邊界效應對高階雷射模態之產生和雷射激發水柱之噴濺的影響

Abstract

本文的第一部分，利用半導體雷射VCSEL類比研究橫向邊界下的橫向高階模態，並且從近場至遠場的觀察，研究橫向模態出光的特性和方向性。相較於微腔體發光元件之出光特性的研究，利用VCSEL可以更直接的觀察到其模態的空間演進。從研究結果中，我們證明了近場橫向模態和出光的方向性並非絕對一對一的關係。當近場橫向模態有著圖像上顯著的差異，其遠場仍有可能具有大致相同的方向性。更進一步，我們藉由量子彈子球檯的模型和近軸光學的繞射來理論分析觀察到的實驗結果。 第二部分，我們對雷射激發水柱之噴濺的形成作了深入的研究。將雷射垂直聚焦入射於水面之下，利用高速攝影觀察水面上之噴濺的行為，並針對其結構和形成機制做了細節的探討。在水柱於空間行進的演化中，水柱中間會產生一個氣泡，並且在適當的雷射聚焦深度下，此氣泡中會包含一顆水滴。此外，由於雷射產生的電漿具有很大的動能平行於入射方向，因此當我們將雷射水平入射聚焦於水中時，水面的噴濺將不再是柱對稱結構，具有平面結構的特徵變化。

In this work, we investigate the high-order laser modes by a large-aperture VCSEL in different shapes of transverse confinement. VCSELs bear the potential to allow for directly observing the transverse modes and its free space propagation. Additionally, the light emitted from VCSEL is meaningful for studying the time diffraction from a high-order quantum mode. The experiment is reconstructed very well by theories of quantum billiard and Fresnel diffraction. We show that the far-field directional emission from a microcavity is just a necessary not sufficient condition for the emergence of a superscar mode. In next part, we investigate the laser-induced liquid jet. A pulsed laser is vertically focused into a tap water to induce a water jet on a flat water surface. The water jet is observed by a high speed camera and the mechanism is discussed in detail. In the temporal evolution of the water jet, there is an air bubble with a water drop inside formed in the water jet. Additionally, we horizontally focus the laser beam into the water and observe the water jet. This water jet shows a sheet features.