ABSTRACT
Laser beam divergence was considered using the components of the Poynting vector. A physical interpretation of the real and imaginary parts of the "longitudinal" field component (along the z axis, the direction of beam propagation) is given in an exponential representation. The longitudinal field component was shown to be the reason for the formation of laser beam divergence. This fact was used to reveal fundamental differences between Laguerre-Gaussian beams and incoherent rays in the focal region. The possibility of using selective action on the longitudinal field component to decrease the divergence of Laguerre-Gaussian beams is discussed.
ABSTRACT
We developed an iteration algorithm for open resonator simulation and employed it in studying the dynamics of mode formation. Simulations of an axially symmetrical empty resonator rely on an analytical description of radiation diffraction from a narrow ring. Reflection of an incident wave with a specified amplitude-phase distribution from the mirror is calculated by the Green function method. The process of mode formation is characterized by relaxation oscillations of various frequencies depending on the resonator parameters. The evolution of the relaxation oscillation amplitude can be aperiodic in nature, or it can occur as beats of a different frequency. It has been shown that there is a consistency between the known conditions of paraxial resonance obtained in the approximation of geometric optics and the aperiodic processes of evolution of relaxation oscillation amplitude in mode forming. An investigation has been performed on the factors affecting the time of mode formation. The possibility has been shown for multipass mode suppression and TEM(10) mode generation by the use of an absorber mask on the resonator mirror.
