What is the first paper to report observations of polaritons?

I am seeking references to the first articles regarding the observation of polaritons.

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Related question by OP: physics.stackexchange.com/q/49749/2451 –  Qmechanic Jan 10 '13 at 15:34
@Qmechanic Yeah, I was asked to change the question and limit its scope. This question is similar, but fundamentally different, and hopefully more appropriate for the stackexchange venue. –  tlengman Jan 10 '13 at 17:10
Just to let you know the system, when you are asked to change the question (usually by a moderator, in this case @DavidZaslavsky), you are supposed to edit the original question, you are not supposed to create a new duplicate-like post. –  Qmechanic Jan 10 '13 at 19:27
@Qmechanic Oh, okay, thank you. –  tlengman Jan 10 '13 at 19:38
@DavidZaslavsky I made this question in order to improve upon my first question, but Qmechanic let me know that I should have just altered the old question. What should I do now that I have made the new one? Should I delete this one or the first one, or just leave them both. They really are very different, they would require completely different answers etc. –  tlengman Jan 10 '13 at 19:40