What knowledge does optics include?

Optics is the physical discipline that studies the behavior and properties of light (electromagnetic waves) and the interaction of light and matter. Traditionally, optics only studied visible light; modern optics has expanded to include the study of the full band of electromagnetic waves. Light is an electromagnetic wave, which in physics is described by a system of Maxwell's equations in electrodynamics; at the same time, light has wave-particle duality, which needs to be expressed in quantum mechanics.

To learn about lasers you can look at the classic textbook: Principles of Lasers - Bingkun Zhou;

If you are a beginner, you can start with geometrical optics: look at Applied Optics written by Yuk-Ying An of the North Polytechnic Institute