臺灣博碩士論文加值系統

在強場物理實驗，例如電子加速器、軟X 光雷射、及高階諧波的
產生，增長高強度雷射脈衝與物質交互作用的空間往往是關鍵


我們採用雷射電漿波導的方式並結合圓錐透鏡聚焦與點火-加熱脈衝的方案
來產生電漿波導。使用圓錐透鏡的目的在於使雷射光聚焦成1-2cm 的線聚
焦。「點火-加熱方案」的優點在於有效利用雷射脈衝的能量來游離並加熱
電漿；高強度的點火脈衝先游離出自由電子，高能量的加熱脈衝再繼續加
熱電子並利用碰撞機制游離出更多電子，一段時間後會演化成中間凹陷的
電子密度分佈，其所對應到的電漿折射率具有聚焦特性，可將注入的雷射
脈衝以聚焦形式傳遞而不致發散。
在這次實驗中，我們利用氫氣及1cm 的線性噴嘴來產生氣體噴流。但
實驗發現，因氣體噴流中的原子密度不夠，沒有足夠的電子來形成電漿波
導。為了提高原子密度，我們使用低溫冷卻氣流閥的技術，利用液態氮將
氣流閥冷卻到低溫來提高氣體噴流的密度。實驗證明，我們將氣流閥冷卻
到123K 時，氫氣噴流的原子密度增為室溫的2.5 倍。同時有效的產生電
漿波導。其導光效率高達66%。未來我們將會應用此技術到電子加速器上，
藉由1cm 的電漿波導來達到高能電子的輸出。

To extend the interaction length in laser-plasma interaction is the key
factor to the success of many important applications, such as the
laser-driven electron accelerator, soft x-ray laser, and high harmonic
generation. In our experiment, we generate an elongated plasma waveguide
by using a combination of an axicon and the ignitor-heater scheme. The
axicon is a lens in a cone shape which can be use to focus the incident light
into a line focus. The ignitor-heater scheme consists of a short and a long
laser pulses to produce and heat electrons efficiently. To produce a plasma
waveguide, an intense short pulse is focused into the gas to generate the
seed electrons via field ionization, and a copropagating high-energy long
pulse arrives later to heat the plasma and drive the hydrodynamic
expansion. After an adequate time, the plasma waveguide is formed
through the hydrodynamic evolution of the laser-produced plasma in gases.
Since the electron density produced from the hydrogen gas jet with a
1-cm slit nozzle is too low to efficiently form plasma waveguide, a method
to increase the atom density of hydrogen is necessary. A cryogenic system
filled with liquid nitrogen is used to cool the valve and gas reservoir of the
gas jet to increase the local atom density. When the temperature of the gas
jet is reduced to 123K, the atom density of hydrogen is found to be 2.5
times higher than the room temperature, and a plasma waveguide is
efficiently generated with a guiding efficiency of 66%. The high-efficiency
plasma waveguide may soon be applied to electron accelerator to produce
high-quality and high-energy electron beams.

目錄
摘要 i
Abstract ii
致謝 iv
1. 緒論
1.1 各種電漿波導技術簡介 1
2. 在線性氣體噴流中產生電漿波導
2.1 電漿波導的基本原理 4
2.2 電漿波導的導光條件 8
2.3 利用低溫冷卻系統增加氣體密度 10
3. 實驗設計與架設
3.1 雷射系統簡介 12
3.2 以圓錐透鏡製造線聚焦 15
3.3 實驗設計與架設 19
3.4 觀測系統-干涉儀 22
3.5 氣體噴流系統 24
3.6 低溫冷卻系統 26
4. 實驗結果與討論
4.1 電漿波導隨各參數的變化 27
4.2 低溫冷卻系統使用注意事項 33
4.3 未來發展 34
參考文獻 35

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