The spectral content of a plane wave train refers to the range of frequencies present in the wave, which can be either temporal or spatial. A plane wave propagates in one direction while being infinite in the other two, allowing it to encompass various frequencies. If the wave is polychromatic, it will exhibit a temporal frequency spread due to its finite duration. Alternatively, a wave train with finite spatial extent will display a spread in spatial frequencies. Understanding these aspects is crucial for analyzing the characteristics of wave trains in different contexts.
