A robust approach for acquiring background-free, multitransition absorption spectra under single-laser-shot conditions is demonstrated using broadband, ultrashort laser pulses. This technique—referred to as time-resolved optically gated absorption (TOGA)—exploits the inherent differences in timescales between broadband, femtosecond-duration light sources and the longer-duration responses of narrowband atomic or molecular absorption features. An optical temporal gate, based on frequency mixing via sum-frequency generation or difference-frequency generation, is used to isolate these long-lived time-domain absorption features from the ultrashort component associated with the broadband absorption light source. A proof-of-principle demonstration of TOGA is provided using atomic Rb as an absorbing medium. Application of this technique toward single-laser-shot simultaneous detection of hydroxyl radical concentration and the corresponding local temperature is also demonstrated in a reacting flow. These results indicate that TOGA can provide spectrally resolved, broadband, background-free absorption measurements at laser-source repetition rates.

中文翻译：

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宽带，无背景，单激光吸收

使用宽带超短激光脉冲，展示了一种在单次激光照射条件下获取无背景，多跃迁吸收光谱的可靠方法。这项技术称为时间分辨的光学门控吸收（TOGA），它在宽带，飞秒持续时间的光源与窄带原子或分子吸收特征的较长持续时间的响应之间，揭示了时间尺度上的固有差异。基于通过和频产生或差频产生的频率混合的光学时间门用于将这些长时域吸收特征与与宽带吸收光源相关的超短分量隔离开。使用原子Rb作为吸收介质提供了TOGA的原理证明。在反应流中也证明了该技术在单次激光同时检测羟基自由基浓度和相应的局部温度中的应用。这些结果表明，TOGA可以以激光源重复频率提供光谱分辨的，宽带的，无背景的吸收测量值。