This course should be taken by everyone in Optoelectronics Science and Technology, as it includes the basic principles of lasers, mechanisms and applications. After the completion of this course, students should know the following items: (1) The basic knowledge, characteristics, and the components of lasers, (2) The ray and wave propagation theory for cavities (3) Line broadening mechanisms, the analysis method of the rate equation, and the characteristics of gain coefficient for various kinds of materials, (4) The oscillation characteristics of a laser, the relaxation oscillation frequency and linewidth of lasers etc.