Study On The Characterizations And Applications Of High Power Semiconductor Lasers

Several key issues of semiconductor lasers are discussed in this paper. Study on the characterizations of irradiance distribution is significant for the practical applications of laser beam shaping and solid-state laser pumping. The characterizations of irradiance distribution, the far-field error and the near-field distributions of semiconductor lasers, the discussion of evaluation on beam quality of semiconductor lasers, a new beam shaping device, and the tightly coupled pumping technology are discussed in this paper. The key issues discussed in this paper are divided into four parts:In the first part of this paper, the far-field error and the near-field distributions of semiconductor lasers are studied synthetically. "Relative error volume" gave the maximum error range of the far-field error. For practical work, it is important to provide an accurate description of the far-field error in terms of the source error. The "critical point" of the far-field phase error is derived, analyzed and proposed to decide the off-center source error. Numerical results show that the off-center distance should be used in describing the source error and analyzing the far-field errors, and the "critical point" is the useful parameter in analyzing the source error for the inverse problem.Based on the far-field data, a new approaching trust region local optimization algorithm has been used to determine the near-field distribution. Numerical results demonstrate that the field distribution function of the source could be approached by a sum of some simple functions, and our method is simple and of high efficiency.In the second part of this paper, the characterizations of irradiance distribution are studied, and the discussion of evaluation on beam quality of semiconductor lasers is mainly researched. The intensity expression of laser diode bar and laser diode stacked array have been derived and illustrated with numerical examples. The intensity changed obviously with distances. Based on the beam characteristics of semiconductor lasers, a new parameter for evaluating beam quality of high power semiconductor lasers is introduced. The shortcomings of M2 factor used in evaluating beam quality of semiconductor lasers are discussed and its limitations are pointed out. Moreover, some important aspects of the beam quality factor are discussed. The main factors to influence collimating the beam of semiconductor lasers are analyzed. Our results give us grounds to make the following conclusions:the smaller the value of the new parameter is, the more easily the beam is collimated. In the third part of this paper, a new beam shaping device of diode laser stack is presented. The shaping element consists of a glass pyramid with spherical or plane output surface. The large divergence angle and the overall aperture area are compressed by this beam shaping system. The transformation characteristics are presented and the optimization performance is investigated based on the ray-tracing method. Analysis shows that high irradiance can be obtained. This beam shaping system can be easily fabricated and has large alignment tolerance.In the fourth part of this paper, tightly coupled pumping technology of micro-modularization DPL is studied. An experimental equipment of laser diode symmetrically side-pumped Nd:YAG slab laser is designed. The influence of laser diode on pump distribution of gain medium is measured and analyzed. Study shows that more diodes lead to better pumping intensity distribution; the least absorption coefficient of laser medium, the best pumping intensity distribution; the smaller distance between diode and laser medium, the worse pumping intensity distribution. The efficiency of coupling,>90%, accords with the design index.