Theoretical And Experimental Research On Laser Diode Pumped All Solid State Blue Lasers

Laser diode(LD) pumped all solid state blue lasers have more advantages than traditional gas blue lasers, such as high efficiency, compactness, high stability, and long lifetime. They are widely used in many fields such as medicinal diagnose, precise machining, spectroscopic analysis, optical printing, high density data storage, isotope separation, scientific research and laser entertainment in general, and it is a hotspot of all-solid-state laser research in recent years. In this dissertation, the theoretical and experimental research on LD pumped all solid state blue laser can be outlined as:1. The development process of all-solid-state lasers was presented firstly, as well as its main characters and application field. The researching background of LD pumped all-solid-state blue lasers were introduced along with methods to achieve blue laser, and research evolution of blue laser were summarized over domestically and abroad.2. According to theory of qausi-three-level lasers, considering re-absorption lose of laser medium, laser threshold and slope efficiency was investigated for several circumstances, as well as optimal crystal length. The results show that an optimal laser crystal length can lead a minimum threshold for the system at low pump power, and larger crystal means higher external slope efficiency at higher pump power. Gaussian pump energy makes for low threshold for side pump configuration, while top-hat pump energy is propitious to high out put power. Physical and optical properties of several laser crystals used in blue lasers were compared.3. Considering the process of quasi-homochromatic three light wave coupling under adiabatic utmost, second harmonic conversion efficiency were present under little and large signal approximation. Non-linear optical phase matching efficiency was discussed here. Property of several nonlinear optical crystals of blue lasers were compared.4. A graphic analyze method were used to analyze the working property of V and Z type folded laser resonator under the effect of thermal lens of laser medium. The stable range of these resonators was influenced mainly by the length of its first arm, a wider thermal stable range means smaller optical module. The V type folded resonator's astigmatic can be compensated partly by insert a suitable Brewster plate in the cavity.5. Temperature field and thermal lens effects of laser diode end pumped composite YAG rod were investigated and compared with conventional Nd:YAG through a numerical analysis method. The results shown that the highest temperature of these laser medium discrepant increasing as absorption coefficient increase under the same pumping condition, and the value of f(GRIN) close to each other approximately, this means little thermal length effect in composite laser rod. Phase detention of thermal effect cannot be equivalent to a spherical lens, and thus an optimization module ratio (W_o/w_p) of pump and laser mode should be choice in a laser system. Interference pattern of thermal effect of laser crystal were detect experimentally.6. Experimental research: Firstly, reflectivity of laser cavity mirror was measured by Cavity-Ring-Down method. Following that, we utilizing 3W LD laser end pumped Nd:YAG crystal, and type I phase matching BIBO nonlinear crystal were select for intra-cavity frequency doubling blue laser, 220mW blue laser at 473nm were obtained, corresponds to an optical-optical conversion efficiency of 7.3%. And the stability of blue laser excelled 3%. A new type of high efficiency blue laser product with good beam quality and high stability was exploited based on our research results.Secondly, in another experiment, fiber coupled high power diode laser were select to end pump Nd:YAG crystal, 3.2W infrared laser at 946nm were obtained. BIBO were selected for intra-cavity frequency doubling, 710mW blue laser at 473nm were obtained. This laser system is in process of optimizing and production engineering realize.Laser spectrum around 900nm of Nd:GdVO₄ crystal were measured in cavity. The result shown that quasi-three level laser were depleting directly by four level lasers transition. Transitions around 900nm of Nd:GdVO₄ show a blue shift at increasing cavity losses.