Photon Interaction - 1

[Music] okay welcome to introduction to photonics we are we've been talking about the particle nature of light in the past few lectures so we introduced water photon s and what are the properties of photons and then towards the end of last week we had talked about interaction of light with matter so we

started talking about absorption of light and we looked at the specific example of light getting absorbed in rhodamine 6g and that sort of absorption process essentially required us to tune into the photon picture and say that if the photon energy corresponds to the energy difference in in this particular material then it's it's likely to get

absorbed so we will continue to build on that picture so what we will do for the next few weeks is to identify the fundamental principles of photon interaction with atoms we just started doing that we will go into that a little more detail and the specific motivation for considering that is we want to

understand light generation and amplification okay because so far we've been looking at ray optics wave optics electromagnetic optics photonics and in all of this we just figured there is some source out there which is giving us all this light now that source how does that work right so what what goes into explaining

light generation and amplification and in in certain ways once we understand this then we'll be in a better position to understand why certain sources are not so temporally coherent wise other sources are temporally coherent why certain sources are spatially coherent or not you know although all those things you know we will be able to

explain once we understand this okay to understand this let's just consider an atom once again just like we did in one of the previous lectures we have an atom with energy levels let's say e 1 and E 2 e 2 being greater than e 1 and let us see what all are possible between a 1