Two kinds of basic problems in the interference of light

In the teaching of light interference, we talked about that the interference occurs when two beams of light have the same vibration direction, the same frequency and the same phase or constant phase difference. However, the temporal coherence dominated by the length of the wave train, and the spatial coherence dominated by the size of the light source are usually neglected. We will take Thomas Young's tow-slit interference as an example, introduce the temporal and spatial coherence, as well as the interference intensity dominated by the temporal and spatial coherence.