具共振週期增益複雜化合物半導體結構之光電研究

Abstract

本計劃為一新提三年計劃，我們將繼續探討光與物質之交互作用，特別是複雜垂直共振腔具有半導體共振週期增益(resonant periodic gain RPG)結構中之量子交互作用。與先前最大之不同是我們將設計研究更為複雜之光電半導體共振腔系統，已期更了解其作用機制，並達成更佳之光場操控。 我們將先投入長晶設計及製作另一種半導體雷射，亦即光激垂直外腔式半導體雷射(Vertical External Cavity Surface Emitting Laser VECSEL)，此種雷射共振腔採用垂直外腔設計及半導體共振週期增益。我們初步已成功製作出 2.35W高平均功率 778 fs 脈沖寬，重複率達2.17 GHz之光激半導體雷射。 因為VECSEL共振腔係採用複雜之共振週期增益結構(resonant periodic gain RPG)，又與半導體DBR鏡面結合，故長晶困難度增加許多。而雷射係採用外架之輸出鏡，使得調控之參數增加了許多變化。我們也同時發現雷射臨界激發功率與輸出鏡反射率之特性與習知者不同，在使用另一鏡面做成耦合輸出鏡之後，半導體雷射之調控變成極為容易，且雷射之輸出更易達到最佳化之狀態。此現象均與半導體增益介質具擴散流動性有關，故其動態機制亦為研究重點。凡此種種均讓我們發現此系統更適於研究量子彈子球台物理及量子光學CQED。因此新的計畫將全力投入此種VECSEL之長晶設計與雷射調控之研究，進而以此投入探討基本之半導體增益介質動態機制或更為實用之超快雷射之應用研發。

In this three-year proposal, we will still study the interaction between light and matter semiconductor quantum well exiciton, particularly the cavity quantum electrodynamics (CQED) in complex semiconductor vertical external cavity laser structure. With the new complex laser structure, we will have much better control of the optical field and a thorough understanding of the interaction mechanism can be expected. We will design, grow and fabricate a new type of semiconductor vertical cavity laser i. e. optically pumped vertical external cavity surface emitting Laser (VECSEL). This type of laser employs a vertical external optical cavity and resonant periodic gain in the design. We have preliminarily achieved a VECSEL with an average power of 2.35W, mode locked pulse width of 778 fs and repetition rate of 2.17 GHz. It is a self mode locked femto second laser and the self mode locking mechanism is still being investigated. Since VECSEL employs resonant periodic gain ( RPG) structure and DBR mirror, the more complex epitaxial structure makes the crystal growth more demanding. However the external output coupler mirror design makes the laser adjustment more flexible and a lot of more variations in the laser system can be realized. We have noticed that a coupled cavity setup in the output coupler makes the laser adjustment much more easily. Optimization of the laser output power and laser beam quality can be easily obtained. All these phenomena are speculated to be related to the diffusion of the optically excited semiconductor carriers, and the carrier dynamics will be fully investigated. With all these preliminary results, we have confidence that VECSELs are worthy devices for us to devote into and a lot more scientific study in coherent physics and ultra fast laser physics can be investigated.