Coherence condition

Imagine you have a bunch of toys scattered on the floor. Now, you want to arrange them in a certain way so they look nice and organized. In order to do this, you need to make sure that each toy is in its right place and it's not interfering with the other toys around it. This is what we call a "coherent" arrangement.

In physics, coherence is used to describe how waves (like light or sound) interact with each other. When waves are coherent, it means that they're all moving in the same direction and have the same frequency. This creates a nice organized pattern, just like the toys on the floor.

Now, let's say you have two sources emitting two different waves. If these waves are incoherent, it means that they are not aligned properly and are interfering with each other in a chaotic way. This creates a messy and disorganized pattern.

The coherence condition is a rule that tells us when two waves are coherent and when they're not. It's like a set of instructions that helps us arrange the toys on the floor in a coherent way. If we follow these instructions, we can create a nice and neat arrangement, just like when waves are coherent.

So, to sum up: coherence condition is a rule that tells us how waves should interact with each other in order to create a nice and organized pattern, just like when we arrange toys on the floor.