倏逝媒质中的波前传播
Front Propagation in Evanescent Media
摘要：
我们调查的时间演化的波在倏逝介质中产生的源在这种介质中，并观察到在一定距离以外的源的位置。其目的是找到一个描述因果过程的速度，因此，对于具有相对论色散的介质，它受到光速的限制。该波函数包括由源的开始产生的宽频率先导和携带源的振荡频率的单色波前。对于具有类薛定谔色散的介质，单色波阵面以与穿越时间一致的速度传播，而在相对论情况下，波阵面的速度受到光速的限制。对于一个尖锐的开始源，先行者没有衰减，并在幅度远远超过单色前。相比之下，对于频带有限的源，先导也会衰减并变得与单色前沿相当：与传播情况一样，存在一个时间，在该时间，单色波增强了宽频率先导。
英文摘要：
We investigate the time evolution of waves in evanescent media generated by a source within this medium and observed at some distance away from the location of the source. The aim is to find a velocity which describes a causal process and is thus, for a medium with relativistic dispersion, limited by the velocity of light. The wave function consists of a broad frequency forerunner generated by the onset of the source, and of a monochromatic front which carries the oscillation frequency of the source. For a medium with Schrödinger-like dispersion the monochromatic front propagates with a velocity which is in agreement with the traversal time, and in the relativistic case the velocity of the fronts is limited by the velocity of light. For sources with a sharp onset, the forerunners are not attenuated and in magnitude far exceed the monochromatic front. In contrast, for sources which are frequency-band limited, the forerunners are also attenuated and become comparable to the monochromatic front: like in the propagating case, there exists a time at which a broad frequency forerunner is augmented by a monochromatic wave.
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