I don't have the time now to study QFT in depth but I need some basic knowledge about QED and quantum forces (like casimir). I want to study the role of casimir force to solid state devices (photonic and plasmonic devices). Which part of QFT is needed to study for now and which books are going to help me for this purpose? I am an undergraduate (advanced courses taken: quantum mechanics, electrodynamics, statistical mechanics and solid state physics). I work on plasmonics and photonic crystals.