Femtosecond-laser-produced low-density plasmas in transparent biological media: a tool for the creation of chemical, thermal, and thermomechanical effects below the optical breakdown threshold
Femtosecond-laser-produced low-density plasmas in transparent biological media: a tool for the creation of chemical, thermal, and thermomechanical effects below the optical breakdown threshold
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飞秒激光在透明生物介质中产生低密度等离子体：一种在光学击穿阈值以下产生化学、热和热机械效应的工具
DOI：
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
G. Paltauf
中科院分区：
文献类型：
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作者：
A. Vogel;J. Noack;G. Huettmann;G. Paltauf
水介质中飞秒光击穿的辐照度阈值约为1.0 × 1013 W cm-2。在击穿阈值时，产生了自由电子密度约为1021 cm-3的等离子体，击穿区的能量密度足够高，可以导致实验观察到的气泡的形成。我们以前发现，自由电子密度<1021 cm-3的等离子体也形成在一个相当大的辐照度低于击穿阈值的范围。本研究调查的化学，热，和热机械效应产生的这些低密度等离子体。我们使用的速率方程模型考虑多光子电离和产生这些低密度等离子体。我们使用一个速率方程模型，考虑多光子电离和雪崩电离数值模拟的自由电子密度的时间演化过程中的激光脉冲对于一个给定的辐照度，并计算的自由电子密度和体积能量密度的辐照度依赖于激光脉冲结束时达到。然后，由每个激光脉冲产生的能量密度的值用于计算在施加单个激光脉冲和一系列脉冲之后聚焦区域中的温度分布。最后，温度计算的结果产生用于计算在低密度等离子体的形成期间产生的热弹性应力的起始点。我们发现，特别是对于短波长，一个大的“调谐范围”存在的空间极其有限的化学，热和机械效应，通过非线性吸收，通过自由电子生成的创建。光化学效应在辐照度范围的下端占主导地位，而在上端，它们与热效应混合并由热弹性应力修改。在击穿阈值以上，空泡的形成部分破坏了空间约束，激光诱导效应变得更具破坏性。我们的模拟结果表明，最近由其他研究人员证明的细胞内结构和核内染色体解剖的高度局部化消融可能是由自由电子诱导的化学键断裂介导的，与加热或热弹性应力无关。我们的结论是，低于光学击穿阈值的低密度等离子体可以是一个通用的工具，用于操纵透明的生物介质和其他透明材料。（例如，在大块玻璃中产生光波导）。然而，低密度等离子体也可能是多光子显微镜和高次谐波成像中的潜在危险。
The irradiance threshold for femtosecond optical breakdown in aqueous media is approximately equals 1.0x1013W cm-2. At the breakdown threshold, a plasma with a free electron density of about 1021cm-3 is generated, and the energy density in the breakdown region is sufficiently high to cause the formation of a bubble which can be experimentally observed. We found previously that plasmas with a free electron density <1021cm-3 are formed also in a fairly large irradiance range below the breakdown threshold. The present study investigates the chemical, thermal, and thermomechanical effects produced by these low-density plasmas. We use a rate equation model considering multiphoton ionization and produced by these low-density plasmas. We use a rate equation model considering multiphoton ionization and avalanche ionization to numerically simulate the temporal evolution of the free electron density during the laser pulse for a given irradiance, and to calculate the irradiance dependence of the free-electron density and volumetric energy density reached at the end of the laser pulse. The value of the energy density created by each laser pulse is then used to calculate the temperature distribution in the focal region after application of a single laser pulse and of series of pulses. The results of the temperature calculations yield, finally, the starting point for calculations of the thermoelastic stresses that are generated during the formation of the low-density plasmas. We found that, particularly for short wavelengths, a large 'tuning range' exists for the creation of spatially extremely confined chemical, thermal and mechanical effects via free electron generation through nonlinear absorption. Photochemical effects dominate at the lower end of this irradiance range, whereas at the upper end they are mixed with thermal effects and modified by thermoelastic stresses. Above the breakdown threshold, the spatial confinement is partly destroyed by cavitation bubble formation, and the laser-induced effects become more disruptive. Our simulations revealed that the highly localized ablation of intracellular structures and intranuclear chromosome dissection recently demonstrated by other researchers are probably mediated by free-electron- induced chemical bond breaking and not related to heating or thermoelastic stresses. We conclude that low density plasmas below the optical breakdown threshold can be a versatile tool for the manipulation of transparent biological media and other transparent materials. (enabling, e.g., the generation of optical waveguides in bulk glass). Low density plasmas may, however, also be a potential hazard in multiphoton microscopy and higher harmonic imaging.
激光微束作为细胞生物学的工具。
DOI：
10.1016/s0074-7696(08)60507-0
发表时间：
1991
期刊：
International review of cytology
影响因子：
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作者：
Berns,MW;Wright,WH;WiegandSteubing,R
通讯作者：
WiegandSteubing,R