入了通过改变激光功率测量Raman光谱得到MoS₂热导率的计算方法,获得了不同辐照注量下MoS₂的热导率的定量分析结果,随注量增加,热导率不断降低,从未辐照样品的563 W/mK下降到1×1012 ions/cm2辐照时的132 W/mK。Molybdenum disulphide (MoS₂) was irradiated by 0.97 GeV 209Bi ions with the fluence of 1×1010 to 1×1012 ions/cm2. The irradiation effect on the thermal conductivity of MoS₂ was analyzed by atomic force microscope (AFM) and Raman spectroscopy. The experimental results show that hillock-like latent tracks are observed on irradiated MoS₂ by AFM. The measurement of MoS₂ by Raman spectrometer with high laser power results in the increase of local temperature of MoS₂, which cause the downshift of peaks position and broadening of E_1/2g and A_1g peak. Furthermore, according to Raman spectra measured at different laser power, thermal conductivity of MoS₂ before and after irradiation was calculated, which show that the thermal conductivity of MoS₂ decreases with increasing fluence, from 563 to 132 W/mK for pristine and 1×1012 ions/cm2 irradiated MoS₂, respectively.     

Phase transition and chemical decomposition of liquid carbon dioxide and nitrogen mixture under extreme conditions

Thermodynamic and chemical properties of liquid carbon dioxide and nitrogen(CO_(2~–)N_2) mixture under the conditions of extremely high densities and temperatures are studied by using quantum molecular dynamic(QMD) simulations based on density functional theory including dispersion corrections(DFT-D). We present equilibrium properties of liquid mixture for 112 separate density and temperature points, by selecting densities ranging from ρ = 1.80 g/cm~3 to 3.40 g/cm~3 and temperatures from T = 500 K to 8000 K. In the range of our study, the liquid CO_(2~–)N_2 mixture undergoes a continuous transition from molecular to atomic fluid state and liquid polymerization inferred from pair correlation functions(PCFs)and the distribution of various molecular components. The insulator–metal transition is demonstrated by means of the electronic density of states(DOS).     

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.     

Absolute spectral distribution of soft X-ray emission from laserproduced gold plasma

Quantitative measurement of spectral distribution of soft X-ray emission from laser produced plasmas and estimation of X-ray conversion efficiency are reported. The X-ray emission from planar gold target irradiated by an Nd:glass laser was recorded using a high resolution transmission grating spectrograph. Spectral distribution of X-ray intensity was derived using calibrated film data and a deconvolution procedure to account for contribution of higher diffraction orders. Results of conversion efficiency per unit solid angle, at a laser intensity of ~4×10¹² W/cm² (λ_L = 1.054 μm), for 10< λ <80 Å and in the water window spectral region (23< λ< 44 Å) are presented. A three-fold increase in conversion efficiency was observed for second harmonic laser irradiation (λ_L = 0.527 μm) at an intensity of 8×10¹² W/cm²     

散射光信号与石墨-二氧化硅激光辐照烧蚀阈值的关系

石墨-二氧化硅作为无机添加材料,广泛应用于各类航空航天器烧蚀涂层领域,其在高温下具有较高的反应吸热焓,在高能激光烧蚀领域具有良好的应用前景。目前,关于石墨-二氧化硅的高能激光烧蚀研究较少,尤其在高能激光烧蚀中的反应时间和烧蚀阈值难以确定。针对此问题,利用近红外探测器对激光辐照样品表面的散射光进行实时探测,并对其散射光曲线进行微分拟合处理。基于此散射光信号,结合样品烧蚀后的形态结构分析,研究了石墨-二氧化硅在不同激光功率密度下的反应时间阈值。研究结果表明:在激光输出功率密度为500 W/cm~2持续辐照10 s时,散射光拟合曲线持续升高无突变,表明未发生明显的烧蚀;当激光功率密度升高至1 000~1 500 W/cm~2时,散射光微分拟合曲线出现明显转折点,对应的反应时间阈值分别为1.5 s和0.8 s。     

H$lt;sub$gt;2$lt;/sub$gt;$lt;sup$gt;+$lt;/sup$gt;在强激光场中的解离及其量子调控的理论研究

利用非波恩-奥本海默近似的三维含时量子波包法,理论研究了氢分子离子在强激光场中的解离动力学.通过分析H₂⁺在不同的初始振动态（ν=0–9）和激光场强度下的解离核动能谱,得到了H₂⁺的光解离机理及其随激光场的变化规律.研究结果表明：当激光场的强度I₁=5.0×10¹³ W/cm²时,分子的解离来源于高振动态ν=5–9,其解离机理主要是通过键软化、键硬化和阈下解离过程.当激光场的强度I₂=1.0×10¹⁴ W/cm² 时,H₂⁺在低振动态ν=3–4上的阈上解离起主导作用,而高振动态的键软化、键硬化和阈下解离所占的比重明显地下降了.研究结果为后续的量子调控的实验研究提供了科学的理论预测和指导. 关键词： 光解离 氢分子离子 含时波包法 核动能谱