自鎖模雷射的研究與應用

Abstract

本文主要是藉由Nd:YVO4和Nd:GdVO4較高的第三階非線性特性，搭配簡易的直線型雷射共振腔，且無須外加額外的元件，成功實現高重複率(GHz)自鎖模雷射。在2.5W激發功率下，可以產生0.8W的輸出,其波長為1064nm，脈衝寬度7.8ps；除了1064nm波段之外，在10.2W激發功率，亦產生了1342nm的1.2W雷射輸出，其脈衝寬度為12ps。接著利用空間燒孔效應(spatial hole burning effect)來控制雷射輸出的縱模數，藉由縱模數目的控制來穩定自鎖模雷射，除了實驗結果外，這裡也建構了理論架構，且與實驗結果吻合。透過這個穩定的自鎖模雷射，本文也提出ㄧ個量測可穿透式晶體的折射率及熱光係數(thermal optical coefficient)的方法，其主要方法是利用自鎖模雷射重複率的改變來推算出。接著我們利用離軸激發方式，產生具有高階橫向Hermite-Gaussian (HG)模態的自鎖模雷射，並且藉由ㄧ對柱面鏡，在腔外將其轉換成帶有軌道角動量的高階Laguerre-Gaussian模態，透過這樣的腔外轉換，可以產生皮秒的光束漩渦。除此之外，我們在也利用當有兩個高階模態偶合時，其自鎖模雷射所產生的拍頻現象來量測晶體的熱透鏡焦距。

The large third-order nonlinearities of Nd:YVO4 and Nd:GdVO4 are employed to realize the compact efficient self-mode-locking in the range of several GHz in solid-state lasers with a simple linear cavity. With a pump power of 2.5 W, the lasers produce greater than 0.7 W with the pulse width in the picosecond region at the operating wavelength of 1064 nm. Furthermore, we also have demonstrated the self-mode-locked Nd:YVO4 laser at 1342 nm. The average output power was up to 1.2 W at an incident pump power of 10.2 W. The pulse width was experimentally found to be less than 12ps. In order to improve the stability of self-mode-locked lasers, we have demonstrate the control of Nd:YVO4 laser. The experimental results reveal that reducing the number of longitudinal lasing modes can diminish the fluctuation to effectively improve the pulse stability. Considering the spatial hole burning (SHB) effect, an analytical expression is derived to accurately estimate the maximum number of longitudinal lasing for a practical design guideline. Therefore, the stable self-mode-locked laser can induce a novel method to measure the refractive indexes and thermal optical coefficient of certain crystals. The experimental results are in good agreement with the results in texts. Besides the fundamental mode self-mode-locked lasers, we have reported the self-mode- locked Hermite-Gaussian Nd:YVO4 lasers with an off-axis pumping scheme. With a pump power of 2.2 W, the average output power for 3.5 GHz mode-locked HG modes vary in the range of 350-780 mW for the TEM0,m modes from to . We also use simple astigmatic mode converters (AMC) to convert the mode-locked HG TEM0,m beams in to Laguerre-Gaussian (LG) modes for generating picosecond optical vortex pulses. Furthermore, the modulated pulse trains are observed as there are two adjacent transverse modes coupling. The modulated frequencies can apply to determination of thermal lens in mode-locked lasers.