光子晶體雷射之近場光學影像分析

Abstract

本論文利用近場光學顯微技術探討光子晶體產生雷射的空間分 布。首先藉由變功率微螢光激螢光光譜量測探討D0結構光子晶體雷射中缺陷模態的輸入輸出曲線、波長以及半高寬變化關係。激發功率增加時，會使得缺陷模態訊號增強，半高寬變窄及波長藍移。接著利用變功率全譜線近場光學掃描量測，可釐清光子晶體產生雷射過程時光強度、半高寬及波長的空間分布，並藉此分析雷射產生的區域。當激發功率超過臨界功率後，光激載子會藉由受激輻射轉換成光子，使載子濃度維持動態平衡。藉由高於臨界功率激發的近場掃描中的波長分布則可判斷臨界載子空間分布的情形。最後探討雙重模態同時存在的雷射特性。藉由變功率微光激螢光光譜及近場顯微技術的量測，可觀察到兩種模態在空間中相互競爭的效應。

Lasing characteristics of photonic crystal nanocavity are investigated by micro-photoluminescence (micro-PL) and scanning near-field microscopy (SNOM) measurements. First, the optical process of lasing characteristics including intensity, wavelength and linewidth are investigated by power-dependent micro-PL measurements. With increasing excitation power , the modes intensity increasing, linewidth narrowing and wavelength blue shift are observed. The spatial distribution of lasing characteristics are investigated by spectral resolved SNOM measurements. The spatial distribution of modes intensity and linewidth can be used to identify the lasing area. When excitation power exceeding the lasing threshold , photo- excited carriers are converted rapidly into photons due to stimulated emission, and therely pinning the carrier concentration. The spatial distribution of threshold carrier density can be revealed by lasing wavelength distribution when using above threshold excitation power. Finally, we observe spatial excitation mode competition in dual-mode laser under different powers.