The spontaneous emission of an atom is not a property of the atom only; it also depends on the local optical surroundings. The simplest demonstration of this effect was provided by the early experiments of Drexhage, who studied the emission rate of luminescent europium ions close to a mirror. It was found that while the spectral distribution of the emission remained constant, the emission rate was dependent on the position of the Eu3+ ions relative to the mirror. This effect is due to interference of the optical modes incident to and reflected at the mirror. Since then, the modified spontaneous emission of atoms in cavities has been studied extensively. More recently, the control of spontaneous emission in solid-state systems has become of great interest because it enables the tailoring of the emission properties of optical materials. It was shown how the spontaneous-emission rate of optical probe ions or dyes inside dielectric films is modified by the presence of a dielectric interface, in a dielectric multilayer, or a microcavity. The dependence of the decay rate on the optical surroundings in these one-dimensional systems can be described in terms of Fermi's “golden rule,” which states that the decay rate is proportional to the local optical density of states (DOS). The spatial variation in the DOS is due to the interference of optical modes reflected and refracted at the dielectric interface(s).
原子的自发辐射并不仅仅是原子本身的属性;它还依赖于局部的光环境。这种效应最简单的演示是由Drexhage的早期实验提供的,他研究了发光的铕离子在镜子附近的发射率。研究发现,虽然发射的光谱分布保持不变,但发射率却依赖于铕离子相对于镜子的位置。这种效应是由于入射到镜子上并从镜子反射的光学模式的干涉造成的。自那时起,人们广泛研究了腔中原子修改后的自发辐射。最近,控制固态系统中的自发辐射已经引起了极大的兴趣,因为它能够定制光学材料的发射特性。已经展示了光学探针离子或染料在介电膜内的自发发射率如何通过介电界面、介电多层膜或微腔的存在而发生变化。这些一维系统中衰减率对光学环境依赖性可以用费米“黄金规则”来描述,该规则指出衰减率与局部光学态密度(DOS)成正比。DOS的空间变化是由于在介电界面反射和折射的光学模式的干涉造成的。