本論文研究之主要目的是探討單模Nd:YVO4/Cr4+:YAG雷射之運作，尤其是連續波及脈衝式兩種運作模式之間變遷時的變化。理論部分，我們考慮雷射腔內的駐波效應，對斜率效率做合理的解釋。實驗部分，一開始我們使用二極體雷射作為我們的幫浦光源，以Nd:YVO4雷射晶體做為端面鏡，再利用KTP晶體與薄膜偏振片建造一個折疊腔雷射。我們發現即使腔長達18公分，仍可以輕易的實現穩定單模運作 。當此雷射在幫浦光功率為570mw時，輸出功率為94mw，偏振比約200:1。在斜率效率與起振功率的測量實驗中，我們發現實驗值與理論值相當吻合，驗證了我們的理論推導。在折疊腔腔長8公分中，我們使用Cr4+:YAG晶體作為可飽和吸收晶體，KTP晶體作為選模裝置。藉由幫浦功率的改變，測量連續波及脈衝模式及兩者之間變遷時的光譜。我們發現雷射運作模式變遷的過程中，雷射光的波長沒有變化，輸出功率仍與激發功率保持線性關係。因而推斷這種脈衝形成的機制是雷射光的強度與可飽和吸收體的透明度兩者一消一長互相調製而成。 The main purpose of the thesis study is to investigate the single mode operation of a Nd:YVO4/Cr4+:YAG laser; especially the changes which occur during the transition between continuous wave (cw) and pulsed modes of operation. Theoretically, the standing wave effect in laser cavity is considered in evaluating the overlap efficiency so that a quantitative explanation to the slope efficiency can be made. In the experimental part, we used diode laser as our pump light source. A folded laser cavity was formed with a Nd:YVO4 laser crystal (serving as a terminal mirror), a thin-film polarizer, a KTP crystal and a output coupler. The KTP crystal and the polarizer function as a mode-selector. We found that stable single-mode operation can be easily achieved even when the cavity length is 18-cm long. At a pump power of 570 mw, an output power of 94 mw was obtained, and the vertical to horizontal polarization ratio is about 200:1. As far as the threshold pump power and slope efficiency of the laser are concerned, our experiments show very good agreement with theory. As the length of the folded cavity was changed to 8 centimeters, a Cr4+:YAG crystal was used as a saturable absorber. By changing the pump power, we measured the spectrum of the laser output which underwent a transition from cw to pulsed operation modes. We found that in the course of the transition, the laser does not change in its wavelength, and its output power still keeps the same linear relationship with the pump power. Thus, the mechanism of the transition may be simply attributed to the cross modulation between the intra-cavity laser intensity and the concentration of the absorbing centers within the Cr4+:YAG crystal.
