可調式隨機雷射與熱膨脹係數之研究

Study on flexible random lasers with tunable lasing emissions and thermal expansion coefficients

周俊仰(Chou Chun-Yang)

指導教授 ： 李亞儒

國立臺灣師範大學/理學院/光電科技研究所/博士(2018年)

https://doi.org/10.6345/DIS.NTNU.EPST.019.2018.E08

摘要

本研究分為兩個部分。1.可調式隨機雷射、2.使用光學斷層掃描測定大功率InGaN基板發光二極體的熱膨脹係數。
在研究中，我們通過實驗證明了在聚對苯二甲酸乙二醇酯（PET）基材上製造的可調式隨機雷射，其雷射發射具有高度的可調性。隨機雷射振盪主要來自增益介質（羅丹明6G，R6G）發射光子與銀奈米稜鏡（Ag NPRs）的局域表面電漿（LSP）之間的共振耦合，這增加了多光散射的有效截面，從而刺激雷射發射。
更重要的是，隨機振蕩波長隨著施加在PET基材上彎曲應變的增加而藍移，並且在彎曲應變為50％時雷射波長實現了約15nm的最大偏移施加在PET基材上。這種觀察是高度可重複的和可逆的，並且這證明我們可以通過簡單地彎曲用Ag NPRs裝飾的可調基底來控制雷射波長。使用顯微鏡測量AgNPRs的散射光譜以了解波長漂移對施加的彎曲應變依賴性的機制。因此，我們相信基於顯示結構的可調式雷射發射的實驗性展示，有望開創隨機雷射的新應用領域。
熱膨脹係數（CTE）是指加熱時材料的熱膨脹值的物理量。對於先進的熱管理，由於對高功率發光二極體（LED）的需求正在增加，所以準確和即時確定包裝材料的CTE正變得越來越重要。在這項研究中，我們使用光學相干斷層掃描（OCT）來測量封裝在聚苯乙烯樹脂中的InGaN基板（λ= 450 nm）高功率LED的CTE。觀察和記錄OCT圖像的各個界面之間的距離，以導出在不同註入電流下封裝LED的瞬時CTE。順向電壓法建立了不同注入電流下的LED結溫。因此，測得的聚苯乙烯樹脂的瞬時CTE在25-225℃的結溫範圍內從5.86×10-5℃-1變化到14.10×10-5℃-1，並且在OCT掃描區域中呈現均勻分佈200微米×200微米。最重要的是，這項工作證實了OCT可以提供一種替代方法來直接和非破壞性地確定封裝LED器件的空間分辨CTE的假設，並提供了優於傳統CTE測量技術的顯著優勢。

關鍵字

隨機雷射 ； 銀奈米稜鏡 ； 局域表面電漿 ； 彎曲應變 ； 熱膨脹係數 ； 光學相干斷層掃描

並列摘要

The study is divided into two parts. 1. Flexible random lasers with tunable lasing emissions. 2. Determination on the Coefficient of Thermal Expansion in High-Power InGaN-based Light-emitting Diodes by Optical Coherence Tomography.
In this study, we experimentally demonstrated a flexible random laser fabricated on the polyethylene terephthalate (PET) substrate with a high degree of tunability in lasing emissions. Random lasing oscillation arises mainly from the resonance coupling between the emitted photons of gain medium (Rhodamine 6G, R6G) and the localized surface plasmon (LSP) of silver nanoprisms (Ag NPRs), which increases the effective cross-section for multiple light scattering, thus stimulating the lasing emissions.
More importantly, it is found that the random lasing wavelength is blue-shifted monolithically with the increase in bending strains exerted on the PET substrate, and a maximum shift of ~15 nm was achieved in the lasing wavelength, when a 50% bending strain was exerted on the PET substrate. Such observation is highly repeatable and reversible, and this validates that we can control the lasing wavelength by simply bending the flexible substrate decorated with the Ag NPRs. The scattering spectrum of the Ag NPRs is measured using a dark-field microscope to understand the mechanism for the dependence of wavelength shift on the exerted bending strains. As a result, we believe that the experimental demonstration of tunable lasing emissions based on the revealed structure is expected to open up a new application field of random lasers.
The coefficient of thermal expansion (CTE) is a physical quantity that indicates the thermal expansion value of a material upon heating. For advanced thermal management, the accurate and immediate determination of the CTE of packaging materials is gaining importance because the demand for high-power lighting-emitting diodes (LEDs) is currently increasing. In this study, we used optical coherence tomography (OCT) to measure the CTE of an InGaN-based (λ = 450 nm) high-power LED encapsulated in polystyrene resin. The distances between individual interfaces of the OCT images were observed and recorded to derive the instantaneous CTE of the packaged LED under different injected currents. The LED junction temperature at different injected currents was established with the forward voltage method. Accordingly, the measured instantaneous CTE of polystyrene resin varied from 5.86 × 10-5 °C-1 to 14.10 × 10-5 °C-1 in the junction temperature range 25–225 °C and exhibited a uniform distribution in an OCT scanning area of 200 μm × 200 μm. Most importantly, this work validates the hypothesis that OCT can provide an alternative way to directly and nondestructively determine the spatially resolved CTE of the packaged LED device, which offers significant advantages over traditional CTE measurement techniques.

並列關鍵字

Random laser ； Silver nanoprism ； Localized surface plasmon ； Bending strain ； Coefficient of thermal expansion ； Optical coherence tomography

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