Despite the wide employment of transient absorption spectroscopy in capturing fast-evolving dynamics, the experiments lack further exploration of macroscopic effects beyond the single-atom response. Here, the absorbance of Rb atoms excited and coupled by two near-infrared pulses with a variable interpulse delay is studied both experimentally and theoretically, from the limit of a dilute-gas medium into high-density cases. Our results reveal that with increasing atomic density, the absorption lines are broadened with substructures emerging therein. However, the spectral evolutions are rather distinctive for positive and negative time delays, pointing toward different mechanisms behind them. As a distinguishing characteristic of the V -type levels, delay-dependent oscillations are entwined and complicate the resulting profiles considerably. The obtained intensity- and density-controlled line shapes are well reproduced based on the density matrix theory with the inclusion of ...

中文翻译：

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V型三能级系统中的宏观瞬态吸收

尽管在吸收快速发展的动力学中广泛采用了瞬态吸收光谱法，但该实验缺乏对单原子响应以外的宏观影响的进一步探索。在这里，从稀气体介质的极限到高密度的情况，从实验和理论上研究了由两个具有可变脉冲间延迟的近红外脉冲激发并耦合的Rb原子的吸光度。我们的结果表明，随着原子密度的增加，吸收线变宽，其中出现了子结构。但是，正向和负向时延的频谱演化都非常独特，指向它们背后的不同机制。作为V型能级的显着特征，与时延有关的振荡纠缠在一起，并使所得的分布相当复杂。