| For laser diode pumped all-solid-state blue laser sources, there are more advantages than traditional lasers, such as high efficiency, high stability, compactness and long lifetime. They are widely used in numerous fields such as optical communication, high-density optical data storage, color displays, high-resolution printing, and underwater communication which is a hotspot of field laser research in recent years. The more practical way to get an effective blue laser system can be realized by frequency doubling of 946 nm laser based on the transition 4F3/2â†'4I9/2 in Nd:YAG crystal. However, there are some difficulties in obtaining efficient laser operation at 946 nm using Nd:YAG, because the efficient 946-nm lasing is considerably harder to achieve than the 1064-nm lasing. The quasi-three-level nature of the 946-nm transition results in a serious re-absorption loss at room temperature. In addition, the stimulated emission cross-section of this transition is about one order of magnitude smaller than that of the 4F3/2â†'4I11/2 transition at 1064 nm. Although the blue laser has developed a lot, the level of development of the blue laser and the other band should not be mentioned in the same breath. The stability of output power of blue laser will be conducive to further extend to applications in R & D, industry and life. Based on the technical problems, we joined the designed ranks of the laser diode pumped all-solid-state blue laser.The main job of this thesis is giving a comprehensive analysis on the main elements such as pump source, laser crystal, the frequency-doubling crystal and the temperature control system which constitute our all-solid-state blue laser. The whole project such as cavity design, coating design, mode matching, beam quality were analyzed with a comprehensive analysis. The final goal is to be able to design and assemble an experimental system of blue laser with a high stability of the output power and keep the system in optimal condition through designing all the elements of the system. The main theory of our thesis is based on theory of quasi-three-level transition and nonlinear harmonic generation. The main content of this thesis will be introduced in the following four aspects:Firstly, the application of all-solid-state lasers was presented. The development prospects and research background of all-solid-state lasers was summarized comprehensively. At last the methords of obtaining the blue laser were introduced.Secondly, the efficient intracavity frequency doubling of 946-nm cw Nd:YAG laser end-pumped by a diode laser was more systematic and comprehensive theoretically studied. It mainly contains the quasi-three-level theory which the 946 nm infrared light was produced by Nd:YAG crytal. The expression of threshhold and interior and exterior slop efficiency were analized, also the theory of frequency-doubling was introduced, and the principle of phase matching and parameters which influence frequency-doubling efficiency were discussed. Attributes of three nonlinear crystals (BBO, LBO and BIBO) have been analyzed. The crystal parameters related to frequency-doubling efficiency were presented and compared. Here we emphasized on the BIBO crystal. It can provide a theoretical guidance of optimizing our laser.Tirdly, we had a detailed researchment on the structure of our experimental system and the principles of design. It mainly include: 1)the choices of pumping source and coupled sysem; 2)the design of cavity resonator; 3)according to the natural of mentioned frequency-doubling crystal,we chose suitale crystal for our experimental system; 4)design of suitable coatings for the quasi-three-level system; 4)the selection of pump source and its coupling system; 5)the design of temperature control system(We measured temperature of crystal by temperature sensor, controled the drive current of semiconductor cooling device, designed the symmetric heat sink. It will keep the laser crystal on our setting temperature and the temperature can be continuously adjustable. The constant temperature presicion is high. As a result, the population of lower-level can be decreased and the thermal stability of cavity can be enhanced. At the same time the reabsorption which will influence the threshold and power of fundamental frequency will be weaken effectively. Other temperature contorl systems can be designed on the basis of this set of systems.The last part is about measurement and analysis of the experimental result. It include the relationship of output power of LD and pump current, the condition of coatings, the spectral property of blue laser and the far-field spot of blue laser, the influence of the temperature of Nd:YAG crystal on the threshold pump power, the relationship between output power of blue laser and the length of cavity, the relationship between the output powers of the blue laser and different pump powers, stability of the ouput power of blue laser. We analyzed the reasons related to defect of the beam quality.According to the theoretical analysis and the investigation of all parts of experimental apparatus, we took the common Nd:YAG crystal and designed a simple and compact resonant cavity. The whole system was pumed with a diode laser. The maximal output power of blue laser was 78.1 mW as the pump power was 2.57 W. The corresponding optical conversion efficient was 3.04%. The output stability was better than 0.5%, which has a great improvement compared with the same type of laser. In our experimental system, the design of precise temperature control system and cavity resonator played an improtant role in the stability of output power. |
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