Transient absorption is a very powerful observable in attosecond experiments on atoms, molecules and solids and is frequently used in experiments employing phase-locked few-cycle infrared and XUV laser pulses derived from high harmonic generation. We show numerically and analytically that in non-centrosymmetric systems, such as many polyatomic molecules, which-way interference enabled by the lack of parity conservation leads to new spectral absorption features, which directly reveal the laser electric field. The extension of attosecond transient absorption spectroscopy (ATAS) to such targets hence becomes sensitive to global and local inversion symmetry. We anticipate that ATAS will find new applications in non-centrosymmetric systems, in which the carrier-to-envelope phase of the infrared pulse becomes a relevant parameter and in which the orientation of the sample and the electronic symmetry of the molecule can be addressed.

中文翻译：

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无反对称的亚秒瞬态吸收光谱

瞬态吸收在原子，分子和固体的原子秒实验中是非常强大的观测值，并且经常用于采用由高谐波产生衍生的锁相的少周期红外和XUV激光脉冲的实验中。我们通过数值和分析方法表明，在非中心对称系统（例如许多多原子分子）中，由于缺乏奇偶性守恒而导致的单向干涉会导致新的光谱吸收特征，从而直接揭示了激光电场。因此，将阿秒瞬态吸收光谱（ATAS）扩展到此类目标变得对全局和局部反演对称性敏感。我们预计ATAS将在非中心对称系统中找到新的应用，