介质中光脉冲的超光速问题分析

Analysis on the Issue about Superluminal Velocity of Light Pulse in Medium

光具有相速度、群速度和波前速度,辨明三者与真空光速c之间的关系是十分必要的.光在折射率小于1的介质中传播时,相速度能够超光速;光脉冲在具有反常色散的介质中传播时,群速度能够超光速.在任何情况下,光脉冲的波前速度和信息传播速度都无法超光速.通过在课程中引入光前驱波现象,说明光脉冲的波前速度无法超过真空光速c.

Light has phase velocity,group velocity,and wavefront velocity.It is necessary to identify the relationships between these three velocities of light in a dispersive medium and the velocity of light in vacuum.In a medium with a refractive index of less than 1,the phase velocity can exceed the light speed in vacuum.When propagating in a medium with anomalous dispersion,the group velocity of a light pulse can exceed the light speed in vacuum.However,the wavefront speed and information propagation velocity of a light pulse cannot exceed the light speed in vacuum.By introducing the phenomenon of optical precursors into the physics courses,we can clearly show that the wavefront velocity of light pulses cannot exceed the light speed in vacuum.