局域性銀奈米粒子表面電漿共振硒硫化鎘/硫化鋅產生隨機雷射之研究
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2016
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Abstract
本研究主要探討藉由調控輻射發光電場震盪方向與橢圓銀奈米粒子局域性表面電漿共振(localized surface plasmon, LSP)間的耦合強度，來達到具有高同調性(coherent)與高光學異象性(optical anisotropy)的硒化鎘/硫化鋅(CdSe/ZnS)膠狀量子點(colloidal quantum dots, CQDs)隨機雷射 (random laser)。迥異於傳統CdSe/ZnS CQDs只能觀察到放大自發輻射(amplified spontaneous emission, ASE)，我們所提出的隨機雷射結構其雷射出射光譜展現清楚的干涉特性(spectral spikes)以及較低的雷射閥值特性(low threshold pumping power)—主要歸因於橢圓銀奈米粒子周圍因LSP共振效應所誘發出高光散射(optical scattering)以及高光增益(optical gain)等特性。更重要的是，我們發現硒化鎘/硫化鋅量子點其輻射發光電場震盪方向與橢圓銀奈米粒子主軸之相對位置，可以選擇性地激發LSP 共振，此對於隨機雷射之特定光學極化輸出，佔有極重要角色。我們也進一步的使用時域有限差分法(Finite-Difference Time-Domain, FDTD)來探討與驗證CdSe/ZnS CQDs輻射發光之電場震盪方向與橢圓銀奈米粒子主軸間的相互物理關係。最後，藉由旋轉塗布與控制銀奈米粒子的幾何形狀，我們即能同時達成局域性表面電漿共振與硒化鎘/硫化鋅膠狀量子點輻射發光在空間中與在光譜上的高重合度。這也說明了本論文所提出的架構，是個簡單、可行但同時具有高前瞻性。其可以克服傳統量子點因歐傑復合(Auger Recombination)效應不易產生誘發輻射的缺點，進而實現以量子點為基礎之具有高同調性、低閥值特性以及特定光學極化的新穎隨機雷射。
We demonstrate the capability of controlling the optical anisotropy of lasing emissions by manipulating the coupling strength between the oscillating electric field of emitted light and the localized surface plasmon (LSP) resonance in a random lasing medium composed of colloidal CdSe/ZnS quantum dots (QDs) and ellipsoidal silver nanoparticles (Ag NPs). Distinctive from the amplified spontaneous emission (ASE) generally observed on the colloidal CdSe/ZnS QDs, it is found that lasing emissions of the revealed system exhibits clear interference features (coherent optical feedbacks) with low-threshold characteristics, mainly attributed to enhanced light scatterings and optical gains arisen in the peripheral surfaces of ellipsoidal Ag NPs. Importantly, the relative orientation, between the oscillating electric field of emitted light from colloidal CdSe/ZnS QDs and the major axis of ellipsoidal Ag NPs, plays a critical role in selective excitation of LSP resonances to promote laser emissions with specific optical polarizations. That is further examined and verified by the finite-difference time-domain (FDTD) simulation. The unique and manipulating properties, associated with the LSP resonance coupling effect of ellipsoidal Ag NPs, make the present system as promising candidates for achieving coherent and polarized lasing emissions based on the colloidal semiconductor quantum dots.
We demonstrate the capability of controlling the optical anisotropy of lasing emissions by manipulating the coupling strength between the oscillating electric field of emitted light and the localized surface plasmon (LSP) resonance in a random lasing medium composed of colloidal CdSe/ZnS quantum dots (QDs) and ellipsoidal silver nanoparticles (Ag NPs). Distinctive from the amplified spontaneous emission (ASE) generally observed on the colloidal CdSe/ZnS QDs, it is found that lasing emissions of the revealed system exhibits clear interference features (coherent optical feedbacks) with low-threshold characteristics, mainly attributed to enhanced light scatterings and optical gains arisen in the peripheral surfaces of ellipsoidal Ag NPs. Importantly, the relative orientation, between the oscillating electric field of emitted light from colloidal CdSe/ZnS QDs and the major axis of ellipsoidal Ag NPs, plays a critical role in selective excitation of LSP resonances to promote laser emissions with specific optical polarizations. That is further examined and verified by the finite-difference time-domain (FDTD) simulation. The unique and manipulating properties, associated with the LSP resonance coupling effect of ellipsoidal Ag NPs, make the present system as promising candidates for achieving coherent and polarized lasing emissions based on the colloidal semiconductor quantum dots.
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同調隨機雷射, 局域性表面電漿共振, 膠狀量子點, 偏振發光, Coherent Random Laser, Localized Surface Plasmon Resonance, Colloidal Quantum Dots, Polarized Emissions