I am seeking references to the first articles regarding the observation of polaritons.
Found something today.
"Actually the concept of polaritons has been described in words as early as 1946 [F. Bloch, Phys. Rev., 70, 460 (1946)] in nuclear paramagnetic resonance, however without using the then still unkown term 'polariton'."
Klingshirn, Claus F., Jul o6 2012, Semiconductor Optics Springer Berlin Heidelberg, Dordrecht, ISBN: 9783642283628