A molecular dynamics investigation into the mechanisms of material removal and subsurface damage of nanoscale high speed laser-assisted machining

Molecular dynamics is employed to study the mechanism of material removal and subsurface damage of monocrystalline silicon when it is under a nanoscale high-speed laser-assisted grinding of a diamond tip. Laser-assisted machining (LAM) is that the workpiece is locally heated by an intense laser beam before material removal. The effects of laser moving speed, laser pulse intensity and laser spot radius are thoroughly investigated in terms of atomic trajectories, phase transformation, temperature distribution, grinding temperature, grinding force and friction coefficient. The investigation shows that a higher laser moving speed reduces the subsurface damage and improves the material remove rate because of fewer atoms with five and six coordination atoms and more chips. Besides, both tangential grinding force (Fx) and normal grinding force (Fy) decrease as the laser moving speed increases. The distribution of high-temperature zone strongly depends upon the effect of laser pulse intensity and laser spot radius. Larger laser pulse intensity can make the material more fully softened before being removed. Moreover, as the laser pulse intensity becomes larger, the friction coefficients became smaller, the material remove rate improves and the depth of grinding increases. However, larger laser pulse intensity may result in a larger thermal deformation of workpiece. A larger laser spot radius reduces the grinding depth but increases the width of laser irradiation zone on machined surface. Thus, a suitable laser spot radius can improve the material removal rate. These results indicate that it is possible to control and adjust the laser parameters according to laser moving speed, laser pulse intensity and laser spot radius, and it provides a potential technology to improve a surface integrity and a smoothness of ground surface.     

532 nm和808 nm激光及其线偏振激光辐照人正常膀胱与膀胱癌组织光学特性

采用双积分球系统和光辐射测量技术的基本原理 ,以及运用生物组织的光学模型 ,研究了 5 32nm和80 8nm激光及其线偏振激光辐照人正常膀胱和膀胱癌组织的光学特性 .结果表明 :膀胱癌组织对同一波长的激光或其线偏振激光的衰减明显较正常膀胱组织的要大 ,膀胱癌组织对 5 32nm和 80 8nm激光的衰减均较其线偏振激光的要略大一些 .膀胱癌组织对 5 32nm和 80 8nm激光及其线偏振激光的衰减明显较正常膀胱组织的要大 .正常膀胱或膀胱癌组织对同一波长的激光及其线偏振激光的折射率均没有明显的差异 ,膀胱癌组织对 5 32nm和80 8nm激光的折射率比正常膀胱的明显要大 .Kubelka Munk二流模型下 ,两种组织对同一波长的激光或其线偏振激光的光学特性均有显著性差异 (P <0 0 1) .同一组织对不同波长的激光及其线偏振激光的光学特性也有显著性差异 (P <0 0 1) ,正常膀胱组织对同一波长的激光及其线偏振激光的光学性有明显差异 ,而膀胱癌组织对同一波长的激光及其线偏振激光的光学特性则没有明显差异 .膀胱癌组织对 5 32nm和 80 8nm激光及其线偏振激光的前向散射通量i (x)、后向散射通量 j (x)、总散射通量I (x)的衰减均较正常膀胱组织的明显要大得多 ,且其i (x)均明显较j (x)要强     

激光采血的分析研究

本文根据激光与皮肤组织的作用规律对紫外激光,可见激光和红外激光的采血效果进行了系统地分析研究,研究结果表明：CO2激光与Er:YAG激光是采血的理想工具。并对红外激光采血的参娄进行了定量地分析与计算,为激光采血设备的研制和应用提供一个参考。     

我国植物激光诱变育种的概况

我国植物激光育种１９７２年以来,共用１４种激光器处理了４５种植物,育成了４２个新品种,激光器的诱变效果,以Ｈｅ－Ｎｅ和ＣＯ２激光最好。     

Q开关Nd:YAG 1064nm和532nm激光对犬心肌切割作用的研究

目的 :研究 10 64nm和 53 2nm波长激光在激光能量为 14 0mJ/pulse(脉冲 )时对犬心肌切割效率。方法 :用Q开关Nd :YAG 10 64和 53 2nm波长脉冲激光分别照射犬离体和在体心肌组织 ,光学显微镜和偏振光学显微镜行组织学分析 ,观察不同条件下激光切割组织的深度和光热对组织的损伤。结果 :离体和在体实验 ,10 64nm波长激光的切割效率高于 53 2nm(p <0 .0 1)。在体和离体实验显示 10 64nm激光能量和重复率相同时 ,所致的切割效率无明显差异 (p >0 .0 5) ,血液对 10 64nm激光的切割效率影响较小。相反 ,在 53 2nm时血液对其影响较大 ,相同的激光能量和重复率 ,离体实验切割效率高于在体 (p <0 .0 1)。 10 64nm激光所致的光热和机械损伤均轻于 53 2nm激光。结论 :在切割效率方面 ,10 64nm激光比 53 2nm更适用于TMLR。 10 64nmQ开关Nd :YAG激光可通过光导纤维传输 ,是TMLR的一个有潜力的激光源     

激光在农作物遗传育种上的应用

本文论述了激光的作用原理包括光效应,热效应,压力效应和激光的应用包括小剂量激光对农作物的刺激作用,大剂量激光的诱变作用,其它诱变剂复合使用的诱变作用,并评述了激光在水稻,小麦,油菜、大麦、大豆及果树,蔬菜,桑等的研究进展,最后阐述了激光在农作物遗传育种上的应用前景。     

激光在农业领域应用研究进展

本文综述了近年来激光在农业领域的研究概况,如激光生物学刺激效应、激光诱变育种,激光辐照离体质粒DNA、激光微束转基因技术等,并对有待进一步研究解决的问题进行了讨论。     

532nm 激光血管内照射血液实验方法

根据现有的低强度５３２ｎｍ激光器的输出特性,建立了简便、可靠的激光血管内照射血液实验方法。通过选择合适的滤光片,可以确保５３２ｎｍ激光的单纯性;通过分束监视,实现了激光输出功率的准确计量;在实验过程中,根据监视功率值对激光输出功率进行实时调节,可以使其比较稳定地保持在设定附近。该实验方法亦可供其它激光生物效应实验参考。     

国产Nd:YAP激光组织热损伤效应的比较研究

目的:通过比较1 341 nm Nd:YAP与临床常用激光器脉冲Nd:YAG和连续Nd:YAG对皮肤、肌肉、静脉和肝脏组织的热损伤效应,了解Nd:YAP激光的作用特点,为其临床应用提供实验依据。方法:以大鼠作为实验对象,分为皮肤、肌肉组和静脉、肝脏组。皮肤、肌肉组:Nd:YAP激光、连续和脉冲Nd:YAG选择能量密度1000 J/cm2、2 000 J/cm2,静脉、肝脏组采用Nd:YAP激光和连续Nd:YAG两种激光器,能量密度选择500 J/cm2和1 000 J/cm2,对组织进行非接触式点状照射。照射过程中观察组织变化和损伤直径大小,并于照射后即刻、3天取材做病理切片,光镜下观察病理变化,比较相同能量密度下三种激光器对组织的热损伤和损伤修复情况。结果:皮肤、肌肉组:Nd:YAP激光在1 000 J/cm2条件下对组织的损伤以热凝固效应为主,2 000 J/cm2条件下组织发生明显气化、有一定的切割作用。相同能量密度下,脉冲Nd:YAP激光气化作用较两种Nd:YAG激光显著,而凝固损伤范围较连续Nd:YAG浅,较脉冲Nd:YAG深。肝脏、静脉组:Nd:YAP激光对肝脏的热凝固效应与Nd:YAG激光近似,气化作用明显;Nd:YAP激光对血管及其周围组织的凝固及气化作用均较连续Nd:YAG激光明显。结论:Nd:YAP激光具有良好的凝固与气化作用。     

Immunomodulatory effect of laser on whole body exposure.

All biomedical laser applications are based on the interaction of laser light with biological system. During the past decade considerable evidence has accumulated demonstrating that non-thermal exposure to laser can elicit cellular changes in the immune system. In the present study, we have analyzed the effect of laser on immune response in rats. A group of rats were exposed to 0.225 mu j/cm2 for 90 min for 3 days in specially designed fiberglass chambers. The whole body exposure of rats of He-Ne laser modulated both the humoral and cellular responses to tetanus toxoid stimulation. Plain red light used as a control for red laser light showed an appreciable degree of response as compared to the control groups, but not to the extent of the response to laser. Non-responders turned responders after exposure to laser. There was no response in unimmunized groups when exposed to laser and red light alone. The early and heightened immune response and proliferation of lymphocytes after exposure to laser is suggestive of a complex interaction at the cellular immune response level.     

Molecular level damages of low power pulsed laser radiation in a marine bacterium Pseudoalteromonas carrageenovora

AIM: To study the molecular level damages in a marine bacterium, Pseudoalteromonas carrageenovora, exposed to low power pulsed laser radiation from an Nd:YAG laser. METHODS AND RESULTS: The laser damages in bacterial DNA were monitored by studying the formation of apurinic/apyrimidinic (AP) sites. Molecular probe kits were used for this purpose. Occurrence of lesions in the cell walls was monitored under a transmission electron microscope (TEM). The results showed that laser radiation significantly increased the number of AP sites in the bacterial DNA. This increase corresponded to the laser fluence (J cm(-2)) and to the duration of laser irradiation. TEM observation showed the occurrence of lesions in bacterial cell walls upon laser irradiation. CONCLUSIONS: It is concluded that bacteria exposed to laser irradiation suffers DNA damages and resulted in broken cell walls. These events led to bacterial mortality. These are in addition to the mechanisms reported earlier such as the photochemical reactions occurring inside the cells upon exposure to low power laser. SIGNIFICANCE AND IMPACT OF THE STUDY: These results help us to understand the mechanisms of bacterial mortality on exposure to low power pulsed laser irradiation and are useful in formulating a laser treatment strategy to kill bacteria.     

准分子激光眼科治疗机中激光器控制实现

准分子激光眼科治疗机可以用来进行近视、远视、散光等屈光不正的矫正手术。其中激光器的控制为手术提供能量稳定的激光脉冲,是对手术安全性、可靠性的重要保证。本文简述了一准分子激光眼科治疗机的整体组成部分,并详细描述了激光器的控制部分:计算机与激光器的通信控制、激光发射停止控制、充换气流程控制。目前,这种准分子激光治疗机已经应用于临床,并取得了良好的效果。     

低强度激光鼻腔照射对血脂异常作用的研究

目的：观察低强度激光（650nm／5mw）鼻腔照射疗法对血脂异常的作用。方法：30例原发性血脂异常患者随机分为两组,分别接受药物（舒降之）治疗和低强度激光鼻腔照射疗法,测定治疗前后的血脂水平。结果：在调整饮食的基础上,低强度激光经鼻腔照射使病人的血清总胆固醇水平降低了5．8％（P=0．031）,甘油三酯降低了8．8％;低强度激光鼻腔照射在有效调整血脂的同时,使谷丙转氨酶（J唧）水平下降了23．1％（P=0．022）,对肝功能具有保护作用。结论：与舒降之相比,低强度激光鼻腔照射疗法的调脂效果虽然相对较弱,但基于安全性的考虑,在饮食控制无效或肝功能异常的病人中使用低强度激光鼻腔照射仍然具有一定的应用价值。     

激光对生物组织热和热致机械损伤的物理分析

从物理学角度阐明激光照射生物组织时在组织中形成热源的微观机制,系统分析这一热源对生物组织所产生的正、反两方面的作用,并进行量化描述,其结果对揭示和理解激光照射生物组织时所产生的宏观效应以及激光医疗应用都有积极作用。     

激光及激光生物学发展概况

本文介绍了激光、激光应用和激光生物学发展概况     

Characterizing Far-infrared Laser Emissions and the Measurement of Their Frequencies

The generation and subsequent measurement of far-infrared radiation has found numerous applications in high-resolution spectroscopy, radio astronomy, and Terahertz imaging. For about 45 years, the generation of coherent, far-infrared radiation has been accomplished using the optically pumped molecular laser. Once far-infrared laser radiation is detected, the frequencies of these laser emissions are measured using a three-laser heterodyne technique. With this technique, the unknown frequency from the optically pumped molecular laser is mixed with the difference frequency between two stabilized, infrared reference frequencies. These reference frequencies are generated by independent carbon dioxide lasers, each stabilized using the fluorescence signal from an external, low pressure reference cell. The resulting beat between the known and unknown laser frequencies is monitored by a metal-insulator-metal point contact diode detector whose output is observed on a spectrum analyzer. The beat frequency between these laser emissions is subsequently measured and combined with the known reference frequencies to extrapolate the unknown far-infrared laser frequency. The resulting one-sigma fractional uncertainty for laser frequencies measured with this technique is ± 5 parts in 10⁷. Accurately determining the frequency of far-infrared laser emissions is critical as they are often used as a reference for other measurements, as in the high-resolution spectroscopic investigations of free radicals using laser magnetic resonance. As part of this investigation, difluoromethane, CH₂F₂, was used as the far-infrared laser medium. In all, eight far-infrared laser frequencies were measured for the first time with frequencies ranging from 0.359 to 1.273 THz. Three of these laser emissions were discovered during this investigation and are reported with their optimal operating pressure, polarization with respect to the CO₂ pump laser, and strength.     

Laser induced cell fusion in combination with optical tweezers: the laser cell fusion trap.

A single-beam gradient force optical trap was combined with a pulsed UV laser microbeam in order to perform laser induced cell fusion. This combination offers the possibility to selectively fuse two single cells without critical chemical or electrical treatment. The optical trap was created by directing a Nd:YAG laser, at a wavelength of 1.06 microns, into a microscope and focusing the laser beam with a high numerical aperture objective. The UV laser microbeam, produced by a nitrogen-pumped dye laser (366 nm), was collinear with the trapping beam. Once inside the trap, two cells could be fused with several pulses of the UV laser microbeam, attenuated to an energy of approximately 1 microJ/pulse in the object plane. This method of laser induced cell fusion should provide increased selectivity and efficiency in generating viable hybrid cells.     

Vacuum electron acceleration by a tightly focused,radially polarized,relativistically strong laser pulse

A test particle approach is used to solve the problem of direct electron acceleration by a short, intense, radially polarized laser pulse the focal spot diameter of which can be on the order of the laser wavelength. The fields of a tightly focused laser beam are described in terms of the Stratton-Chu integrals, with which to investigate electron acceleration when the paraxial approximation is inapplicable to laser fields. The dynamics of electron motion in a radially polarized, relativistically strong laser field is analyzed depending on the initial position of an electron in the focal region of the laser beam. The properties of the generated jets of accelerated electrons are investigated depending on the tightness of laser pulse focusing. Possible advantages of using radially polarized laser pulses for charged particle acceleration, as opposed to the use of linearly polarized ones, are discussed.     

激光技术在农产品质量检测中的研究进展

近年来激光在农业领域得到广泛的应用和研究,其中的一个最新进展是将激光技术应用于农产品内部品质和安全性检测。本文介绍了农产品质量检测中的几种激光技术,包括应用激光的吸收与反射技术来检测农产品糖酸度、质地、PH值、成熟度、干物质等;应用激光诱导荧光技术来检测农产品的农药残留、叶绿素、成熟度;应用激光拉曼光谱技术来检测农产品水果损伤、农药残留。对农产品激光检测的未来发展趋势进行了探讨和展望。     

The production of short-lived free radicals accompanying laser photoablation of cardiovascular tissue

Using the method of spin trapping and electron paramagnetic resonance, free radicals have been detected accompanying laser ablation of cardiovascular tissue. Radicals were detected using both visible and ultraviolet laser energy from argon-ion and excimer laser sources. The results are discussed in terms of the relative efficiency of the laser wavelengths to produce free radicals and a comparison of the types of radicals produced by the action of pulsed versus cw laser energy.