论电磁波传播中的负速度

On a Few Problems Related to the Negative Velocities of EM-waves Propagation

近10年来,多国科学家以实验研究了在短波、微波、光频和太赫波频段发生的超光速现象。在许多情况下,是发送脉冲后使之作负速度波传播,从而实现超光速传播的。本文概述了在负速度波传播方面的理论研究和实验研究。例如,实验中使光脉冲通过原子气室,其峰值到达入口前即在出口处浮现,呈现负渡越时间和负群速。故群速可以大于光速,可以为无限大,甚至可以为负。近年来,实验和观察中累累发现负速度的超光速现象,故可以认为它是科学研究的前沿之一。

In last decade, faster-than-light （superluminal） propagation of short waves, microwaves, light waves and THz waves has been studied experimentally in several countries. Many of the attempts to send pulses faster than the speed of light involved a phonomenon called negative-velocities wave propagation. In this paper, we give a bird-eye view of the theoretical and experimental iesearch work on negative-velocities wave propagation. For example and experimentally, a light pulse propagating through the atomic vapor cell has its peak reaching the exit side before entering it, resulting in a negative transit time, and negative group velocity. So that the group velocity vs can be greater than the velocity of light c, can be infinite and even negative. In recent years, many superluminal phenomena of negative-velocities have been discovered in experiments and observations, so we say it is a new frontier in sciences research.