Brechbühler Raphael, Vonk Sander J W, Aellen Marianne, Lassaline Nolan, Keitel Robert C, Cocina Ario, Rossinelli Aurelio A, Rabouw Freddy T, Norris David J
Optical Materials Engineering Laboratory, Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland.
Debye Institute for Nanomaterials Science, Utrecht University, 3584 CC Utrecht, The Netherlands.
ACS Nano. 2021 Jun 22;15(6):9935-9944. doi: 10.1021/acsnano.1c01338. Epub 2021 May 24.
Plasmonic modes in optical cavities can be amplified through stimulated emission. Using this effect, plasmonic lasers can potentially provide chip-integrated sources of coherent surface plasmon polaritons (SPPs). However, while plasmonic lasers have been experimentally demonstrated, they have not generated propagating plasmons as their primary output signal. Instead, plasmonic lasers typically involve significant emission of free-space photons that are intentionally outcoupled from the cavity by Bragg diffraction or that leak from reflector edges due to uncontrolled scattering. Here, we report a simple cavity design that allows for straightforward extraction of the lasing mode as SPPs while minimizing photon leakage. We achieve plasmonic lasing in 10-μm-long distributed-feedback cavities consisting of a Ag surface periodically patterned with ridges coated by a thin layer of colloidal semiconductor nanoplatelets as the gain material. The diffraction to free-space photons from cavities designed with second-order feedback allows a direct experimental examination of the lasing-mode profile in real- and momentum-space, in good agreement with coupled-wave theory. In contrast, we demonstrate that first-order-feedback cavities remain "dark" above the lasing threshold and the output signal leaves the cavity as propagating SPPs, highlighting the potential of such lasers as on-chip sources of plasmons.
光学腔中的表面等离子体激元模式可通过受激辐射得到放大。利用这一效应，表面等离子体激元激光器有潜力提供芯片集成的相干表面等离子体激元（SPP）源。然而，尽管表面等离子体激元激光器已通过实验得到证明，但它们尚未产生传播的表面等离子体激元作为其主要输出信号。相反，表面等离子体激元激光器通常会产生大量自由空间光子的发射，这些光子要么通过布拉格衍射有意地从腔中外耦合出来，要么由于不受控制的散射从反射器边缘泄漏。在此，我们报告了一种简单的腔设计，它能够在最小化光子泄漏的同时，将激射模式直接提取为表面等离子体激元。我们在由银表面构成的10微米长的分布反馈腔中实现了表面等离子体激元激射，该银表面周期性地刻有脊状图案，并涂覆有一层作为增益材料的胶体半导体纳米片。采用二阶反馈设计的腔向自由空间光子的衍射，使得能够在实空间和动量空间中对激射模式轮廓进行直接的实验检测，这与耦合波理论高度吻合。相比之下，我们证明了一阶反馈腔在激射阈值以上保持“暗态”，并且输出信号以传播的表面等离子体激元形式离开腔，这突出了此类激光器作为片上表面等离子体激元源的潜力。
