The Beam Propagation Characteristics Of Semiconductor Lasers

Because of their compactness, lightness, and low cost, semiconductor lasers are of importance for the delivery of high-power beams, providing highly efficient miniaturized light sources in many scientific and engineering applications.However, their potential applications are limited by the poor output-beam quality. Because of the shape and the waveguide properties of their active areas, semiconductor lasers generate large divergence-angle beams. The emitter size of a high-power single emitter is approximately several hundred micrometers; there semiconductor lasers operate generally in a multimode state. Therefore the far field distribution of a high-power semiconductor lasers array(SLA) is rather complicated, so appropriate models are very important for describing the beam of semiconductor lasers in almost all applications.The characteristics of irradiance distribution, propagation of several kinds of semiconductor lasers are studied in this paper. New models for describing the beam of semiconductor lasers are proposed, the configuration and principle of semiconductor lasers and their mode field distributions are presented. The intensity expression has been derived. The main work of this dissertation is summarized as follows:Based on the analysis of the beam output characteristics of one kind of semiconductor lasers, the generalized Collins integral were used, the transformation properties of there semiconductor lasers beam passing through optical system is studied. The analytical expressions of intensity distribution are derived and numerical examples are illustrated.Describe the far field distribution of one kind of semiconductor lasers by Hermite-cosine-Gaussian beams. The propagation characteristics of Hermite-cosine-Gaussian beams passing through an optical system with hard-edge aperture is studied, by means of expansion of the window's function of the hard-edge aperture into a finite sum of complex Gaussian functions, the approximate analytical propagation equations of laser beams are derived. It furnished in analyzing physically the propagation properties of beams of there semiconductor lasers.A novel model is proposed for describing the beam output characteristics of a kind of high-power semiconductor lasers. Double decent elliptical Gaussian beams solution to the wave equation is obtained, by the generalized Collins integral. The propagation characteristics of double decent elliptical Gaussian beam are studied. The propagation formula of passing through optical systems is derived, the analytical expressions of intensity distribution are derived and numerical examples are illustrated. Furthermore, the parameters, such as beam width and divergence angle, are also introduced to describe propagation properties. The theoretical results agree with experimental results well. It furnished in analyzing physically the propagation properties of the beams of high-power semiconductor lasers.A new model for describing the far field with a double peak structure of a high-power semiconductor lasers array is proposed. Sinuoids and square window function were taken to describe near field structure of laser diode array in parallel direction, the beam propagation properties are studied by use of the off-axis theory, the far-field solution of the Helmholtz equation can be obtained by use of the boundary condition at the output plane of the laser diode array. The computed results agree well with the measured far-field data of practical devices. This model has a simple mathematical structure, and is expected to provide a useful tool for the design of a beam shaping system and the analysis of the propagation properties of the high-power laser diode beams.Several methods to evaluate beam quality of semiconductor lasers are introduced, the strongpoint and shortcoming of them in evaluating beam quality of semiconductor lasers are also discussed.A new method for evaluating beam quality are presented, a parameter for evaluating beam quality of laser diode is given, which can be used to describe the difficulty of collimating the beam of semiconductor lasers.