A historical introduction. Loudon sets the stage by showing the failure of classical electromagnetism and the birth of the photon concept. He derives Planck’s blackbody radiation formula from first principles, establishing the statistical nature of light.
The mathematical core. Here, Loudon introduces annihilation and creation operators (a and a†). If you have never understood why ( [a, a†] = 1 ), this chapter will change your life. He covers number states, coherent states (discovered by Schrödinger), and squeezed states. loudon quantum theory of light pdf
The crown jewel of the book. Loudon introduces the optical equivalence theorem and the P-representation. He distinguishes between fully coherent light (lasers), partially coherent light (thermal lamps), and squeezed light. A historical introduction