Tissue ablation through water with erbium: YAG lasers

We report the dynamics of vapor cavities generated by 200 microseconds long Er:YAG laser pulses under water and in gelatin. Acoustic transients were detected at the beginning of the laser pulse and when the cavity collapsed. Cavity expansion and collapse, and the associated acoustic transients are possible ablation mechanisms with the Er:YAG laser. Shortening of the pulse duration is suggested to minimize long range under water tissue damages.     

不同盐度海水的光击穿声辐射特性研究

强激光聚焦于水下时,通过光击穿机制辐射强声波信号。水体介质的盐度不同,在同等的激光参数、光学系统条件下,光击穿辐射的声波在强度、脉冲波形、频谱特征上具有一定的差异性。为研究水介质盐度对激光击穿形成的空泡辐射声波的影响,构建了激光声测量系统,实验研究了不同水体盐度参数对光击穿辐射声信号的影响。结论：激光击穿水介质伴随空泡脉动、声信号辐射效应;激光声信号脉冲宽度与水体盐度无关;空泡尺寸和激光声信号强度与激光脉冲能量成正比关系;水体盐度与激光声信号的强度早非线性变化关系。研究结果有助于激光声在海洋中的应用。     

Combined ultrasound and optoacoustic system for real-time high-contrast vascular imaging in vivo

In optoacoustic imaging, short laser pulses irradiate highly scattering human tissue and adiabatically heat embedded absorbing structures, such as blood vessels, to generate ultrasound transients by means of the thermoelastic effect. We present an optoacoustic vascular imaging system that records these transients on the skin surface with an ultrasound transducer array and displays the images online. With a single laser pulse a complete optoacoustic B-mode image can be acquired. The optoacoustic system exploits the high intrinsic optical contrast of blood and provides high-contrast images without the need for contrast agents. The high spatial resolution of the system is determined by the acoustic propagation and is limited to the submillimeter range by our 7.5-MHz linear array transducer. A Q-switched alexandrite laser emitting short near-infrared laser pulses at a wavelength of 760 nm allows an imaging depth of a few centimeters. The system provides real-time images at frame-rates of 7.5 Hz and optionally displays the classically generated ultrasound image alongside the optoacoustic image. The functionality of the system was demonstrated in vivo on human finger, arm and leg. The proposed system combines the merits and most compelling features of optics and ultrasound in a single high-contrast vascular imaging device.     

Comparison of the effects of absorption coefficient and pulseduration of 2.12-μm and 2.79-μm radiation on laser ablation oftissue

Erbium and holmium lasers are attractive for minimally invasive surgical applications as they operate at wavelengths where tissues exhibit strong absorption due to their water content and because these wavelengths are transmittable through optical fibers. In this study, the basic physical mechanisms underlying tissue ablation and the laser-induced tissue effects using pulsed Er:YSGG (2.79 μm) and Ho:YAG (2.12 μm) laser radiation are presented and compared, Q-switched (τ=40 ns, E⩽50 mJ) and free-running (τ=250 and 400 μs) Er:YSGG (E=100 mJ) and Ho:YAG (E⩽1 J) laser energy was delivered in water via a 400-μm fiber. The dimension and lifetime of the expanding and collapsing bubbles and the laser-induced pressure in water after each laser pulse were measured with fast-flash videography and time-resolved pressure measurements. Depending on the absorption coefficient, pulse energy, and pulse duration, three different regimes were distinguished: evaporation, tensile-stress-induced cavitation, and explosive vaporization. In vitro tissue effects, ablation depth, and extent of tissue damage on meniscus treated under water and on cornea treated in air were investigated and examined histologically. Er:YSGG radiation, due to its 100 times higher absorption than Ho:YAG radiation, exhibited a high tissue ablation efficiency with a relatively small zone of coagulated tissue (Q-switched 4-10 μm, free-running less than 100 μm), whereas the coagulated tissue zone was 300-1000 μm after free-running and 100-120 μm after Q-switched Ho:YAG laser impact     

Femtosecond laser-tissue interactions: Retinal injury studies

We report the first study of laser-tissue interaction in the femtosecond time regime. Retinal damage thresholds and mechanisms produced by exposure to high-intensity femtosecond laser pulses were investigated in chinchilla grey rabbits. Exposures were performed using single laser pulses of 80 fs duration at 625 nm. ED50injury thresholds of 0.75 and 4.5 μJ were measured using fluorescein angiographic and ophthalmoscopic visibility criteria evaluating 204 laser exposures. Ultrastructural studies including light and electron microscopy were performed on selected lesions. Results suggest that the primary energy deposition in the retina occurs in melanin, However, in contrast to laser injuries produced by longer pulses, exposures of more than 100 × threshold in the50-100 muJ range did not produce significantly more severe lesions or hemorrhage. This suggests the presence of a nonlinear damage limiting mechanics in tissue exposed to femtosecond laser pulses.     

193nm准分子激光及超短脉冲激光角膜切削

193nm准分子激光和费秒级超短脉冲激光因其能对角膜进行精确的切削 ,对临近组织造成的损伤很小 ,已经成为屈光手术领域研究的热点。本文首先研究 193nm准分子激光 ,费秒级超短脉冲激光对角膜的切削机理 ,建立激光脉冲参数与角膜组织切削量之间的数学模型并在此基础上对比分析两种激光切削角膜的特征及其在屈光手术领域的应用。     

Surface and bulk structuring of materials by ripples with long and short laser pulses: Recent advances

Ripples are formed on the surface of solid materials after interaction with laser pulses of high intensity/irradiance. When ultra-short sub-1 ps laser pulses are used, the observed morphology of ripples on surfaces becomes much more complex as compared with ripples formed by long laser pulses. Uniquely for the short laser pulses, ripples can be formed in the bulk. A better understanding of the fundamentals of light-matter interaction in ripples formation is strongly required. Experimentally observed ripples and dependence of their parameters on laser fabrication conditions and material properties are summarized first. Then, a critical review of relevant ripple formation mechanisms is presented, discussed, and formation conjectures are presented.     

Mechanisms of biliary stone fragmentation using the Ho:YAG laser

The authors have investigated the fragmentation of gallstones using the pulsed Ho:YAG laser, comparing it to lithotripsy using the visible pulsed-dye laser. They find that the physical mechanisms of stone fragmentation appear to be quite different in the two cases. Using high-speed photography, measurement of acoustic transients, time-resolved optical emission spectroscopy, and direct microscopic observation, the authors have analyzed the interaction of the Ho:YAG laser with both water and gallstones. They propose a new model in which fragmentation begins with absorption of the laser light by the stone surface. This is followed by melting and ejection of stone material, which is then swept away by the vapor bubble formed by the absorption of the Ho:YAG laser light by water. This model is in excellent agreement with the authors' experimental observations, and differs substantially from the model developed by P. Teng et al. (1987) for laser lithotripsy using the visible pulsed-dye laser     

激光脉冲波形对液体中热膨胀机制致声特性的影响

首先阐述了激光与液体媒质作用通过热膨胀机制激发平面光声源的理论;分别针对激光脉冲为正弦波形、三角波形和高斯波形的情况,推导了激光脉冲分别在约束界面和自由界面下产生声脉冲的解析解,然后通过仿真得到了激发声波的光声脉冲剖面和时空分布图;并对比分析了正弦波形、三角波形和高斯波形的激光脉冲分别在约束边界和自由边界下激发声波的峰值声压、光声转换效率和波形等特性.     

A novel method for sub-micron particle detection in clean liquids

A novel approach to the detection of liquid-borne submicrometer particles (extendible to ultra-clean liquids) is described. The key concept is to coax the submicrometer particles to soft cavitate and then detect the ensuing transient bubble activity acoustically rather than the particle itself (which has only a weak scattering signature). The method, therefore, relies on facilitating acoustic microcavitation through acoustic coaxing. Acoustic microcavitation is brought about by low megahertz acoustic fields giving rise to micrometer-size bubbles that live a few microseconds. Liquid-borne microparticles do not, ordinarily, cause any cavitation when exposed to strong sound fields (of 1 MHz). If, however, a very weak, high-frequency auxiliary acoustic field (e.g., 30 MHz) is added to this sound field, cavitation by the microparticles is readily facilitated. This technique of facilitating cavitation is referred to as “acoustic coaxing”. Results of preliminary experiments indicate that even smooth spherical microparticles can be coaxed to cause cavitation. An explanation of the “acoustic coaxing effect” is offered. The physics seems not to be limited by the smallness of microparticles (effect possible up to 50 nm). This novel method based on acoustic coaxing of microcavitation promises to be a good basis for on-line, real time monitoring of liquid-borne submicronic particulates. This method is not limited to small sensing volumes and, unlike optical methods, it has an intrinsic, location specific, signal enhancement at the source particle     

XeCl激光泵浦的ns染料激光器

报道了以XeCl准分子激光作泵浦源,通过所谓的“控制腔瞬态过程”的方法,直接获得ns染料激光脉冲的实验结果。与N_2光泵浦比较,XeCl激光泵浦可得到更短波长和更高阈值系统的激光振荡。     

Effect of melting on the acoustic response of CdTe and GaAs subjected to the pulsed laser irradiation

The effect of a threshold process of surface melting on the acoustic response in CdTe and GaAs subjected to pulsed laser radiation is considered and the mechanisms of excitation of sonic signals are analyzed. Melting thresholds of the surface of binary compounds CdTe and GaAs are established under irradiation by pulses of nanosecond duration of ruby and neodymium lasers from measurements of the amplitude of the acoustic response.     

基于MLP神经网络的圆锥角膜辅助诊断北大核心CSCD

圆锥角膜在病变过程中会导致角膜中央部位向前凸出,使角膜呈现出圆锥形,而且会导致高度不规则近视和散光,对视力造成不同程度损害。疾病一般发生于青少年时期,为了能及时治疗避免病变严重,筛查区分圆锥角膜具有十分重要的意义。而且临床上对于圆锥角膜诊断通常是采用角膜地形图的方法,可以得到角膜形态学的改变,但是有一定的误诊率。目前研究发现,角膜力学特性改变先于形态学,所以本文从角膜生物力学角度出发,提出一种基于多层感知机(multi-layer perceptron,MLP)神经网络区分圆锥角膜的模型。首先,利用可视化生物力学分析仪(corneal visualization scheimpflug technology,Corvis-ST)测得角膜的生物力学视频,进行处理计算得到角膜生物力学参数作为数据集,其中包含正常角膜和圆锥角膜2种类别;然后,针对角膜生物力学参数数据集构建MLP神经网络模型,将70%数据集作为训练集,30%数据集作为测试集。在数据集上训练及测试的结果表明,该模型区分圆锥角膜的准确率为97.6%。     

IL-1ra对激光角膜烧伤的治疗作用

白介素1受体拮抗剂(IL-1ra)可阻断IL-1在机体的免疫应答、感染、炎症反应和组织损伤中的作用.采用日本大耳白兔,造成角膜激光烧伤模型,观察研究LI-1ra的治疗作用.通过裂隙灯与病理组织学观察,角膜OD值与角膜上皮细胞活性测定,以及烧伤斑图像分析,实验结果表明,IL-1ra对激光角膜烧伤具有一定疗效.     

慢病毒载体介导增强型绿色荧光蛋白两种途径体内转染大鼠角膜基质细胞有效性的试验研究

目的:观察慢病毒载体介导的增强型绿色荧光蛋白(lenti-EGFP)通过两种途径体内转染大鼠角膜基质细胞的有效性,为角膜疾病尤其是准分子激光术后角膜Haze形成的基因治疗提供实验基础.方法:Lenti-EGFP通过角膜基质注射和刮除角膜上皮敷贴带lenti-EGFP的棉片两种不同方法体内转染大鼠角膜基质细胞,转染后定期...     

双脉冲激光对生物组织的热和声损伤机理研究

本文从提高治疗效果减小生物组织声损伤和提高激光的能量利用率考虑，提出双脉冲治疗皮肤色素性病损的方法，并建立皮肤组织的热传导模型，对多脉冲治疗时生物组织的热损伤和声损伤进行的理论分析，表明双脉冲治疗可以提高疗效，减小生物组织的声损伤。同时，为减小组织的热损伤，脉冲间隔最小应为4倍的组织热驰豫时间。经病理实验得到验证。实验中双脉冲激光为200微秒。     

准分子激光与角膜组织的相互作用及在屈光矫正中的应用

准分子激光在屈光手术中获得了迅速发展，193nm的准分子激光刻蚀角膜表面，改变角膜表面的光学结构从而矫正屈光不正，而且由于其微小的力学和热效应，不会损伤邻近组织。本文研究了激光和生物组织的相互作用，定性确定了光斑与角膜表面粗糙度关系，定量分析了193nm准分子激光高斯光束的切削量与能量密度的关系，在此基础上，给出准分子激光应用到眼科治疗机中的原理图、屈光程度与激光消融量的关系和具体算法，最后通过PMMA板的实验验证，并已应用到临床，取得了良好的效果。     

重复激光脉冲作用下薄膜损伤演化规律研究

为了深入研究重复激光脉冲的能量效应对光学薄膜的烧蚀机理,采用实验观测与热力学分析相结合的方法进行了研究。通过观察光学薄膜烧蚀形貌随入射激光脉冲数量增加发生改变的典型形貌特征,分析了激光与等离子体相互作用的热力学过程,得到了在激光重复脉冲作用下光学薄膜的损伤特性及其演化规律。结果表明,薄膜在重复脉冲作用下,其表面会变得粗糙,这会大大增加对激光的吸收效应,从而加速了薄膜的破坏,最终被完全去除而露出基底;同时,烧蚀物会在热膨胀作用下向激光作用区域外扩散,在激光烧蚀中心区域外进行沉积,而形成更大范围的污染。由于激光光强为高斯分布,重复脉冲作用的效应主要是对在光束中心区域的薄膜进行集中烧蚀,会不断增加烧蚀的损伤程度,而对烧蚀面积的增加效应极为有限。这一研究结果为重复激光脉冲对薄膜烧蚀机理的建立提供了参考。     

不同环境压强下激光空泡特性研究

构建了激光空泡测量实验平台,使用脉冲激光聚焦击穿水介质产生激光空泡,由水听器对激光空泡溃灭辐射声信号进行接收,利用充气泵对高压水箱内的气压进行精确控制。通过仿真计算和实验对不同环境压强下的激光空泡特征和其溃灭时辐射声信号的峰值变化特性进行了研究。结果表明:当环境压强处在0.1~0.7 MPa 范围内变化时,随着环境压强的增大,激光空泡首次脉动周期和空泡最大半径逐渐减小,两者的变化速率逐渐减小。空泡溃灭时辐射声信号的峰值声压在0.1~0.4 MPa内逐渐增大,在0.4~0.7MPa 内逐渐减小,且增大速率大于减小速率。     

激光脉冲串对电荷耦合器件积累损伤效应研究

为了研究激光脉冲串对光电系统的损伤和致盲机理,开展了重频纳秒激光对黑白行间转移相机电荷耦合器件的损伤实验研究。实验结果表明:存在两种积累损伤效应机理,多个脉冲到达CCD靶面同一位置的损伤或致盲具有积累效应,多个脉冲积累损伤能够显著降低线损伤和全靶面损伤阈值,降低程度与脉冲个数、激光到靶能量密度有关。致盲机理与单脉冲致盲机理相同,均表现为器件垂直转移电路间及地间的短路;而激光脉冲串到达CCD靶面的不同位置也能够实现器件的功能性失效,其机制与单脉冲损伤显著不同,仅表现为线损伤的叠加,并未造成器件电路紊乱,功能性损伤阈值即对应线损伤阈值660 mJ/cm2,而小于单次致盲阈值1 500~2 200 mJ/cm2。