Hello, yesterday when I posted, I wasn't thinking, there is a very obvious example of your wave diagram. An inexpensive laser demonstrates granular dots of light that move about in patterns that you describe. This would be an amplified picture of coherent movement within the medium as light is reflected back and forth within. Do you have an Email address? I will send the diagrams that I mentioned yesterday, it would be quicker as I am not yet ready to go into a knol on that subject yet.