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arXiv 2109.14784physics.optics
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有增益介质时菲涅耳反射和透射的理论分析

Theoretical analysis of Fresnel reflection and transmission in the presence of gain media

Masud Mansuripur, Per K. Jakobsen

摘要:

当单色电磁平面波到达其透明主体(即,入射介质)和放大(或增益)第二介质,入射光束分裂成反射波和透射波。一般来说,存在与透射光束的k向量有关的符号模糊性,这需要在开始时决定透射光束在从界面后退时是应该增长还是衰减。在从高折射率的电介质到低折射率的增益介质的大角度入射的上下文中,已经提出并最突出地解决了这个问题。这里,传输的k矢量的相关符号确定增益介质内的类倏逝波是指数增长还是远离界面衰减。我们研究这一点和相关的问题,在一个更一般的设置,入射光束被视为一个有限持续时间的波包,其足迹在界面平面有一个有限的宽度。将考虑从有限厚度增益板反射和透射的情况以及与半无限增益介质相关的情况。我们的入射波包的时空谱的宽度要求我们开发一个通用的策略来决定进入增益介质的所有k向量的符号。这样的策略出现从因果关系的约束,自然是强加在反射和透射波包的考虑。

英文摘要:

When a monochromatic electromagnetic plane-wave arrives at the flat interface between its transparent host (i.e., the incidence medium) and an amplifying (or gainy) second medium, the incident beam splits into a reflected wave and a transmitted wave. In general, there is a sign ambiguity in connection with the k-vector of the transmitted beam, which requires at the outset that one decide whether the transmitted beam should grow or decay as it recedes from the interface. The question has been posed and addressed most prominently in the context of incidence at large angles from a dielectric medium of high refractive index onto a gain medium of lower refractive index. Here, the relevant sign of the transmitted k-vector determines whether the evanescent-like waves within the gain medium exponentially grow or decay away from the interface. We examine this and related problems in a more general setting, where the incident beam is taken to be a finite-duration wavepacket whose footprint in the interfacial plane has a finite width. Cases of reflection from and transmission through a gainy slab of finite-thickness as well as those associated with a semi-infinite gain medium will be considered. The broadness of the spatiotemporal spectrum of our incident wavepacket demands that we develop a general strategy for deciding the signs of all the k-vectors that enter the gain medium. Such a strategy emerges from a consideration of the causality constraint that is naturally imposed on both the reflected and transmitted wavepackets.

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