Generation of calcium waves in living cells induced by 1 kHz femtosecond laser protuberance microsurgery

We have demonstrated that intracellular calcium waves in a living olfactory ensheathing cell (OEC) can be induced by femtosecond laser surgery on cellular protuberance. In this paper, calcium wave generation mechanisms are further investigated using different culture mediums and protuberance diameters. The protuberances of living OECs are cut by home-made 1 kHz femtosecond laser surgery system with 130 fs pulsewidth and 800 nm wavelength, and the average power of 200 μW is chosen for stable and effective cell surgery. Whether the cells are cultured in mediums with Ca²⁺ or not, intracellular calcium waves can be induced after cell surgery. The generation of calcium waves is independent on the dimension of protuberance diameter. Based on these results, we analyze generation mechanisms of calcium wave and conclude that shockwave-induced mechanical force and laser-induced cytoskeleton depolymerization are two key factors.     

Realignment process of actin stress fibers in single living cells studied by focused femtosecond laser irradiation

Three-dimensional dissection of a single actin stress fiber in a living cell was performed based on multi-photon absorption of a focused femtosecond laser pulse. The realignment process of an actin stress fiber was investigated after its direct cutting by a single-shot femtosecond laser pulse irradiation by high-speed transmission and fluorescence imaging methods. It was confirmed that mechanical force led by the femtosecond laser cutting propagates to entire cell through the cytockelton in a 100 μs time scale. The cut actin stress fiber was realigned in the time scale of a few tens of minutes. The dynamic analysis of the realignment induced by single-shot femtosecond laser gives new information on cell activity.     

Nonlinear optical effects of near-IR femtosecond laser radiation on the morphology and structure of a nerve cell in the field of an optical trap

Changes in the morphology and structure of a neuron cell in the process of manipulating it with an femtosecond laser tweezers operating at a wavelength of 800 nm are examined. The changes in the morphology and structure are caused by the nonlinear optical absorption and multiphoton excitation of cell biomacromolecules by femtosecond pulses of light. The cell nucleus is demonstrated to be destroyed by focused femtosecond laser radiation (FLR). Changes in the state of the cytoplasmic nucleoproteins and the hydrophobicity of the plasmatic membrane under the action of FLR focused inside the cell are observed. By the example of the simultaneous displacement of the neuron with a cw laser and cutting of a neuron with FLR, the operation of holographic optical manipulator and a scalpel based on the use of femtosecond and cw lasers is considered. The possibility of the simultaneous microsurgical operation with several optical foci of FLR is demonstrated.     

飞秒激光烧蚀0Cr18Ni9不锈钢精度的影响因素

为了研究影响飞秒激光烧蚀0Cr18Ni9不锈钢精度的因素,采用飞秒激光对0Cr18Ni9不锈钢进行了切割和打孔实验。利用光学显微镜、光学金相显微镜等设备,对不锈钢烧蚀区形貌和切缝显微组织进行检测,基于烧蚀过程中CCD实时采集到的不锈钢表面的激光光斑图样,采用COMSOL Multiphysic数值模拟软件,模拟了烧蚀过程中激光束的发散传播行为,并计算了光束发散角。结果表明:当激光重复频率为5kHz时,厚度为160μm的0Cr18Ni9不锈钢切缝和孔边缘被明显烧黑,切缝处晶粒明显长大,存在热影响区;烧蚀过程中,由飞秒激光超高功率密度所致的金属-空气混合等离子体使光束沿传播方向上发生散射,发散角在6°～10°之间。热影响区的存在和混合等离子体的行为是影响飞秒激光烧蚀0Cr18Ni9不锈钢精度的主要因素。     

高厚度薄膜-泡沫平面调制靶的飞秒激光微加工

 利用数值孔径为0.14的显微物镜聚焦中心波长800 nm、脉宽120 fs、重复频率1 kHz的飞秒激光,采用焦点逐线扫描等距下移方式,选取的入射平均功率为30 mW,加工速度为300 μm/s,对瑞利-泰勒(R-T)不稳定性实验靶用的厚度1.5 mm聚苯乙烯（PS）薄膜-聚4-甲基-1-戊烯（PMP）泡沫双层复合长条块体样品进行精确切割成型,并与纳秒激光切割情形对比。结果表明：利用飞秒激光微加工有效控制了切割区变形和材料分层,获得了整齐的切割边缘和平坦的切割面,样品最大切割深度超过800 μm。     

Femtosecond pulsed laser ablation of thin gold film

Laser micromachining on 1000 nm-thick gold film using femtosecond laser has been studied. The laser pulses that are used for this study are 400 nm in central wavelength, 150 fs in pulse duration, and the repetition rate is 1 kHz. Plano-concave lens with a focal length of 19 mm focuses the laser beam into a spot of 3 μm (1/e² diameter). The sample was translated at a linear speed of 400 μm/s during machining. Grooves were cut on gold thin film with laser pulses of various energies. The ablation depths were measured and plotted. There are two ablation regimes. In the first regime, the cutting is very shallow and the edges are free of molten material. While in the second regime, molten material appears and the cutting edges are contaminated. The results suggest that clean and precise microstructuring can be achieved with femtosecond pulsed laser by controlling the pulse energy in the first ablation regime.     

Fast femtosecond laser ablation for efficient cutting of sintered alumina substrates

Fast, accurate cutting of technical ceramics is a significant technological challenge because of these materials' typical high mechanical strength and thermal resistance. Femtosecond pulsed lasers offer significant promise for meeting this challenge. Femtosecond pulses can machine nearly any material with small kerf and little to no collateral damage to the surrounding material. The main drawback to femtosecond laser machining of ceramics is slow processing speed. In this work we report on the improvement of femtosecond laser cutting of sintered alumina substrates through optimisation of laser processing parameters. The femtosecond laser ablation thresholds for sintered alumina were measured using the diagonal scan method. Incubation effects were found to fit a defect accumulation model, with F_th,1=6.0 J/cm² (±0.3) and F_th,∞=2.5 J/cm² (±0.2). The focal length and depth, laser power, number of passes, and material translation speed were optimised for ablation speed and high quality. Optimal conditions of 500 mW power, 100 mm focal length, 2000 µm/s material translation speed, with 14 passes, produced complete cutting of the alumina substrate at an overall processing speed of 143 µm/s – more than 4 times faster than the maximum reported overall processing speed previously achieved by Wang et al. [1]. This process significantly increases processing speeds of alumina substrates, thereby reducing costs, making femtosecond laser machining a more viable option for industrial users.     

基于飞秒激光的光纤切割加工工艺研究

为了得到理想的光纤切割断面,利用飞秒激光对石英光纤材料进行切割微加工实验。研究激光功率、脉冲频率、扫描速度等加工参数与光纤切割断面质量间的关系,以寻求最理想的加工参数。最后在可调倾角光纤夹具的辅助下,很好地弥补加工过程中产生的端面倾斜角,得到垂直度高达89.56°的光纤切割断面。     

多脉冲飞秒激光对锗材料的烧蚀效应

 开展了脉宽为40 fs的不同数量激光脉冲对锗材料的烧蚀效应实验,采用扫描电镜、激光共聚焦显微镜等方法对不同数量的飞秒激光脉冲作用下锗材料表面烧蚀区进行了检测,并对作用后材料烧蚀形貌演化规律进行了分析,初步分析了锗材料烧蚀区周围形成的不同环区的形貌特征及成因,对各环区烧蚀形貌特征随激光作用脉冲数的增加而产生的形貌演化过程进行了观测。并给出单脉冲飞秒激光对锗材料的烧蚀阈值为1.2 J·cm^-2,采用激光共聚焦显微镜测得该阈值条件下单个飞秒激光脉冲对锗材料的烧蚀深度约为150 nm。     

Mechanisms of femtosecond laser nanosurgery of cells and tissues

We review recent advances in laser cell surgery, and investigate the working mechanisms of femtosecond laser nanoprocessing in biomaterials with oscillator pulses of 80-MHz repetition rate and with amplified pulses of 1-kHz repetition rate. Plasma formation in water, the evolution of the temperature distribution, thermoelastic stress generation, and stress-induced bubble formation are numerically simulated for NA=1.3, and the outcome is compared to experimental results. Mechanisms and the spatial resolution of femtosecond laser surgery are then compared to the features of continuous-wave (cw) microbeams. We find that free electrons are produced in a fairly large irradiance range below the optical breakdown threshold, with a deterministic relationship between free-electron density and irradiance. This provides a large ‘tuning range’ for the creation of spatially extremely confined chemical, thermal, and mechanical effects via free-electron generation. Dissection at 80-MHz repetition rate is performed in the low-density plasma regime at pulse energies well below the optical breakdown threshold and only slightly higher than used for nonlinear imaging. It is mediated by free-electron-induced chemical decomposition (bond breaking) in conjunction with multiphoton-induced chemistry, and hardly related to heating or thermoelastic stresses. When the energy is raised, accumulative heating occurs and long-lasting bubbles are produced by tissue dissociation into volatile fragments, which is usually unwanted. By contrast, dissection at 1-kHz repetition rate is performed using more than 10-fold larger pulse energies and relies on thermoelastically induced formation of minute transient cavities with lifetimes <100 ns. Both modes of femtosecond laser nanoprocessing can achieve a 2–3 fold better precision than cell surgery using cw irradiation, and enable manipulation at arbitrary locations. PACS 42.62.Be; 72.20.Jv     

PMP泡沫的飞秒激光烧蚀及切割方法

对密度为90 mg/cm3的PMP泡沫材料的飞秒激光烧蚀结果进行了分析,推导出该材料在脉宽50 fs、波长800 nm、重复频率为1000 Hz的飞秒激光作用下的蚀除阈值为0.91 J/cm2（100个激光脉冲）,获得了烧蚀直径分别随激光功率、脉冲数及聚焦物镜数值孔径的变化规律。相同飞秒激光加工系统下,对比了铜箔上获得的烧蚀形状,确定了PMP泡沫材料本身的多孔洞及其分布不均匀是造成烧蚀区域的形状不规则的重要因素。PMP泡沫在较高能量或是较长时间的飞秒激光作用下,烧蚀区域发生碳化的原因是由热作用引发的。提出了一种基于激光束耦合的飞秒激光切割厚度大于1 mm的薄膜-泡沫材料的方法,并获得了切割厚度大于1.5 mm、切割侧壁与光束光轴夹角小于5、切割面整洁的薄片。     

Femtosecond laser modification of living neuronal network

An all-wet femtosecond laser microprocessing technique was utilized for patterning and cutting functional network of living neuronal cells on a multi-electrode dish (MED). The neuronal cells cultured on a source substrate were transferred onto an electrode in a MED probe in solution by utilizing a femtosecond laser-induced impulsive force and a pattern of neuronal cells were formed on the MED probe. The cellular activity of the detached neurons was supported that neurites could be regenerated around the electrodes. As another processing method, the neurons stretching between electrodes were selectively cut by the direct femtosecond laser irradiation and the spontaneous electrical activity of the neuronal network was evaluated. While the spontaneous action potentials of neurons were synchronized before the cutting, the synchronization disappeared after the cutting, indicating that the neuronal network is locally disconnected by the laser cutting. The present method is applicable to artificial reconstruction of living neuronal network.     

Measurement of femtosecond laser-induced damage and ablation thresholds in dielectrics

The paper is focused on the importance of accurate determination of surface damage/ablation threshold of a dielectric material irradiated with femtosecond laser pulses. We show that different damage characterization techniques and data treatment procedures from a single experiment provide complementary physical results characterizing laser–matter interaction. We thus compare and discuss two regression techniques, well adapted to the measurement of laser ablation threshold, and a statistical approach giving the laser damage threshold and further information concerning the deterministic character of femtosecond damage. These two measurements are crucial for laser micromachining processes and high peak-power laser technology in general.     

高激光损伤阈值Ge-As-S硫系玻璃光纤及中红外超连续谱产生

测量了Ge-As-S系列硫系玻璃在中红外波段的飞秒激光损伤阈值,研究了它与玻璃化学组成的关系.基于优化的玻璃组成,采用棒管法制备了芯径为15μm的阶跃折射率非线性光纤.采用飞秒脉冲抽运光纤,研究了光纤中超连续谱(supercontinuum,SC)的产生特性.在研究的Ge-As-S硫系玻璃中,具有化学计量配比的Ge0....     

飞秒平顶光束经微透镜阵列在熔融石英中的成丝及其超连续辐射

实验研究了平顶激光光束经微透镜阵列在熔融石英中成丝的演化以及超连续辐射的产生,并进一步与高斯光束的成丝和超连续辐射进行了对比研究.分别对这两种光束的多丝传输进行了横向和纵向成像.结果表明,使用平顶光束可以获得更为均匀的多丝分布,成丝的起点也更为一致;尤其重要的是,相对于高斯光束,平顶光束可以使用更高的入射激光脉冲能量而不会造成介质的损伤,从而可以获得更高脉冲能量和更高转换效率的超连续辐射.     

Effect of femtosecond laser radiation on mammalian oocytes

Nucleolus-like bodies (NLBs) of mammalian oocytes are a convenient object for studying the effects of laser radiation on cellular organelles during laser surgery operations. NLBs in mouse germinal vesicle oocytes (GV oocytes) were subject to nanosurgery by means of tightly focused femtosecond laser pulses at near-infrared wavelength. The damage threshold of the NLB material was one-half orders of magnitude below the threshold for the water breakdown by femtosecond pulses. An incision of NLB material with submicron resolution was obtained at a threshold pulse energy. At the pulse energy one order of magnitude higher than the threshold level, significant deformation and rupture of NLBs were observed. Anisotropic deformations of the NLBs and the dynamics of their relaxation indicate the presence of granular structure in these organelles. Mechanical strain and the formation of cavitation and steam-gas bubbles in the place of impact of laser pulses can be described with the help of a model of the laser breakdown of medium.     

Experimental femtosecond laser photodisruption of rabbit sclera for minimally invasive laser sclerostomy: An in vitro study

Femtosecond laser technology, used as a minimally invasive tool in intrastromal refractive surgery, may also have potential as a useful instrument for glaucoma filtration surgery. The purpose of the present study was to evaluate the feasibility of minimally invasive laser sclerostomy by femtosecond laser photodisruption and seek the appropriate patterns of laser ablation and relevant laser parameters. A femtosecond laser (800 nm/50 fs/1 kHz), focused by a 0.1 numerical aperture (NA) objective lens, with different pulse energies and exposure times was applied to ablate hydrated rabbit sclera in vitro. The irradiated samples were examined by scanning electron microscopy (SEM). By moving a three-dimensional, computer-controlled translation stage to which the sample was attached, the femtosecond laser could produce three types of ablation patterns, including linear ablation, cylindrical aperture and rectangular cavity. With pulse energies ranging from 37.5 to 150 μJ, the linear lesions were consistently observed at the inner surface of sclera, whereas it failed to make any photodisruption if pulse energy was below the threshold value of 31.25 μJ, with the corresponding threshold intensity of 4.06×10¹⁴ W/cm². The depths of the linear lesions increased linearly with both pulse energy (37.5–150 μJ) and exposure time (0.1–0.4 s). Histological examination showed the incisions produced by femtosecond laser photodisruption had precise geometry and the edges were sharp and smooth, with no evidence of collateral damage to the surrounding tissue. Our results predict the potential application of femtosecond laser pulses in minimally invasive laser sclerostomy for glaucoma treatment.     

Mechanisms of femtosecond laser-induced breakdown and damage in MgO

Single-shot laser damage threshold of MgO for 40-986 fs, 800 nm laser pulses is reported. The pump-probe measurements with femtosecond pulses were carried out to investigate the time-resolved electronic excitation processes. A theoretical model including conduction band electrons (CBE) production and laser energy deposition was applied to discuss the roles of multiphoton ionization (MPI) and avalanche ionization in femtosecond laser-induced dielectric breakdown. The results indicate that avalanche ionization plays the dominant role in the femtosecond laser-induced breakdown in MgO near the damage threshold.     

Metal absorptivity in femtosecond pulsed laser ablation

In this paper, the effect of the absorptivity of metal on femtosecond pulsed laser ablation is investigated. The formulas for the absorptivity depending on target temperature are derived from Maxwell Equations and the Lambert-Beer’s law. Based on this, a new two-temperature model is proposed to describe the femtosecond pulsed laser ablation with metal. Then, using Au as an example, a finite difference method is employed to simulate the space-dependent and time-dependent absorptivity and the target temperature. The temperature evolution of our model is compared with the result obtained form the heat conduction model taking the absorptivity as constant. It is shown that the absorptivity plays an important role in the femtosecond pulsed laser ablation. The results of this paper are helpful in choosing the best technical parameters in femtosecond pulsed laser ablation.