Parzuchowski Kristen M, Mazurek Michael D, Camp Charles H, Stevens Martin J, Jimenez Ralph
JILA, University of Colorado Boulder, Boulder, Colorado 80309, United States.
Department of Physics, University of Colorado Boulder, Boulder, Colorado 80309, United States.
ACS Photonics. 2025 Mar 7;12(3):1470-1479. doi: 10.1021/acsphotonics.4c02076. eCollection 2025 Mar 19.
We introduce a toluene-filled fiber platform for two-photon absorption measurements. By confining both the light and molecular sample inside the 5 μm hollow core of the fiber, we increase the distance over which the nonlinear light-matter interaction occurs. With only a 7.3 nL excitation volume, we measure classical two-photon absorption (C2PA) at an average laser power as low as 1.75 nW, which is a 45-fold improvement over a conventional free-space technique. We use this platform to attempt to measure entangled two-photon absorption (E2PA), a process with a limited regime where the quantum advantage is large. This regime arises due to a crossover from linear to quadratic scaling with photon flux as photon flux is increased. Recently, several teams of researchers have reported that E2PA cross-sections are much smaller than previously claimed. As a result, the linear scaling dominates at photon fluxes so low that it is extremely difficult or impossible to measure using conventional free-space techniques. In this report, we implement the first E2PA measurement using a waveguide. We see no evidence of E2PA, and we set an upper bound on the cross-section consistent with these recent reports.
我们介绍了一种用于双光子吸收测量的填充甲苯的光纤平台。通过将光和分子样品都限制在光纤5μm的空心芯内，我们增加了非线性光与物质相互作用发生的距离。仅用7.3 nL的激发体积，我们就能在低至1.75 nW的平均激光功率下测量经典双光子吸收（C2PA），这比传统的自由空间技术提高了45倍。我们使用这个平台尝试测量纠缠双光子吸收（E2PA），这是一个量子优势较大但范围有限的过程。随着光子通量增加，该范围源于从线性到二次方比例的转变。最近，几个研究团队报告称，E2PA截面比之前声称的要小得多。因此，在光子通量非常低以至于使用传统自由空间技术极难或无法测量的情况下，线性比例占主导。在本报告中，我们首次使用波导进行了E2PA测量。我们没有发现E2PA的证据，并根据这些最新报告设定了截面的上限。
