What's the mode of vibration between two reflections inside the retroreflector?

Can anybody Please tell me if a Circularly Polarised light (suppose left ) falls on a retroreflector, after suffering a total internal reflection it comes out to be a right circularly polarised light.But what is the mode of vibration in between the two reflections inside the retroreflector?

I am afraid I dont get your question.
So, you have a reflected light, why should the resonance happen?