聲波是一種在日常生活中隨處可聽聞的物理現象，同時也是教科書中用以說明縱波（疏密波，密度波）的典型範例。巨觀而言，雖然我們可以用連續的流體力學方程式來描述它，但是就微觀的原分子尺度或是流體元而言，我們對於微觀粒子的運動細節卻所知有限。粒子在波中運動時，真的只是在原地做簡諧震盪而已嗎？在微粒電漿系統中，微粒聲波可以自發性的生成。因此在本研究中，我們藉由高速光學顯微影像系統觀察微粒聲波，並且分析該波與微粒的交互作用與其動力學，以作為我們對於疏密波這一常見物理現象中，巨觀和微觀圖像的橋樑。 在弱游離的電漿中置入微米大小的顆粒，即可成為所謂的微粒電漿。由於該系統為一強耦合之多體系統，不穩定性與集體之行為在適當的參數調控或是外加驅動下即可產生，前者例如微粒聲波，後者例如脈衝雷射誘發之微粒電漿微泡。微粒聲波在背景壓力低於某一閥值即可自行生成，此為多項不穩定性所導致的自激發結果。藉由分析粒子數量密度的時空演化圖，我們可以看出波動的巨觀行為，例如波長和波速。另外，我們所用的分析方式還包括了計算其空間中功率頻譜的分佈，以及相空間軌跡和延遲時間序列所構成的像空間重構等方法。 至於微觀部份，我們可以追蹤單一微粒於波中的運動行為。我們發現粒子在運動時，會因為撞上微粒聲波的波峰而被攜帶一起前進一段距離或是被其波峰所反彈回去。大多數的粒子在波中並非進行理想之簡諧運動，而是表現出狀似週期性的渾沌運動；而粒子會在不同的波動位能阱中振盪或是躍遷至相鄰的位能阱中。再者，我們可以進一步利用程式同時追蹤所有於波中的粒子，以求得其全體粒子的速度分佈於不同區域中的結果。並且，我們提出一個在移動座標中的洗衣板位能模型，用以解釋上述所觀察到的現象。 除了聲波外，微粒電漿系統也可以產生各種非線性波動。所以在實驗的另一部份，我們利用相同的方法以研究脈衝雷射蒸熔微粒所誘發之微粒電漿微泡（微粒空穴）。電漿微泡可視為一局域化並垂直向下移動的超音速微粒密度波。因此，我們可以進一步的研究當此波穿越微粒聲波時，其所衍生的微粒尾跡場等有趣現象。 Dust acoustic wave (DAW) can be self excited at low pressure in the dusty plasma liquid due to some instabilities. Particle motions are directly observed and analyzed in DAW by a high speed micro image system with suitable illumination. We investigate their interactions and dynamics as a connection between macroscopic and microscopic pictures of the longitudinal wave. Various instabilities and collective behaviors can be self generated, such as DAW, or driven externally such as plasma bubble. In experiments, we can measure the global behaviors of the wave including spatiotemporal evolution of the particle number density, the spatial distribution of the power spectrum, phase space portrait, etc. In microscopic viewpoint, individual particle trajectories are traced in DAW to get its displacement and velocity. It is found that when the particle colliding the wave crest, it may be carried by the wave front and travels together for a short time or it may be repelled by the wave front and turns back. Most particles behave as long time aperiodic or quasi periodic chaotic motion instead of the simple harmonic motion. Particles oscillate in their potential wells may have opportunity to jump to nearby potential wells as the hopping motion. Furthermore, all particle trajectories are traced at the same time to study the velocity distribution of the particles in the wave. In another part of the experiment, the same methods are used to observe the spatiotemporal evolution and particle dynamics for pulsed laser ablation induced plasma bubble, i.e., spherical dust cavity. The collapsing plasma bubble can be considered as a downward propagating supersonic dust shock wave. Consequently, we further investigate some interesting phenomena such as the wave-bubble interactions and the induced dust wake field behind the bubble when plasma bubble traveling through DAW.
