飞秒激光与金膜作用的脉冲累积效应

采用1kHz飞秒激光（脉宽148fs,中心波长775nm）对石英衬底的金膜的烧蚀过程进行了研究．单脉冲与多脉冲的烧蚀阈值可以通过烧蚀点的直径平方与所用的激光能流的关系曲线获得．通过累积能流和烧蚀脉冲数的关系,可以得到金膜的脉冲累积因子．采用飞秒激光加工材料的一些特点可以合理解释单脉冲阈值附近获得的一些实验现象．     

重频脉冲激光辐照光学材料特性的研究进展

综述了重复频率脉冲激光辐照下光学材料特性的研究进展,重点介绍了重频激光辐照下光学材料损伤的规律,发现缺陷造成的亚损伤状态是诱导材料重频损伤的关键。详细阐述了热吸收性杂质模型、化学键断裂模型、色心模型的亚损伤机理,同时介绍了重频工作模式下激光增益介质和倍频晶体的材料特性,展望了重频激光辐照光学材料特性研究的发展和前景。     

片状石墨增强树脂基复合材料的耐激光烧蚀性能研究

采用刷涂的方法制备了一种新型的片状石墨增强钡酚醛树脂基复合材料, 并采用重频激光辐照的方法, 对其耐烧蚀性能进行了研究. 研究结果表明: 片状石墨增强钡酚醛树脂基复合材料在平均功率密度为1700 J/cm²的重频激光辐照下的热烧蚀率为32.8 μg/J, 耐激光烧蚀性能明显高于碳纤维增强的钡酚醛树脂基复合材料和钡酚醛树脂; 片状石墨增强钡酚醛树脂基复合材料中的片状石墨呈近平行的层状分布方式, 在激光辐照过程中能对入射激光起到平面反射作用, 从而有效地降低激光辐照的能量沉积; 片状石墨的片型对复合材料的耐烧蚀性能有影响, φ0.5 mm的片状石墨增强的复合材料的耐激光烧蚀性能最好.     

飞秒激光烧蚀MgAl2O4透明陶瓷的实验研究

实验研究了800nm飞秒激光与MgAl2O4透明陶瓷的相互作用，得到其在单脉冲、多脉冲情况下的损伤阈值和损伤面积，用CCD成像技术和扫描电镜观察了烧蚀点的形貌特征，用显微红外光谱仪测试了烧蚀区域的透过光谱．结果表明；单脉冲烧蚀条件下，烧蚀面积与脉冲能量近似为线性关系，而在多脉冲烧蚀条件下，烧蚀面积随着脉冲数量的增加呈近似波尔兹曼（Boltzmann）增大；当激光功率接近损伤阈值时，烧蚀后的区域在波数为2500-7000cm^-1范围内的红外透过率由82％提高到86％，当激光功率超过损伤阈值后，透过率降低20％左右．     

毫秒激光致光学薄膜损伤阈值的测试与分析

根据ISQ-11254分别测量了脉宽1 ms,波长1 064 nm激光作用下TiO2/SiO2高反膜、增透膜的损伤阈值,结合高分辨率CCD和光学显微镜观测了损伤形貌,分析了毫秒量级激光损伤光学薄膜的损伤机理.结果表明:脉宽1 ms激光作用下TiO2/SiO2增透膜的损伤阈值为高反膜的2.4倍,损伤区域为若干分离的损伤点...     

紫外激光烧蚀铜诱导电子辐射的研究

通过时间分辨技术对XeCl紫外激光烧蚀金属Cu过程中收集板上电荷的时间分辨测量,获取收集板电压信号的时间分辨,分析了激光烧蚀过程中电子与离子到达收集板的特征.结果表明,电子首先从靶面出射,离子紧随其后.收集板上的正、负电压信号分别由激光烧蚀金属Cu产生离子和电子发射而引起,高能电子对环境气体具有碰撞电离的作用.连续辐射的产生与持续时间和收集板上接收电子的负电压信号相对应.结合连续辐射强度的空间分布,对电子辐射的机理进行了探讨.认为电子辐射主要为韧致辐射,韧致辐射来源于近靶处高能电子与等离子体中的粒子相互作用,它是产生连续辐射的主要成因.     

半导体可饱和吸收镜的光损伤阈值测量

半导体可饱和吸收镜(SESAM)在飞秒脉冲激光器锁模中，是一种非常有潜力的锁模启动器．其损伤闽值的高低与连续锁模阈值比较相近，极易损伤，因而研究在飞秒激光作用下SESAM的损伤阈值很有必要．利用飞秒激光分别对单晶硅、自然生长SESAM及腐蚀后SESAM在50fs、200fs和400fs脉宽下进行了表面烧蚀研究，并且保证每次烧蚀的激光脉；中个数为50个．结果发现单晶硅和自然生长SESAM的损伤阈值要高于腐蚀乓SESAM，随脉宽的增加而逐渐增大；而腐蚀后SESAM的损伤阈值却随脉宽的增加而逐渐减小．     

碳纤维增强环氧树脂复合材料在切向气流和激光作用下的损伤

实验研究了靶板表面有0.4 Mach(1 Mach=340 m/s)切向空气气流、0.4 Mach切向氮气气流和无气流时,976 nm连续激光对碳纤维增强E-51环氧树脂复合材料的辐照效应,得到了该材料在不同功率密度下的烧蚀规律.实验结果表明:当样品发生剧烈热分解时,随热分解气体流出边界的固体颗粒对入射激光有屏蔽作用;切向气流一方面可以减弱这种屏蔽作用,有利于辐照区的烧蚀,另一方面对样品有冷却作用,不利于烧蚀;相比于氮气流,空气流有助于产物的燃烧,对下游附近区域产生明显的加热作用;切向空气气流的加载会明显提高扩散到样品表面的氧气浓度,导致碳纤维发生氧化烧蚀;三种气流状态下,当入射激光功率密度在100～800W/cm2范围内,随着功率密度的增大,激光能量的利用效率逐渐降低.     

超短脉冲激光烧蚀熔融硅的理论模型

在Fokker_P1anck方程的基础上,对超短脉冲激光烧蚀熔融硅的机理进行分析研究,建立了雪崩电离、多光子吸收电离导致的熔融硅烧蚀机理的数学模型.其计算得出的激光能量密度和临界烧蚀阀值与实验结果很好的吻合,定量解释了超短脉冲激光对熔融硅烧蚀损伤微观过程的影响.     

碳纤维增强环氧树脂复合材料在切向气流和激光作用下的损伤

实验研究了靶板表面有0.4 Mach(1 Mach=340 m/s)切向空气气流、 0.4 Mach切向氮气气流和无气流时, 976 nm连续激光对碳纤维增强E-51环氧树脂复合材料的辐照效应, 得到了该材料在不同功率密度下的烧蚀规律。实验结果表明: 当样品发生剧烈热分解时, 随热分解气体流出边界的固体颗粒对入射激光有屏蔽作用; 切向气流一方面可以减弱这种屏蔽作用, 有利于辐照区的烧蚀, 另一方面对样品有冷却作用, 不利于烧蚀; 相比于氮气流, 空气流有助于产物的燃烧, 对下游附近区域产生明显的加热作用; 切向空气气流的加载会明显提高扩散到样品表面的氧气浓度, 导致碳纤维发生氧化烧蚀; 三种气流状态下, 当入射激光功率密度在100～800 W/cm²范围内, 随着功率密度的增大, 激光能量的利用效率逐渐降低。     

一种基于光拍频的连续激光调制光谱测量方法

针对F-P干涉仪分析连续激光调制光谱的局限性,本文提出了一种基于光拍频的连续激光调制光谱的测量方法,该方法可实现调制频率低达千赫兹的连续激光调制光谱的测量.本方法以光电转换理论为基础,利用频谱分析仪测得参考光与连续调制光谱的拍频信号,然后通过相应的数学计算得到连续调制光谱的各个光频的相对电场强度,从而实现连续调制光谱的分析.本文在理论建模与分析的基础上,利用该方法对半导体激光器出射激光经电光调制器调制产生的调制光谱进行了测量,测量结果与F-P干涉仪测量结果一致,验证了该方法的可行性.     

Neuronal growth cones respond to laser-induced axonal damage

Although it is well known that damage to neurons results in release of substances that inhibit axonal growth, release of chemical signals from damaged axons that attract axon growth cones has not been observed. In this study, a 532 nm 12 ns laser was focused to a diffraction-limited spot to produce site-specific damage to single goldfish axons in vitro. The axons underwent a localized decrease in thickness (‘thinning’) within seconds. Analysis by fluorescence and transmission electron microscopy indicated that there was no gross rupture of the cell membrane. Mitochondrial transport along the axonal cytoskeleton immediately stopped at the damage site, but recovered over several minutes. Within seconds of damage nearby growth cones extended filopodia towards the injury and were often observed to contact the damaged site. Turning of the growth cone towards the injured axon also was observed. Repair of the laser-induced damage was evidenced by recovery of the axon thickness as well as restoration of mitochondrial movement. We describe a new process of growth cone response to damaged axons. This has been possible through the interface of optics (laser subcellular surgery), fluorescence and electron microscopy, and a goldfish retinal ganglion cell culture model.     

冲击损伤对C/C复合材料烧蚀性能的影响

利用Split Hopkinson Pressure Bar(SHPB)装置, 对炭化铪含量为2wt％的C/C复合材料进行了载荷峰值为137MPa的动态冲击损伤, 采用氧乙炔烧蚀装置研究了冲击损伤对C/C复合材料烧蚀性能的影响, 并结合扫描电镜讨论了冲击损伤对样品烧蚀机理的影响. 研究结果表明: 与未受冲击的C/C复合材料相比, 冲击损伤后, 复合材料的质量烧蚀率增加了40％, 线烧蚀率增加了118％.     

Induced heating by nonlinear absorption in LiNbO3-type crystals under continuous-wave laser irradiation

We investigate light-induced heating by nonlinear absorption in LiNbO₃-type crystals under continuous-wave (CW) laser irradiation. The heat source is one-photon absorption by long-lived excited states created by two-photon absorption. The accumulated effect of excited states, which act as light absorbers, is significant for a CW laser. Light-induced heating causes catastrophic CW laser breakdown in LiNbO₃-type crystals in which the band-gap energy is less than twice the photon energy and in which long-lived excited states, like polarons, can exist. For LiNbO₃, the threshold intensity for catastrophic breakdown is estimated to be in the order of MW/cm².     

Direct-write patterning of indium-tin-oxide film by high pulse repetition frequency femtosecond laser ablation

Ablation of indium oxide doped with tin oxide (ITO) from glass substrates is described. Laser pulse energy and focus spot size were varied in single-pulse, single-spot ablation tests and for ablation of linear features with scanned multiple pulses. The single-pulse ablation threshold of ITO was smaller than that of the glass substrate so the entire thickness of ITO could be removed in a single pulse or with overlying multiple pulses without the possibility of substrate ablation. Linear features could be created at much higher scanning speeds using a high repetition frequency (100 kHz) Yb fiber amplified laser as compared to a lower repetition frequency (2 kHz) laser. An analysis showed that incubation effects lowered ITO ablation thresholds when pulse frequency was high relative to scanning speed, contributing to large feasible scanning speeds for high pulse frequency lasers.     

计量型激光椭偏仪初始入射角校准方法的研究

为保证计量型激光椭偏仪测量结果的准确性,研究了一种初始入射角校准方法,通过线性位移台带动CCD相机进行一维运动,其运动轴作为空间线性辅助参考量,实现了椭偏仪的入射激光光轴与自准直仪光轴的90°校准。结果表明:采用该方法校准计量型激光椭偏仪的初始入射角,光轴俯仰角偏差＜0.05°,偏摆角偏差＜0.09°;校准后,对标称值为102.10nm的Si上SiO₂膜厚标准片进行测量,示值误差＜0.4nm,提升了计量型激光椭偏仪测量校准服务的准确性。     

基于环形激光的深孔内膛形貌检测系统研究

提出了一种基于环形激光的深孔内膛检测系统,该系统主要由环形激光发生器、反射锥镜、CCD相机以及驱动装置等组成。通过对环形激光器投射在被测身管内膛上的环形光斑进行成像和分析计算,可对身管内膛的一个截面形廓进行检测,并在驱动装置的驱动下,实现对深孔内膛形貌的三维检测。     

A Novel Strategy For Monitoring Laser Thermal Therapy Based on Changes in Optothermal Properties of Heated Tissues

Laser thermal therapy uses near-infrared optical energy to heat and thereby treat diseased tissues such as solid tumors. A method to monitor the progress of laser thermal therapy by detecting temperature-induced changes in optical propagation has been developed. The advantage of a point optical monitoring strategy over a conventional point temperature monitoring approach is that optical intensity measurements are indicative of a larger sampling volume of optothermal events. In porcine kidney in vivo, the optical intensity at 5 mm from a laser-coupled heating fiber decreased by 49\% after 2.5 min of heating at 3 W. In bovine tissue ex vivo, the optical intensity at 8 mm from the heating fiber decreased by 62--83 % during laser irradiation at 5 W. This substantial decrease in optical penetration is consistent with increased optical scattering by thermally damaged tissue (i.e., kidney and liver) around the heating fiber. This damage was not detected by a temperature sensor placed at the same distance from the \vadjust{\pagebreak}heating\break fiber in kidney or liver. Furthermore, in the porcine kidney experiment, smoke production occurred, which is normally concomitant with high-temperature tissue charring around the heating fiber. This was observed as a complete loss in optical intensity but was not detectable in the temperature data. The measurements in this work indicate that point optical intensity may have a greater sensitivity to important optothermal events than do point temperature measurements for monitoring laser heating in tissuesPaper presented at the Fifteenth Symposium on Thermophysical Properties, June 22--27, 2003, Boulder, Colorado, U.S.A.     

Plate-shaped Yb:LuPO4 crystal for efficient CW and passively Q-switched microchip lasers

It is demonstrated that plate-shaped crystals of Yb:LuPO₄, which are grown from spontaneous nucleation by high-temperature solution method, can be utilized to make microchip lasers operating in continuous-wave (CW) or passively Q-switched mode. Efficient operation of such a microchip laser, which is built with a 0.3 mm thick crystal plate in a 2 mm long plane-parallel cavity, is realized at room temperature. With 2.37 W of pump power absorbed, 1.45 W of CW output power is generated with a slope efficiency of 73%. When passively Q-switched with a Cr⁴⁺:YAG crystal plate as saturable absorber, the laser produces a maximum pulsed output power of 0.53 W at 1013.3 nm, at a pulse repetition rate of 23.8 kHz, the resulting pulse energy, duration, and peak power are 22.3 μJ, 4.0 ns, and 5.6 kW, respectively.