Arnold Nikita, Hrelescu Calin, Klar Thomas A
Institute of Applied Physics Johannes Kepler University Linz Altenbergerstraße 694040 Linz Austria; Soft Matter Physics Johannes Kepler University Linz Altenbergerstraße 694040 Linz Austria.
Institute of Applied Physics Johannes Kepler University Linz Altenbergerstraße 69 4040 Linz Austria.
Ann Phys. 2016 Apr;528(3-4):295-306. doi: 10.1002/andp.201500318. Epub 2015 Dec 7.
It is known (yet often ignored) from quantum mechanical or energetic considerations, that the threshold gain of the quasi-static spaser depends only on the dielectric functions of the metal and the gain material. Here, we derive this result from the purely classical electromagnetic scattering framework. This is of great importance, because electrodynamic modelling is far simpler than quantum mechanical one. The influence of the material dispersion and spaser geometry are clearly separated; the latter influences the threshold gain only indirectly, defining the resonant wavelength. We show that the threshold gain has a minimum as a function of wavelength. A variation of nanoparticle shape, composition, or spasing mode may shift the plasmonic resonance to this optimal wavelength, but it cannot overcome the material-imposed minimal gain. Furthermore, retardation is included straightforwardly into our framework; and the global spectral gain minimum persists beyond the quasi-static limit. We illustrate this with two examples of widely used geometries: Silver spheroids and spherical shells embedded in and filled with gain materials.
从量子力学或能量学的角度来看，准静态受激辐射放大（spaser）的阈值增益仅取决于金属和增益材料的介电函数，这是已知的（但常常被忽视）。在此，我们从纯经典电磁散射框架中推导出这一结果。这一点非常重要，因为电动力学建模比量子力学建模要简单得多。材料色散和spaser几何结构的影响被清晰地分开；后者仅间接影响阈值增益，确定共振波长。我们表明，阈值增益作为波长的函数存在最小值。纳米颗粒形状、组成或间距模式的变化可能会将等离子体共振转移到这个最佳波长，但无法克服材料所施加的最小增益。此外，延迟被直接纳入我们的框架；并且全局光谱增益最小值在准静态极限之外仍然存在。我们用两种广泛使用的几何结构示例来说明这一点：嵌入并填充增益材料的银椭球体和球壳。
