Basic concepts of electromagnetic theory; Coulomb gauge; intensity of electromagnetic field. Electrons in an electromagnetic field: from the Lagrangian to the Hamiltonian; canonical momentum. Interaction Hamiltonian. Semiclassical approximation; weak-field limit. Electric dipole approximation. Calculation of the optical susceptibility by using the density matrix approach. From optical susceptibility to absorption coefficient. Momentum of an electron in a periodic crystal.

We start carrying out the programme of covariant quantisation, focussing on the photon and tachyon state of the open string. The photon is used to explain the relation between the world-sheet and space-time perspective by matching properties of the photon state to those of the Maxwell field. The tachyon gives us the opportunity to talk abouttachyon condensation, string field theory, and the search for the true ground state of string theory.

Chapter 1: introduces the subject – starting by endeavouring to define what the term ’photonics’ might mean and following this with a very brief exploration of the basic concepts.There is then a brief discussion about applications which impact upon our everyday lives.An outline of the book and the reasons for its being presented in this particular format follows.Finally, there is a very brief mention of the background in other complementary disciplines which complement photonics.