飞秒脉冲laser辐照固体锡靶的离子分布和烧蚀深度测量
Ion distribution and ablation depth measurements of a fs-ps laser-irradiated solid tin target
摘要：
研究了800纳米波长的激光对固体锡表面的烧蚀，其脉冲长度范围为500 fs ~ 4.5 ps，能量密度范围为0.9 ~ 22 J/cm ^2。采用高数值孔径光学显微镜获得的烧蚀深度和体积，而离子产额和能量分布是从一组法拉第杯设置在不同的角度。我们发现，增加脉冲长度的离子产额略有增加，而烧蚀深度略有下降。消融体积作为脉冲长度的函数保持恒定。烧蚀深度遵循两个区域的对数依赖的注量，与现有的文献和理论。在所研究的注量范围内，离子产额角分布在低注量下沿靶法线方向出现尖峰，但随着注量的增加而迅速加宽。总的电离分数单调增加的注量为5-6%的最大值，这是大大低于纳秒脉冲消融获得的典型的电离分数。在测量不确定度范围内，离子的角分布不依赖于激光脉冲长度。这些结果是特别感兴趣的可能利用飞秒激光系统在等离子体源的极紫外光纳米光刻。
英文摘要：
The ablation of solid tin surfaces by an 800-nanometer-wavelength laser is studied for a pulse length range from 500 fs to 4.5 ps and a fluence range spanning 0.9 to 22 J/cm^2. The ablation depth and volume are obtained employing a high-numerical-aperture optical microscope, while the ion yield and energy distributions are obtained from a set of Faraday cups set up under various angles. We found a slight increase of the ion yield for an increasing pulse length, while the ablation depth is slightly decreasing. The ablation volume remained constant as a function of pulse length. The ablation depth follows a two-region logarithmic dependence on the fluence, in agreement with the available literature and theory. In the examined fluence range, the ion yield angular distribution is sharply peaked along the target normal at low fluences but rapidly broadens with increasing fluence. The total ionization fraction increases monotonically with fluence to a 5-6% maximum, which is substantially lower than the typical ionization fractions obtained with nanosecond-pulse ablation. The angular distribution of the ions does not depend on the laser pulse length within the measurement uncertainty. These results are of particular interest for the possible utilization of fs-ps laser systems in plasma sources of extreme ultraviolet light for nanolithography.
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