铒激光脉冲消融泌尿结石和胆结石比较研究

利用光学弱相干显微成像系统对脉冲激光消融硬生物组织后形成的凹坑二维和三维形貌进行了扫描,分析了Erbium∶YAG激光脉冲消融生物硬组织特性.结果表明：相同激光参量条件下,消融胆结石比消融泌尿结石具有更高的消融效率|消融胆结石或消融泌尿结石时,脉冲能量越大,消融效率越高|消融效率提高主要体现在凹坑表面直径更宽、高度更深、体积更大|光学弱相干显微成像技术比光学弱相干光层析成像技术测量准确度提高约一个量级,更适合于测量脉冲激光消融生物硬组织后形成的凹坑形貌.     

脉冲CO_2激光伴水喷雾的骨组织消融

评估水喷雾条件对脉冲激光辐照骨硬组织的消融速率、消融效率以及组织表面形态学变化的影响。实验样品为新鲜离体牛胫骨组织;光源为脉冲CO2激光(波长10.64μm),脉冲频率60 Hz,能量密度26.5 J/cm2,光束经关节臂传输后聚焦在组织样品表面进行垂直点状照射,光斑尺寸为400μm,辐照时间10 s。激光辐照时,水雾以45°角倾斜向组织表面喷射,喷水速率分别设置为0(无喷水),0.26,0.5,0.6,0.7和0.9 mL/s。辐照后,体式显微镜观察组织样品表面形貌变化,OCT技术测量弹坑深度,扫描电镜观察弹坑微结构变化。结果表明,水喷雾条件对脉冲CO2激光骨硬组织的消融速率,消融效率以及组织表面形态学变化具有重要影响:水喷雾不仅可以起到冷却和降低热损伤的作用,通过优化选择激光辐照参数和喷水速率,可以显著增大消融速率和消融效率,改善靶组织表面的形态结构。     

铜原子的二步三光子共振电离

本文研究了适合于共振激光消融质谱的铜原子的二步三光子共振电离过程。在较严格的条件下求解了该过程的速率方程,并分析了在脉冲激光作用下共振电离信号的探讨效率,以及影响电离效率的光通量等各种因素。本文的计算方法具有普适性,而其理论结果对于共振激光消融的实验研究具有指导意义。     

紫外激光消融有机物的理论和实验研究

本文分析了紫外准分子激光对有机材料的消融过程,用理论模型解释了每个激光脉冲对有机材料的消融量与入射激光能量密度之间的关系.对于有机玻璃.当入射激光能量密度较高时,双光子过程将起主要作用.最后讨论了消融率随有机材料吸收系数之间的关系,对吸收系数较小的材料,消融率随吸收系数改变有一个极大值.     

调Q双红外脉冲激光皮下消脂初探

人体过多的脂肪严重影响形体美和健康。为了提高消脂效率可选择高吸收系数的激光,但其不易穿透表皮和真皮到达脂肪表面进行消脂。基于消融性微小光热解效应和选择性光热解效应的基本原理,采用聚焦、调Q的2.75 mm波长中红外脉冲激光消融皮肤表皮和真皮,形成微小的通道,便于后续聚焦、调Q的2.3 mm波长红外脉冲激光能量无损地穿过通道选择性光热解脂肪组织,光热解产物通过新陈代谢排出体外,微小消融区在周围正常组织作用下快速愈合,实现消脂治疗安全性和有效性的和谐统一。该研究可为皮肤科手术治疗提供一种新方法。     

空化粉碎结石的试验研究

体外冲击波碎石术已经在临床上取得了成功的应用,但其引起的空化对组织的损伤以及如何合理利用空化来提高碎石效率还有待更细致的研究.本文利用兆赫兹频率级别的聚焦超声换能器诱发冲击波作用于结石模型材料,采用不同的声波参数包括频率、强度、占空比等进行了实验.结果表明,聚焦冲击波对结石的损伤呈凹坑状;空化在凹坑形成初期起到主导作用;采用高低频搭配的脉冲超声波可以实现对结石模型最大的损伤.     

用脉冲紫外激光预处理提高刀具的金刚石涂层的附着强度

 采用脉冲紫外激光（XeCl，308nm）表面消融预处理方法以硬质合金为衬底制备了金刚石涂层刀具。利用压痕法对涂层结合强度进行了测试，得到了最佳预处理工艺条件。采用碳化硅增强铝合金材料对制备的金刚石涂层刀具进行了实际切削性能实验。实验结果表明：脉冲紫外激光表面消融预处理方法的采用对刀具的金刚石薄膜涂层附着强度的提高有很大的帮助。     

飞秒激光微加工Au膜

飞秒激光微加工薄膜对于MEMS设备的制造是一个急需的技术。文章使用波长为775 nm的Ti: sapphire飞秒激光器(脉宽约为130 fs, 频率为1 000 Hz)研究厚度为4 μm的Au薄膜,在不同加工参数下的结构特性,发现单脉冲消融时消融直径随着脉冲能量的增大而增大。当单脉冲能量一定时,消融直径随着脉冲的个数变化不大。计算得到Au膜的单脉冲消融阈值为F_th＝0.7 J·cm-2,使用脉冲能量略大于阈值时,在薄膜上所划出的线为凸起状;当超过阈值时所得直线为凹起状。同时发现在脉冲能量一定时所得线宽随着加工速度的增加而减小;当加工速度一定时线宽随着能量的增加而增大。     

用脉冲紫外激光预处理提高刀具的金刚石涂层的附着强度

采用脉冲紫外激光（XeCl，308nm）表面消融预处理方法以硬质合金为衬底制备了金刚石涂层刀具。利用压痕法对涂层结合强度进行了测试，得到了最佳预处理工艺条件。采用碳化硅增强铝合金材料对制备的金刚石涂层刀具进行了实际切削性能实验。实验结果表明:脉冲紫外激光表面消融预处理方法的采用对刀具的金刚石薄膜涂层附着强度的提高有很大的帮助。     

脉冲激光等离子体冲击波碎石机理分析

利用自行研制的Nd:YAG激光器产生的纳秒和微秒激光脉冲,分别在水中和空气中对几种人体结石进行了粉碎实验,激光被耦合到芯径为400μm的石英光纤中,耦合效率达70%.实验研究和分析计算表明脉冲激光等离子体冲击的产生是激光碎石的主要动力,而热分解作用只是促进了等离子体的形成并不是粉碎结石的主要原因,体液冲流和周围介质对等离子体的约束加速了碎石过程,脉冲激光碎石的过程是这几个方面共同作用的结果。     

Finite element simulation of pulsed laser ablation of titanium carbide

In the present paper, a 2D finite element model based on the heat-conduction equation and on the Hertz-Knudsen equation for vaporization was developed and used to simulate the ablation of TiC by Nd:YAG and KrF pulsed laser radiation. The calculations were performed for fluences of 8 and 10 J/cm², which according to experimental results obtained previously, correspond to large increases of the ablation rate. The calculated maximum surface temperature of the target for both lasers is higher than the estimated value of TiC critical temperature, corroborating the hypothesis that the increase of the ablation rate is explained by the explosive boiling mechanism.     

Plasma-mediated ablation of biofilm contamination

Ultra-short pulsed laser removal of thin biofilm contamination on different substrates has been conducted via the use of plasma-mediated ablation. The biofilms were formed using sheep whole blood. The ablation was generated using a 1.2 ps ultra-short pulsed laser with wavelength centered at 1552 nm. The blood contamination was transformed into plasma and collected with a vacuum system. The single line ablation features have been measured. The ablation thresholds of blood contamination and bare substrates were determined. It is found that the ablation threshold of the blood contamination is lower than those of the beneath substrates including the glass slide, PDMS, and human dermal tissues. The ablation effects of different laser parameters (pulse overlap rate and pulse energy) were studied and ablation efficiency was measured. Proper ablation parameters were found to efficiently remove contamination with maximum efficiency and without damage to the substrate surface for the current laser system. Complete removal of blood contaminant from the glass substrate surface and freeze-dried dermis tissue surface was demonstrated by the USP laser ablation with repeated area scanning. No obvious thermal damage was found in the decontaminated glass and tissue samples.     

Laser cleaning of stone by different laser pulse duration and wavelength

The present work focuses on the main phenomenological features of stone cleaning by lasers. These are the removal rate, cleaning degree, and chromatic appearance of the treated surface associated with different conservation problems and laser parameters. A set of three different outdoor stone conservation problems were investigated here. The measurement of the ablation rates were carried out on encrusted stone artifacts and two sets of standards in order to derive general behaviors through repeatable measurements. The analysis of the irradiation tests provided quantification of the different efficiencies, cleaning degree, and chromatic appearances associated with the fundamental harmonic of Q-switching, long Q-switching, and short free-running Nd:YAG lasers (1064 nm), as well as with the second harmonic of Q-switching sources (532 nm).     

Pulsed laser deposition—UV laser sources and applications

Progress in material research and processing industry is fueled by the technique of pulsed laser deposition (PLD). High energy excimer lasers enable this technique since every material is amenable to their high photon energies. Spectral properties, temporal pulse and laser beam parameters of state of the art excimer lasers will be compared with frequency converted Nd:YAG lasers. Both quality and longevity of the deposited layers strongly depend on the degree of accuracy achieved in the thin film ablation and subsequent deposition process.     

Selective ablation of thin Mo and TCO films with femtosecond laser pulses for structuring thin film solar cells

We report on recent results on selective ablation of TCO (SnO₂, ZnO) and metallic layers as a possible process for structuring thin film solar cells. The multipulse ablation thresholds determined for substrate and various thin films show a parameter window where the films can be completely removed by a single scan without at the same time damaging the underlying material. By employing ultrashort pulsed lasers, nonthermal ablation at repetition rates up to the megahertz regime enables high quality structuring combined with process speeds meeting industrial demands. PACS 42.65.Re; 42.55.Xi; 42.62.-b; 84.60.Jt     

Generation of ultrasound in materials using continuous-wave lasers

Generating and detecting ultrasound is a standard method of nondestructive evaluation of materials. Pulsed lasers are used to generate ultrasound remotely in situations that prohibit the use of contact transducers. The scanning rate is limited by the repetition rates of the pulsed lasers, ranging between 10 and 100 Hz for lasers with sufficient pulse widths and energies. Alternately, a high-power continuous-wave laser can be scanned across the surface, creating an ultrasonic wavefront. Since generation is continuous, the scanning rate can be as much as 4 orders of magnitude higher than with pulsed lasers. This paper introduces the concept, comparing the theoretical scanning speed with generation by pulsed laser.     

Characterization of aerosol plumes in nanosecond laser ablation of molecular solids at atmospheric pressure

Ablation of molecular solids with pulsed ultraviolet lasers at atmospheric pressure is an important process in (bio-)organic mass spectrometry. Of practical importance for analytical sampling and analysis are the plume formation and expansion. Plumes formed by atmospheric-pressure laser ablation of anthracene and 2,5-dihydroxybenzoic acid (2,5-DHB) were studied by light scattering imaging, which showed significant material release in the form of aerosols. The monitored plume expansion dynamics could be fitted to the drag-force model, yielding initial plume velocities of 150 m/s for anthracene and 43 m/s for DHB. While the angle of incidence does not affect the plume direction and propagation, a large dependence of the plume-expansion velocity on the laser pulse energy could be found, which is limited at atmospheric pressure by the onset of plasma shielding. With respect to analytical applications, the efficiency of sampling of the laser ablation products by a capillary could be experimentally visualized.     

Enhancement of ablation rate and production of colloidal nanoparticles by irradiation of metals with nanosecond pulsed laser in presence of external electric field

This paper presents the results of experimental study on the effect of electric field on the ablation rate during the nanosecond pulsed laser ablation of aluminum and copper in deionized water. The effect of electric field strength on the material removal rate and its mechanisms were investigated both in the electric field parallel and perpendicular to the laser beam path schemes. The ablation rate was estimated by measuring the dimensions of craters on the target induced by laser. The crater dimensions and optical properties of the produced colloidal nanoparticles were characterized by means of optical microscopy and UV–Vis absorption spectroscopy, respectively. The results indicate that pulsed laser ablation in the presence of an electric field significantly leads to higher material removal rate. The experimental results also confirm that the crater geometry extremely depends on the direction of the electric field with respect to the laser beam direction. The UV–Vis spectra show that the nanoparticles production efficiency increases with increasing the electric field strength.