| A diode-end-pumped solid-state laser with high efficiency, high output power, a goodspatial beam profile, and good stability is highly desired for use in material processingand other scientific applications such as pumping other laser crystals. The Nd:YVO4crystal was identified as a promising gain medium of the diode-end-pumped solid-statelaser because of its many advantages such a high absorption over a widepump-wavelength bandwidth ,a large efficient stimulated emission cross-section.However the capability of heat exchange is bad, so the influence of thermal effect isobvious. So the development of the Nd:YVO4 crystal is limited in the high power field.Now it has been played an important role in the development of Nd:YVO4 crystal thathow to eliminate the influence of thermal effect. Cr4+:YAG crystal was invented in 1988.It is a new type laser crystal in near infrared ray. Cr4+:YAG crystal has good capabilityof heat exchange, steady physical and chemical characters. It can generate passiveQ-switching,passive mode-locking,self mode-locking by continuous or pulsed pumped.Cr4+:YAG crystal is attractive in light communications,medical applications,lasertechnology field. The dissertation presents results of theoretical and experimentalresearches on the performance of thermal effect of Nd:YVO4 crystal and passiveQ-switched and mode-locked Nd:YVO4 / Cr4+:YAG solid-state laser. The contents canbe outlined following as: (1) summarization (2) the theoretical and experimental thermaleffect researches of the diode-end-pumped Nd:YVO4 (3) the theoretical andexperimental researches of passive Q-switched and mode-locked Nd:YVO4 /andCr4+:YAG solid-state lasers.(1) The history and progress of diode-pumped solid-state lasers are reviewed;andthe characters of the diode-end-pumped solid-state laser are presented;then thedissertation presents the crystals of fitting diode-end-pumped, and summarizes theresearches of thermal effect of the diode-end-pumped solid-state laser .Then reviewingthe ways of mode-locking operations.(2) Introducing the characters of the Nd:YVO4 crystal. Based on the rate equations,we show the output formula by continuous wave pumped .Then using the formula tocalculate the conditions that can get the best output .By the experiments, we comparewith different cavity lengths, transmissivities of output mirror and duty cycles. Theresults prove that the theoretical counts are exactly. Then by qualitative analysis andquantitative calculation, we give the explanations about the experiments.(3) Introducing the characters of Cr4+:YAG crystal. And then we review thefluctuation mode, the second threshold value and the self focusing in the passivemode-locked process. The energy level and the main transition of the Cr4+:YAG crystalare discussed and analyzed .And by basic rate equations, the dynamic process ofsaturable absorption is described. And then we analyze the conditions that the Cr4+:YAGoperates on Q-switching or mode-locking .Then the saturation intensity of the secondexcited state is calculated. By the ABCD matrix, we calculate that the stable area ofresonance cavity in different pumped powers, and the changes of the facular radius withdifferent cavity lengths and pumped powers. And also we calculate the stable area ofresonance cavity in different duty cycles with 8.5W pumped power. The experimentpictures are shown about different cavity lengths and duty cycles. Then we explain theexperiment results, especial the freakish pictures. And then we advance an explanation,and show the theoretical pictures .It found that the theoretical pictures are accord withthe experimental pictures. So it indicates that the explanation is reasonable. |
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