利用超短雷射脈衝產生的高階諧波是一種極紫外光源與軟X光源其擁有著獨特的超短脈衝和高時空同調性的特徵[6]。這樣的光源讓我們有機會利用新的超快光源來探測原子分子與材料。到目前為止，大部分的應用都是使用較長的諧波波長，因為在較短波長的能量轉換效率極速下降。在雷射聚焦位置，相位不匹配將導致在不同位置產生的諧波形成破壞性干涉。 最近準相位匹配提供了可能的選擇是傳統相位匹配無法做的。參考[7]說明了利用對撞雷射脈衝，全光學式的準相位匹配是可被執行的有彈性與實際實驗方法[1][8]。 這裡我們報告關於增益高階諧波產生的研究。 第一章說明高階諧波的原理和一些相位不匹配的現象限制了雷射光轉換高階諧波效率。 第二章介紹準相位匹配技術的發展。 第三章描述實驗中所使用的多功能二十兆瓦雷射系統。 第四章提供一個可能比其它實驗還要多增益的轉換效率的方法。 我們將說明這個實驗的設計、架設、診斷系統與實驗進行的邏輯安排。 最後我們將說明初步的實驗結果與討論。 i High-order harmonic generation (HHG) driven by ultrashort laser pulses is a source of extreme-ultraviolet and soft X-ray light with the unique properties of ultrashort pulse duration and high spatial and temporal coherence [6]. This source has made possible new ultrafast spectroscopic probes of atoms, molecules and materials. So far, however, most applications have used relatively long wavelengths, because the conversion efficiency rapidly decreases at shorter wavelengths. Phase mismatches can cause severe destructive interference for high-order harmonics light emerging from different locations in the laser focus. In recently, Quasi-phase matching (QPM) provides a potential alternative when conventional phase match is not possible. Ref [7] demonstrated that by using a counterpropagating laser field, all-optical QPM can be implemented in a manner that is both flexible and experimentally practical [1,8]. Here we reports on the research for enhancing high-order harmonic generation. Chapter 1 shows principles of high harmonic generation and several phase mismatch phenomena which limits the efficiency of converting the fundamental light into high-order harmonics. Chapter 2 introduces the development of QPM. Chapter 3 describes the versatile 20-TW laser system used in the experiments. Chapter 4 shows a method could enhance more conversion efficiency than others. We will illustrate the experimental design and setup, diagnostics, logical arrangement for experimental process. Final, we show preliminary experiment result and discussion.
