雷射驅動充氣毛細管波導之高階諧波產生;Laser-Driven High-Order Harmonic Generation from Gas-Filled Capillary Waveguide

NCU Institutional Repository > 理學院 > 物理研究所 > 博碩士論文 > Item 987654321/99312

請使用永久網址來引用或連結此文件: https://ir.lib.ncu.edu.tw/handle/987654321/99312

題名:	雷射驅動充氣毛細管波導之高階諧波產生;Laser-Driven High-Order Harmonic Generation from Gas-Filled Capillary Waveguide
作者:	林建和;Lin, Jian-He
貢獻者:	物理學系
關鍵詞:	高階諧波產生;毛細管波導;相位匹配;High-Harmonic Generation;Gas-filled Capillary Waveguide;Phase Matching
日期:	2026-01-27
上傳時間:	2026-03-06 18:36:17 (UTC+8)
出版者:	國立中央大學
摘要:	高階諧波產生（High-order harmonic generation, HHG）是近二十年在超快科學中快速發展的重要技術，可產生極紫外至軟X光波段的相干光源，並廣泛應用於阿秒脈衝產生、分子動力學量測以及材料中的超快電子行為研究。過去HHG主要在稀薄氣體中進行，過程可由三步驟模型描述，其截止能量受限於原子游離能與驅動雷射強度，因此如何提高轉換效率及推進更短波長，一直是努力的方向。從研究趨勢來看，現今HHG主要朝兩個方向發展：（1）產生更短的阿秒脈衝，典型方法是使用單週期或近單週期的驅動雷射，使HHG 只在單一半週期內發生，以獲得孤立阿秒脈衝。此類脈衝品質高，但目前驅動雷射能量受限制。（2）推進更短波段（更高能量）的HHG，利用較長波長的驅動雷射可將截止能量延伸，但由於游離率極低，諧波轉換效率普遍非常低，實驗也更具挑戰。本研究希望突破低游離率的限制，探討是否能從離子（如1+、2+）產生HHG，而非只依賴中性原子。若能有效使用高游離率環境（甚至達到一半以上的游離率），驅動雷射能量即可進一步提高，使可達到的截止波長顯著縮短。如此一來，可望突破傳統HHG的能量限制並大幅擴展極短波長的應用可能。然而，高游離率環境下的關鍵挑戰是有效的相位匹配。本研究採用毛細管波導來限制雷射發散並延長雷射與氣體的作用距離，並結合自製的中間診斷系統，包括焦點品質量測與頻域干涉儀量測電漿密度，使能夠直接觀察波導中的模態演化與相位匹配狀況，提供少見的詳細中間物理資訊。本研究分別使用不同內徑的毛細管（100、150、200 µm）於氬氣與氦氣中測試HHG產生。結果顯示：150µm毛細管在短脈衝（40fs）驅動下，於第27階諧波達到高於過去實驗的轉換效率；200µm毛細管在氬氣中成功產生超越傳統原子截止能量的諧波，而氦氣則成功將波段推進至8nm。本研究的成果說明，適當的波導條件、短脈衝、以及高游離率環境確實有機會突破傳統HHG限制，並支持HHG可能由高電離態貢獻的可能性。;High-order harmonic generation (HHG) is an important nonlinear process that can produce coherent radiation in the extreme ultraviolet and soft X-ray regions. It has been widely used in attosecond science and ultrafast dynamics studies. Traditionally, HHG is generated in gases and can be de scribed by the three-step model. However, the cut-off energy and conversion efficiency are limited by the ionization potential and phase-matching conditions. In recent years, HHG research has mainly followed two directions. One direction focuses on generating isolated attosecond pulses by using single-cycle or few-cycle driving laser pulses. This method can produce high-quality ultrashort pulses, but the pulse energy is low and it is difficult to reach very short wavelengths. The other direction aims to extend the harmonic cut-off by using longer-wavelength driving lasers. Although this method can generate higher photon energies, the ionization rate and conversion efficiency are usually very low. In this work, we explore another approach to HHG by studying harmonic generation from highly ionized media instead of only neutral atoms. By increasing the ionization level of the gas, higher driving laser energy can be applied, which may allow the harmonic cut-off to extend to shorter wavelengths. A major challenge of this approach is achieving phase matching under high plasma density conditions. To address this problem, gas-filled capillary waveguides are used to confine the laser beam and increase the interaction length between the laser and the gas. Capillaries with different inner diameters (100, 150, and 200 µm) are tested under various gas pressures and laser conditions. In addition, intermediate diagnostic systems, including focal spot measurements and frequency-domain interferometry, are used to study beam evolution and phase-matching conditions inside the waveguide. The experimental results show that the 150-µm capillary achieves higher conversion efficiency around the 27th harmonic when short laser pulses (40 fs) are used. In the 200-µm capillary, argon successfully generates harmonics beyond the traditional atomic cut-off, and helium extends the harmonic wavelength down to 8 nm. These results demonstrate that short laser pulses and proper waveguide conditions are important for phase matching and may enable HHG from highly ionized media.
顯示於類別:	[物理研究所] 博碩士論文

文件中的檔案:

檔案	描述	大小	格式	瀏覽次數
index.html		0Kb	HTML	12	檢視/開啟

在NCUIR中所有的資料項目都受到原著作權保護.

社群 sharing

資料載入中.....