量子點光源之二次相關性

Abstract

本論文中Hanbury Brown Twiss實驗系統已被架設，並用此系統量測兩種量子點樣品光子輻射的二次相關性函數g(2)(τ)。被限制在金屬光窗的單一量子點存在明顯的反群聚效應，其在低注入雷射功率的狀況下，有最小的g(2)(0)值為0.298，接近理想的單光子源，當持續增加注入雷射功率時，因為背景雜訊增加及反群聚時間下降，g(2)(0)值上升；另一個量子點放置在微柱共振腔內的樣品，當量子點激子態與共振腔模態雷射產生共振時，顯現出Purcell effect而增加量子點的自發輻射效率，令人感到有趣地，當持續增加注入雷射功率時，量子點與共振腔模態耦合輻射從反群聚效應(g(2)(0)<1)轉換成群聚效應(g(2)(0)>1)，對於雷射閥值而言，此轉換過程較一般的強度分析方法更為靈敏，所以量測二次相關性函數可用來檢驗零閥值雷射的閥值。

In the thesis, the system of Hanbury Brown- Twiss(HBT) experiment has been setup and tested by measuring the second order correlation function (g(2)(□)) of photons emitted by two quantum dot (QD) simples. Single quantum dots defined with metal mask exhibit clear anti-bunching behavior. The obtained lowest g(2)(0) is about 0.298 at low excitation power. With increasing pumping power, g(2)(0) increases because of increased background noise and reduced anti-bunching time. The other sample, single QDs placed in micro-pillar cavity, shows significant Purcell effect when the resonance between excitonic states of QD and cavity modes occurs. Interestingly, with the increasing pumping powers, the emission of single QDs resonant with cavity mode shows a transition from the anti-bunching behavior (g(2)(0) < 1) to bunching behavior (g(2)(0) > 1). This transition is more sensitive than the conventional methods so the measurement of g(2)(□) can be used to determine the threshold value of threshold-less lasers.