Nonlinear optical phenomena in silicon such as self-focusing and multi-photon absorption are strongly dependent on the wavelength, energy, and duration of the exciting pulse, especially for wavelengths ${\gt}{{2}}\;{\rm{\unicode{x00B5}{\rm m}}}$. We investigate the sub-surface modification of silicon using ultra-short pulsed lasers at wavelengths in the range of 1950–2400 nm, at a pulse duration between 2 and 10 ps and pulse energy varying from 1 µJ to 1 mJ. We perform numerical simulations and experiments using fiber-based lasers built in-house that operate in this wavelength range for the surface and sub-surface processing of Si-wafers. The results are compared to the literature data at 1550 nm. Due to a dip in the nonlinear absorption spectrum and a peak in the spectrum of the third-order nonlinearity, the wavelengths between 2000 and 2200 nm prove to be more favorable for creating sub-surface modifications in silicon. This is the case even though those wavelengths do not allow as tight focusing as those at 1550 nm. This is compensated for by an increased self-focusing due to the nonlinear Kerr-effect around 2100 nm at high light intensities, characteristic for ultra-short pulses.

中文翻译：

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使用2 µm以上的超短脉冲激光对硅进行亚表面改性

硅中的非线性光学现象，例如自聚焦和多光子吸收，在很大程度上取决于激发脉冲的波长，能量和持续时间，尤其是对于波长{{\ gt} {{2}} \ ;; {\ rm { \ unicode {x00B5} {\ rm m}}}​​ $。我们研究了使用超短脉冲激光在1950–2400 nm范围内，脉冲持续时间为2到10 ps和脉冲能量在1 µJ至1 mJ之间变化的情况下对硅进行的表面下改性。我们使用内部制造的基于光纤的激光器进行数值模拟和实验，该激光器在此波长范围内运行，用于硅晶片的表面和亚表面处理。将结果与1550 nm处的文献数据进行比较。由于非线性吸收光谱的下降和三阶非线性光谱的峰值，在2000和2200 nm之间的波长证明更有利于在硅中产生亚表面改性。即使这些波长不允许像1550 nm波长那样紧密聚焦，也是如此。