This book is a concise and comprehensive presentation of numerous fundamental concepts related to the light nature and its interaction with matter. The Dirac approach is used in the description of optics, population inversion, laser gain, and polarization. The book provides insight into practical laser and quantum mechanics. It also explains the use of quantum mathematics which is required to understand the photon as it is used in real systems. Practical, real-world, worked-out examples are used throughout as well as interferometric calculations using MATLAB®.