Liang Jinyang, Zhu Liren, Wang Lihong V
1Caltech Optical Imaging Laboratory, Andrew and Peggy Cherng Department of Medical Engineering, Department of Electrical Engineering, California Institute of Technology, 1200 East California Boulevard, Mail Code 138-78, Pasadena, CA 91125 USA.
2Present Address: Centre Énergie Matériaux Télécommunications, Institut National de la Recherche Scientifique, 1650 Boulevard Lionel-Boulet, Varennes, QC J3X1S2 Canada.
Light Sci Appl. 2018 Aug 8;7:42. doi: 10.1038/s41377-018-0044-7. eCollection 2018.
While the concept of focusing usually applies to the spatial domain, it is equally applicable to the time domain. Real-time imaging of temporal focusing of single ultrashort laser pulses is of great significance in exploring the physics of the space-time duality and finding diverse applications. The drastic changes in the width and intensity of an ultrashort laser pulse during temporal focusing impose a requirement for femtosecond-level exposure to capture the instantaneous light patterns generated in this exquisite phenomenon. Thus far, established ultrafast imaging techniques either struggle to reach the desired exposure time or require repeatable measurements. We have developed single-shot 10-trillion-frame-per-second compressed ultrafast photography (T-CUP), which passively captures dynamic events with 100-fs frame intervals in a single camera exposure. The synergy between compressed sensing and the Radon transformation empowers T-CUP to significantly reduce the number of projections needed for reconstructing a high-quality three-dimensional spatiotemporal datacube. As the only currently available real-time, passive imaging modality with a femtosecond exposure time, T-CUP was used to record the first-ever movie of non-repeatable temporal focusing of a single ultrashort laser pulse in a dynamic scattering medium. T-CUP's unprecedented ability to clearly reveal the complex evolution in the shape, intensity, and width of a temporally focused pulse in a single measurement paves the way for single-shot characterization of ultrashort pulses, experimental investigation of nonlinear light-matter interactions, and real-time wavefront engineering for deep-tissue light focusing.
虽然聚焦的概念通常适用于空间域，但它同样适用于时间域。对单个超短激光脉冲的时间聚焦进行实时成像，对于探索时空对偶性的物理原理以及寻找多种应用具有重要意义。超短激光脉冲在时间聚焦过程中宽度和强度的急剧变化，要求曝光时间达到飞秒级别，以捕捉这一精妙现象中产生的瞬间光图案。到目前为止，现有的超快成像技术要么难以达到所需的曝光时间，要么需要进行可重复测量。我们开发了单帧每秒10万亿帧的压缩超快摄影技术（T-CUP），它能在单次相机曝光中以100飞秒的帧间隔被动捕捉动态事件。压缩感知与拉东变换之间的协同作用使T-CUP能够显著减少重建高质量三维时空数据立方体所需的投影数量。作为目前唯一可用的具有飞秒曝光时间的实时、被动成像模式，T-CUP被用于记录单个超短激光脉冲在动态散射介质中不可重复的时间聚焦的首部影片。T-CUP在单次测量中清晰揭示时间聚焦脉冲的形状、强度和宽度复杂演变的前所未有的能力，为超短脉冲的单帧表征、非线性光与物质相互作用的实验研究以及用于深层组织光聚焦的实时波前工程铺平了道路。
