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Intense Femtosecond Pulse Propagation with Applications

机译：强飞秒脉冲传播及其应用

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The fundamental physics of high-field laser-matter interactions has driven ultrashort pulse generation to achieve record power densities of 10~(22) Watts per cm~2 in focal spot sizes (FWHM) of 0.8 μm~1. These enormous fields are generated by compressing longer, high energy pulses to ever shorter lengths using so-called CPA compressors. Great care has to be taken to achieve such record power densities by controlling the spatio-temporal shape during pulse compression. Despite these remarkable experimental achievements, there have been relatively few developments on the theoretical side to derive realistic physical optical material models coupled to sophisticated E.M propagators. Many of the theoretical analysis tools developed in this emerging field of extreme nonlinear optics are restricted to oversimplified 1D models that completely ignore the complex vector spatio-temporal couplings occurring within such small nonlinear interaction volumes. The advent of these high power ultra-short pulsed laser systems has opened up a whole new vista of applications and computational challenges. The applications space spans relatively short propagation lengths of centimeters to meters to a target up to many kilometers in atmospheric propagation studies. The high local field intensities generated within the pulse can potentially lead to electromagnetic carrier wave shocking so it becomes necessary to fully resolve the optical carrier wave within the 3D propagating pulse envelope. High local field intensities also lead to an explosive growth of the white-light supercontinuum spectrum and the intensities of even remote spectral components can be high enough to generate nonlinear coupling to the host material. For this reason, spectrally local models of light-matter coupling are expected to fail. In this paper, we will present a fully carrier-resolved E.M. propagator that allows for few meter long propagation lengths while fully resolving the optical carrier wave. Our applications focus will be on the relatively low intensity regime where critical self-focusing collapse in air or water can lead to very strong non-paraxial ultra-broadband excitations. One reason for this restriction is that we do not yet have computationally feasible robust physical models for ultra-broadband excitation of materials where nonlinear dispersion and absorption become dominant. The propagation of terawatt femtosecond duration pulses in the atmosphere can be qualitatively captured by physical models that include reliable linear dispersion/absorption while treating the nonlinear terms as spectrally local. We will review some recent experimental results by the German-Franco Teramobile team on atmospheric propagation, penetration through obscurants and remote laser induced breakdown spectroscopy. As a second application example will address the issue of strongly non-paraxial spectral superbroadening of femtosecond pulses while propagating in water - these latter nonlinear interactions generate so-called nonlinear X- and O-waves depending on the optical carrier wavelength of the initial pulse.
机译：高场激光与物质相互作用的基本物理学驱使超短脉冲产生，以在0.8μm〜1的焦点尺寸（FWHM）中达到10〜（22）W / cm〜2的记录功率密度。这些巨大的磁场是通过使用所谓的CPA压缩机将更长的高能量脉冲压缩到越来越短的长度而产生的。必须通过控制脉冲压缩期间的时空形状来达到这样的记录功率密度。尽管取得了这些卓越的实验成就，但在理论上相对较少的开发可以得出与复杂的E.M传播器耦合的逼真的物理光学材料模型。在极端非线性光学这个新兴领域中开发的许多理论分析工具仅限于过于简化的一维模型，这些模型完全忽略了在如此小的非线性相互作用体积内发生的复杂矢量时空耦合。这些高功率超短脉冲激光系统的出现开辟了应用和计算挑战的全新视野。在大气传播研究中，应用空间跨越了从几厘米到几米的相对短的传播长度，达到了长达数千米的目标。脉冲内产生的高局部场强度可能会导致电磁载波震荡，因此有必要完全解析3D传播脉冲包络内的光学载波。高的局部场强还会导致白光超连续谱的爆炸性增长，并且即使是远程光谱分量的强度也可能足够高，以生成与主体材料的非线性耦合。由于这个原因，预期的光物质耦合的光谱局部模型将失败。在本文中，我们将介绍一种完全由载波解析的E.M.传播器，该传播器在完全解析光学载波的同时允许几米长的传播长度。我们的应用重点将放在相对低强度的区域，在该区域中，空气或水中的严重自聚焦崩溃会导致非常强的非傍轴超宽带激发。出现这种限制的原因之一是，对于非线性色散和吸收占主导地位的材料的超宽带激发，我们还没有在计算上可行的稳健物理模型。兆瓦飞秒持续时间脉冲在大气中的传播可以通过物理模型进行定性捕获，这些物理模型包括可靠的线性色散/吸收，同时将非线性项视为频谱局部的。我们将回顾德国-弗朗哥·特拉莫比尔（Feramobile）小组最近在大气传播，透过遮盖剂的穿透以及远程激光诱导击穿光谱学方面的一些实验结果。作为第二个应用示例，它将解决飞秒脉冲在水中传播时发生的强烈非傍轴光谱超展宽的问题-后者的非线性相互作用会根据初始脉冲的光学载波波长生成所谓的非线性X波和O波。

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