Optical field waveforms synthesis and measurement

光波電場波形合成與量測

詹翰松(Han-Sung Chan)

指導教授 ： 孔慶昌

國立清華大學/電機資訊學院/光電工程研究所/博士(2012年)

https://doi.org/10.6843/NTHU.2012.00102

摘要

如果能夠隨意地產生或量測光波中超快速振盪的電場波形(光波電子學)，即代表著具有控制在埃(10的-18次方)秒時間尺度內電子微觀運動行為的能力，所以發展這種能力變成一個重要的新興科學研究與科技發展的目標。原子尺度下的電子運動行為是許多物理機制的基礎行為，若利用此合成埃秒時間尺度電場波形的能力，來觀測電子微觀動態過程及控制電子動態所造成的物理機制，將會帶來許多好處。光波電場合成器(或光學信號產生器)是一種光波頻域的信號產生器，將會成為一種新的基礎科學儀器，帶給需多領域重要的影響，因此科學上正慎重地發展此能夠合成具有任意埃秒電場形狀的單光週期脈衝的新技術。
在這篇論文中，我們描述我們如何在實驗上成功的合成任意不同形狀的飛秒至次飛秒週期性電場波形。為了產生可以控制載波波包相位的週期性光脈衝，我們利用一道基頻奈秒雷射脈衝產生其倍頻諧波脈衝，接著由分子調製技術，用此兩道脈衝驅動氫氣分子同調性振動，產生多重音階頻寬的光頻梳，此光頻梳合成的脈衝其電場波形的載波波包相位是可以完全控制的。我們利用倍頻與二倍頻干涉儀來量測外差信號，獲得光頻梳內各頻率間的相對相位值，由此證明各頻率間存在鎖相關係以及每發雷射脈衝間載波波包相位的穩定性。我們接著使用此頻率梳中前五個諧波，配合液晶空間光調制器合成電場振盪非弦波形式的光波電場。這些光脈衝中的電場波形的驗證，是利用調制器協助式線性相干法來量測，這是一種利用脈衝調制技術來輔助量測以顯示出電場波形的方法。
我們也發展了一套由非線性光子晶體及聲光調制器構成的光波電場合成器。這套光波電場合成器因為其所有主要的元件都是固態的光學元件，所以可以成為一個更佳方便的小體積光學系統。
因此，我們所發展的兩套光學信號產生器，可提供任意不同形狀的飛秒至次飛秒週期性電場波形，將是未來提供奈米電子、奈米材料、超快電子和化學反應控制等研究領域所需要的一種新科學研究儀器的雛形。

關鍵字

光學波形產生器 ； 光學波形合成 ； 脈衝形變 ； 載波波包相位 ； 光頻梳 ； 波形整形器輔助線性交互相干

並列摘要

Ultrafast optical field waveform generation and measurement (lightwave electronics) affords a capability to attain microscopic control of electronic motion in the attosecond time scale, so it becomes an emerging science and technology of significant impact. The dynamics of electrons in atomic scale is of fundamental physical importance. Investigation of microscopic electronic processes and control of the physical processes enabled by electron dynamics will benefit substantially by having the ability to synthesize and shape electromagnetic field waveforms in the attosecond time scale. The optical field waveform synthesizer, or optical function generator which is a type of function generator in the optical regime, could become a basic and important scientific tool and would have broad impact in many research areas. It is therefore scientifically prudent to develop techniques to synthesize single cycle optical fields (waveforms) of arbitrary shape in the femtosecond to attosecond time frame.
In this dissertation, we describe how we have experimentally synthesized periodic electric field waveforms of various shapes in the femtosecond to subfemtosecond time scale. In order to synthesize periodic pulses whose carrier-envelope phase (CEP) is controllable, we took a nanosecond pulse at a fundamental frequency and generated its second harmonic. We then used the two pulses to drive the vibrational coherence of the hydrogen molecule and produced by molecular modulation a multi-octave spanning harmonic frequency comb that is fully carrier-envelope phase controllable. We employed f-2f interferometry to measure the heterodyne signals and determined the relative phase among the comb components (harmonics), which verified phase-locking among the harmonics and stabilization of the CEP among the pulses from shot-to-shot. We then used the first five harmonics of the comb to synthesize various non-sinusoidal optical field waveforms with the help of a liquid crystal spatial light modulator. These waveforms were verified using shaper-assisted linear cross-correlation, a technique based on pulse-shaping that allows visualization of these phase-stable waveforms.
We have also developed an optical field waveform synthesizer consisting of a nonlinear photonic crystal and an acousto-optical modulator. This system is more compact and convenient because all of the essential components are solid-state.
Hence we have developed two types of optical function generators which are the prototype of a new tool that will provide femtosecond to subfemtosecond periodic electric field waveforms of arbitrary shape for the research community in fields such as nanoelectronics, nanomaterial, ultrafast electronics, and chemical reaction control.

並列關鍵字

optical function generator ； optical waveform synthesis ； pulse shaping ； carrier-envelope phase ； frequency comb ； shaper-assisted linear cross correlation

參考文獻

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