Laser Physics

Abstract

These lecture notes present a comprehensive introduction to laser physics, covering the fundamental principles of light amplification, resonator theory, and ultrafast laser phenomena. The course begins with the historical development of lasers and a detailed analysis of the physical properties of laser radiation, including coherence, directionality, monochromaticity, and intensity. The theoretical foundation is established through Einstein coefficients, Planck’s radiation law, line broadening mechanisms, and key solutions of the wave equation such as Gaussian beams and Hermite–Gauss modes. The principles of optical amplification are developed using two-, three-, and four-level systems, emphasizing population inversion, pumping mechanisms, and mode competition. A phenomenological laser model is introduced to describe laser dynamics and threshold conditions. The treatment then advances to optical resonators, including planar and spherical cavities, stability criteria, and the ABCD matrix formalism for beam propagation. The final part of the course focuses on ultrashort laser pulses and light propagation in dispersive and nonlinear media. Topics include phase, group, and signal velocities; dispersion and absorption; Kramers–Kronig relations; and the dipole model of polarization. Nonlinear optical processes are examined in detail, including second- and third-order nonlinearities such as frequency doubling, optical rectification, Kerr effect, self-focusing, self-phase modulation, and four-wave mixing. Overall, the lectures provide a unified theoretical framework connecting quantum optics, wave propagation, and nonlinear phenomena, equipping students with both the conceptual understanding and analytical tools necessary for modern laser science and ultrafast optics.