渐逝波（evanescent wave），又称为消逝波或，倏逝波，是指当光波从光密介质入射到光疏介质时，发生全反射而在两种不同介质的分界面所产生的一种电磁波。由于其振幅随与分界面垂直的深度的增大而呈指数形式衰减，而随切线方向改变相位，因此也是一种表面波。。渐逝波是近场的，强度随着呈指数衰减的，没有被吸收的，其解是距边界的距离x的函数。渐逝波作为波动方程的解，可以运用于任何波动方程。形成于两种拥有不同的波动性质的介质的边界上。在距离表面三分之一波长的距离下最为强烈。特别的，渐逝波可以发生在除了光学的其它情况下，如电磁辐射、声学、机械波的情况下。

In electromagnetics, an evanescent field, or evanescent wave, is an oscillating electric and/or magnetic field which does not propagate as an electromagnetic wave but whose energy is spatially concentrated in the vicinity of the source (oscillating charges and currents). Even when there in fact is an electromagnetic wave produced (e.g. by a transmitting antenna) one can still identify as an evanescent field the component of the electric or magnetic field that cannot be attributed to the propagating wave observed at a distance of many wavelengths (such as the far field of a transmitting antenna).