電漿波導X光雷射之先期研發

The preliminary development of x-ray lasers driven in plasma waveguides

蔡海恩(Hai-En Tsai)

指導教授 ： 汪治平

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.00631

摘要

光場游離的X光雷射(< 50 nm)是近年來短波長雷射的一個重要發展方向。它使用體積小,重複率高的飛秒級桌上雷射系統來激發X光雷射的電漿,使其能有效加熱並維持離子態。目前氣態靶的實驗已做到飽和的強度, 接下來在電漿波導中產生X光雷射成為很重要的發展方向。
本篇論文將在第一章介紹X光雷射的發展簡史以及我們的初步成果:首度在氣體噴流中用光場游離與碰撞激發的方式製造出Xe 41.8-nm的X光雷射。實驗中得到接近飽和的輸出。輸出能量高達95 nJ，發散角小於5.2 mrad。使用氣體噴流的好處是不會污染，且適合長期的發展應用。
對這種雷類型的X光雷射來說，居量反轉的生命期只有10 ps的尺度( 這麼短的時間，光只能走1 mm )。所以脈衝必須走縱向來激發增益介質，也就是traveling wave excitation的形式。而如何將X光子放大的電漿體延長一直是重要的課題。為了增加光走的長度並維持在10^16-10^18W/cm^2的強度，有必要導引光的脈衝不發散走好幾倍Rayleigh長度而不發散,也就是波導技術的引入。有鑑於此,我們提出``圓錐透鏡點火加熱方案",分別在氫氣與混合氣體的線性噴流中很高效率地產生電漿波導。其導光效率高達80%以上。成果收編在本論文第二章裡。
本篇論文第三章是關於我們``電漿波導中製造X光雷射"的先期實驗結果與分析。未來我們將在電漿波導中製造出X光雷射，大幅提升此種雷射的效率。並且利用其他種類的原子，邁向更短的波長與飽和輸出。

關鍵字

電漿波導 ； X光雷射 ； 光場游離

並列摘要

In the past few years, there has been considerable interest in using small-scale, high power, femtosecond laser system operating at high repetition rates to generate optical-field-ionization(OFI) plasmas suitable as gain media for collisional excited lasers at xuv wavelengths (< 50 nm). Saturation amplification has been reported by using gas cell targets. In addition, the further development of driving such xuv lasers in plasma waveguides have revealed its potential.
The first chapter of this thesis presents the historic review of xray lasers and the first demonstration of an optical-field-ionization (OFI) x-ray laser with a laser-irradiated xenon clustered gas jet. Near saturated amplification was achieved. The output energy reached 95 nJ, and the divergence angle of which was 5.2 mrad. In comparison with previous OFI x-ray lasers which use gas cell targets, the use of gas jet make contamination-free and long-term operation possible. For xuv lasers of such class, the lifetime of the population inversion is short and so the pumping must be in the form of a traveling wave. This can be achieved most easily by longitudinal pumping. The most serious issue by longitudinal pumping is the formation of a sufficient length of plasma for amplification of xray photons. In order to extend the gain length, it is necessary to guide the pump pulse over many Rayleigh lengths.
In the second chapter, by using the axicon ignitor-heater scheme on a 5-mm slit jet, we successively generated high quality plasma waveguides with significantly improved efficiency of guiding laser pulses with peak intensities relevant to OFI schemes.
The result of a preliminary experiment for OFI x-ray lasers driven in a plasma waveguide is reported and analyzed in the third chapter. Finally, such plasma waveguide will be applied on different ion species to push the OFI lsers toward shorter wavelength and saturation.

並列關鍵字

plasma waveguides ； x-ray lasers ； optical field ionization

參考文獻

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