Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States.
Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, United States.
J Am Chem Soc. 2021 Oct 20;143(41):16930-16934. doi: 10.1021/jacs.1c09728. Epub 2021 Oct 6.
Entangled two-photon absorption (ETPA) is known to create photoinduced transitions with extremely low light intensity, reducing the risk of phototoxicity compared to classical two-photon absorption. Previous works have predicted the ETPA cross-section, σ, to vary inversely with the product of entanglement time () and entanglement area (), i.e., σ ∼ 1/. The decreasing σ with increasing has limited ETPA to fs-scale , while ETPA applications for ps-scale spectroscopy have been unexplored. However, we show that spectral-spatial coupling, which reduces as the SPDC bandwidth (σ) decreases, plays a significant role in determining σ when > ∼100 fs. We experimentally measured σ for zinc tetraphenylporphyrin at several σ values. For type-I ETPA, σ increases as σ decreases down to 0.1 ps. For type-II SPDC, σ is constant for a wide range of σ. With a theoretical analysis of the data, the maximum type-I σ would occur at σ = 0.1 ps ( = 10 ps). At this maximum, σ is 1 order of magnitude larger than fs-scale σ and 3 orders of magnitude larger than previous predictions of ps-scale σ. By utilizing this spectral-spatial coupling, narrowband type-I ETPA provides a new opportunity to increase the efficiency of measuring nonlinear optical signals and to control photochemical reactions requiring ps temporal precision.
纠缠双光子吸收（ETPA）已知可在极低光强下产生光诱导跃迁，与经典双光子吸收相比，降低了光毒性的风险。先前的工作预测纠缠时间（）和纠缠面积（）的乘积会使 ETPA 截面（）反向变化，即 σ∼1/。随着的增加而减小的 σ 限制了 ETPA 到 fs 尺度，而 ps 尺度光谱学的 ETPA 应用尚未得到探索。然而，我们表明，光谱-空间耦合会随着 SPDC 带宽（）的减小而减小，当 >∼100 fs 时，它在确定 σ 方面起着重要作用。我们在几个 σ 值下测量了锌四苯基卟啉的 σ。对于 I 型 ETPA，随着 σ 从 0.1 ps 减小，σ 增加。对于 II 型 SPDC，在很宽的 σ 范围内，σ 是恒定的。通过对数据的理论分析，I 型 σ 的最大值将出现在 σ=0.1 ps（=10 ps）处。在此最大值处，σ 比 fs 尺度 σ 大 1 个数量级，比 ps 尺度 σ 的先前预测大 3 个数量级。通过利用这种光谱-空间耦合，窄带 I 型 ETPA 为提高测量非线性光学信号的效率和控制需要 ps 时间精度的光化学反应提供了新的机会。
