臺灣博碩士論文加值系統

對於產生同調軟 X 射線激光在水窗區域,我們計劃聚焦主要激光在高原子數離子的介
質,產生高階諧波。高階諧波產生的效率被主要激光和高階諧波的相位不批配限制。在反相
位的高階諧波區域的電場和正相位的高階諧波的區域的電場會相消干涉,使高階諧波產生的
效率強度不能建設性增加。然而,強度相對較弱的(1/100)反方向對撞激光可以破壞高階
諧波產生在反相位的範圍。因此,我們建立雙色的激光放大系統,構建一個可控脈衝間隔時
間 的拍波脈衝序列,以對應準相位匹配條件使高階諧波可以建設性增加產生。
雙色激光放大系統是 100-TW 激光系統的分支。它的中心波長為 800 nm。首先,它被
是聚焦於充滿氪氣的長管中產生超連續光譜的產生。由於自相位調製,它可擴展頻譜到 900
nm。在那之後,我們送它進聲光調變器過濾為兩個尖峰的光譜。隨後,它進入到脈衝延展器
的時間把時間延展從 50 fs 到 50 ps。最後,它通過第一級放大器和第二級放大器來放大
能量。在脈衝壓縮器中,我們可以壓縮成短的脈衝時間和調整屋頂鏡延遲線在脈衝壓縮器中,
使雙色波的時間重疊間並形成拍波序列脈衝串。
在那之後,我們要實驗這雙色激光系統可以構建我們想要的脈衝串。在這裡,我們用
20-TW 激光作為探針波與拍波在 BBO 上交叉產生和頻(SFG)。我們可以調整探測波延遲線來
做互相關實驗。
最後,在 600 fs 的脈衝串可以觀察到近 10 個清晰的脈衝。該脈衝間隔時間恰好對應
高階諧波準相位匹配條件。

For generating coherent soft x-ray laser in the water window region, we plan to
focus driving laser on the high-Z ions as interacting medium to generate high-
harmonic generation. The efficiency of high-harmonic generation is limited by the
phase-mismatch of driving laser and high-harmonic generation. The out-of phase
high-harmonic generation field and in phase high-harmonic generation field cause
destructive interference so that the efficiency of high-harmonic generation intensity
can not constructively increase.
However, a relatively weak intensity (1/100) counter-propagating laser can disrupt
the high-harmonic generation emission from the out-of phase range. Therefore, we
build the two-color laser amplifier system to construct a beat-wave pulse train with
controllable pulse separation time to fit quasi-phase-matching condition of high-
harmonic generation.
The seed laser of the two-color laser amplifier system is from the 100-TW laser
system branch. The center wavelength is 800 nm. First, it is focused on a long tube
full of Kr gas to generate supercontinuum generation. The spectrum can be extended
to 900 nm due to self-phase modulation. After that, we send it into Dazzler to filter
the spectrum into two peaks. Then, it goes to stretcher to stretch the duration from
50 fs to 50 ps. After all, it gains energy through first-stage amplifier & second-
stage amplifier. In the compressor, we can compensate the dispersion of chirp pulse
to compress it into short pulse duration and adjust roof mirror delay line in the
compressor to make two color waves temporal overlap and form beat-wave pulse
train.
After that, we want to examine that this two-color laser system can construct the
pulse train we want. Here, we use 20-TW beam line as a probe wave to cross
with beat-wave on BBO crystal generating sum-frequency generation (SFG). We
can adjust the delay line of probe wave to do the cross-correlation experiment.
Finally, these are nearly 10 clear pulses being obtained in a 600-fs pulse train. The
separation time of pulses just fit quasi-phase-matching condition of high-harmonic
generation.

Contents
1 Introduction and Motivation 1
1.1 Introduction of High-Harmonic Generation . . . . . . . . . . . . . . . 1
1.2 HHG Phase-Mismatching Problem . . . . . . . . . . . . . . . . . . . 3
1.3 Quasi-Phase-Matching Method (QPM) . . . . . . . . . . . . . . . . . 5
1.3.1 Selective-Zoning Quasi-Phase-Matching Method . . . . . . . . 6
1.3.2 Beat-Wave Pulse Train for QPM . . . . . . . . . . . . . . . . 8
2 Two-Color Laser Amplifier System 11
2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2 Two-Color Laser Amplifier System Layout . . . . . . . . . . . . . . . 11
2.3 Supercontinuum Generation . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.1 Self-Phase Modulation (SPM) . . . . . . . . . . . . . . . . . . 13
2.3.2 Simulation of SPM . . . . . . . . . . . . . . . . . . . . . . . . 15
2.3.3 The Stability of WLG & Supercontinuum Generation . . . . . 17
2.3.4 Acousto-optic Programmable Dispersive Filter (Dazzler) . . . 21
2.4 First-Stage Amplifier & Second-Stage Amplifier . . . . . . . . . . . . 22
2.5 Compressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3 Characterization of the Beat-Wave Pulse Train 29
3.1 Experiment Setup & Layout . . . . . . . . . . . . . . . . . . . . . . . 29
3.2 Experiment Flowing Chart . . . . . . . . . . . . . . . . . . . . . . . . 30
3.3 Beat-Wave Waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.4 Conclusion and Prospect . . . . . . . . . . . . . . . . . . . . . . . . 40
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