利用鍵合Nd:YVO4/Nd:GdVO4晶體產生雙波長被動鎖模雷射之研究

Abstract

本論文主題是利用鍵合晶體Nd:YVO4/Nd:GdVO4在線性共振腔的架構下，探討被動式(SESAM-based)鎖模雷射分別在利用平行鍵合與切角鍵合這兩種不同鍵合方式的晶體下產生雙波長雷射時之表現有何差異。鎖模雷射在最近這幾年蓬勃的發展，且均能產生相當高的功率輸出。在被動鎖模雷射的系統中，如何有效的提升鎖模的品質是一門值得研究的課題。本論文設計兩種不同鍵結方式的晶體來達成雙波長之被動鎖模雷射之輸出。首先，我們理論地分析共振腔的穩定條件，得出共振腔長度與雷射模態的光束半徑的相對應性，以確保鎖模品質的高穩定性。然後根據此穩定條件所得之相對應的腔長比例，進一步利用兩種不同鍵合方式的晶體來產生雙波長雷射。相較於單波長的被動鎖模雷射的輸出已有相當具體且理論的實證，因此利用鍵合晶體產生雙波長的被動鎖模雷射有其研究的必要性。同時，不同的晶體鍵合方式對於所產生的雙波長雷射的品質及表現，也是我們相當有興趣的主題。經由我們的實驗設計，具體實現了雙波長被動式鎖模雷射，並在本論文中得出其不同的鍵合方式對於所產生的雙波長雷射將有著顯著的影響。最後我們探討利用三個元件組成的線性共振腔所進行的諧振自鎖模雙波長雷射的現象。

We develop the passively mode-locked (PML) operation in diffusion-bonded gain media by parallel-bonded and wedged-bonded structures. Both approaches are utilized in a simple linear cavity. Firstly, we experimentally found that , with SESAM-based, the parallel-bonded Nd:YVO4 and Nd:GdVO4 lasers can operate at the stable CW mode-locked state with the repetition rates of 300 MHz. The temporal trace shows multi-pulse mode-locked pulse trains with the cavity round-trip time of 3.36 ns, and it exhibits 7 mode-locked pulses in the single group with delay time of 160 ps. At an incident pump power of 12.7 W, the maximum output power of 2.6 W is obtained. The main peak width in the mode-locked pulses can be evaluated as 16.3 ps with assuming the Gaussian-shaped profile. The full modulation in every peak indicates the dual-central-wavelength mode-locked pulses to be well synchronous. In order to avoid the multi-pulse temporal structures, we use the wedged-bonded crystal to replace the parallel-bonded crystal. Then, we theoretically and experimentally confirm that we can flexibly control the power ratio of dual-center-wavelengths of 1064- and 1063-nm radiations with wedged-bonded Nd:YVO4 and Nd:GdVO4 gain media. Under the balanced dual-wavelength intensities, the maximum total output power of 2.5 W can be obtained at a pump power of 11 W. In the synchronous dual-wavelength mode-locked operation, the pulse repetition rate and the pulse duration are found to be 297.9 MHz and 24.7 ps. Moreover, the perfect temporal overlapping between the two-wavelength pulses incur a full modulation of optical beating with 1.8 ps pulse duration and 0.318 THz repetition rate. Finally, we have employed a linear three-mirror cavity to achieve the simultaneous harmonically self-mode-locking (SML) laser by the wedged-bonded Nd:YVO4/Nd:GdVO4 at 1063 and 1064 nm. In the long linear cavity setup, we utilized the method of couple-cavity to achieve the sixteenth harmonically self-mode-locking.