Institute of Optics and Atomic Physics, Technical University of Berlin , Strasse des 17. Juni 135, 10623 Berlin, Germany.
Research Institute for Physical Chemical Problems of Belarusian State University , 220006, Minsk, Belarus.
Nano Lett. 2017 Oct 11;17(10):6321-6329. doi: 10.1021/acs.nanolett.7b03052. Epub 2017 Sep 18.
We show that two-photon absorption (TPA) is highly anisotropic in CdSe nanoplatelets, thus promoting them as a new class of directional two-photon absorbers with large cross sections. Comparing two-dimensional k-space spectroscopic measurements of the one-photon and two-photon excitation of an oriented monolayer of platelets, it is revealed that TPA into the continuum is a directional phenomenon. This is in contrast to one-photon absorption. The observed directional TPA is shown to be related to fundamental band anisotropies of zincblende CdSe and the ultrastrong anisotropic confinement. We recover the internal transition dipole distribution and find that this directionality arises from the intrinsic directionality of the underlying Bloch and envelope functions of the states involved. We note that the photoemission from the CdSe platelets is highly anisotropic following either one- or two-photon excitation. Given the directionality and high TPA cross-section of these platelets, they may, for example, find employment as efficient logic AND elements in integrated photonic devices, or directional photon converters.
我们证明了在 CdSe 纳米板中双光子吸收（TPA）具有高度各向异性，因此将其作为具有大截面的新型定向双光子吸收体。通过比较各向同性单层板的单光子和双光子激发的二维 k 空间光谱测量，揭示了连续体中的 TPA 是一种定向现象。这与单光子吸收相反。观察到的定向 TPA 与闪锌矿 CdSe 的基本带各向异性和超强各向异性限制有关。我们恢复了内部跃迁偶极子分布，并发现这种方向性源于所涉及的状态的基本布洛赫和包络函数的固有方向性。我们注意到，无论是单光子还是双光子激发，CdSe 纳米板的光发射都具有各向异性。鉴于这些纳米板的方向性和高 TPA 截面，它们可能例如在集成光子器件中用作高效逻辑与元件，或定向光子转换器。
