新穎奈米雷射之開發與應用
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2020
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近年來，隨著基礎科學的研究與發展，帶動了科學及技術的進步，雷射技術也得以迅速的發展，是由於雷射光束具有發散度極小、亮度（功率）很高、單色性好、相干性好等光學特性，因此在許多方面獲得了廣泛的應用，在工業上的雷射割切、加工、掃描、雷射雷達、雷射干涉儀，或是醫學上應用在外科手術、止血、去除色斑和修正視力，是邁向人類提高生活品質不可或缺的重要利器。而且雷射的單色性及極短脈波等，也成為發掘物質新特性的有利工具，在物理、化學、生物醫學等方面的貢獻可謂日益重大，所以新雷射的技術開發也是重大的挑戰。
傳統雷射需要由兩面反射鏡組成共振腔，使增益介質在共振腔中累積足夠的光子，當達到居量反轉時輸出雷射光，所以通常體積大、製作不易且成本高，且光的散射會不利於雷射光的產生，因為光散射會造成損耗，而散射越強損耗就越大。反之，對於隨機雷射來說，光散射為產生隨機雷射的重要因素。利用隨機排列的散射介質來形成類似共振腔的封閉散射路徑，激發光則藉由這些封閉迴路產生多重散射。一旦平衡了系統中的淨增益和總損耗，可以在幾個方向上觀察到隨機激光發射。隨機雷射製成簡單、成本低且體積小，因此適合應用在許多領域上。像是遠程傳感器、雷射成像、醫療檢測、穿戴式感測器、顯示器或照明等等。另外我們也開發垂直共振腔面射型雷射，由於其表面法線發射、靈活的封裝能力和良好的光束質量，因此在光電技術和工業中被廣泛採用。此外，可以通過設計光學增益材料的能隙和面射型雷射腔內的諧振頻率來實現光譜發射的可調性和雷射模態選擇性。垂直腔面發射激光器是一種獨特的光源，可提供廣泛的應用，例如3D傳感、高速數據通信和雷射顯示器等等。本論文依照各個章節不同的研究主題和使用方法將摘要進行分類，其分類如下：
1. 曲率調控之隨機雷射
由於沒有明確的共振腔，因此限制了隨機雷射的應用，因為隨機雷射主要取決於由散射介質引起的多重光散射產生的封閉迴路，從而增加了控制難度。為了有效地調節隨機雷射，在本文中，使用水熱法成長氧化鋅奈米柱組成的無序散射體，並使用羅丹明 6G（Rhodamin 6G）作為增益介質，透過Nd：YAG脈衝雷射激發來產生隨機雷射（random laser）。光子的傳輸平均自由路徑（mean free path, MFP）可以通過彎曲下方的聚對苯二甲酸乙二醇酯（PET）柔性基板來調節曲率，從而創建可在閥值上下操作的獨特光源。此外，我們首次通過簡單的機械彎曲，將開發的曲率可調控隨機雷射用於體內生物成像，與無產生隨機雷射時的情況相比，具有更低的散斑噪聲，這對於研究快速移動的生理現象（例如老鼠耳朵皮膚中的血流模式）。曲率可調控隨機雷射的實驗可以預期成為開發基於無序的光電元件提供一條新途徑。本篇論文研究成果已投稿於Nanoscale (10.1039/c8nr09153f)。
2. 光學應變感測隨機雷射
本研究利用閥值可調式隨機雷射來製作高靈敏度可撓曲應變感測器，透過將隨機雷射元件成長於聚酰亞胺（PI）柔性基板上，利用氧化鋅奈米柱組成的無序散射體，激發增益介質羅丹明 6G（Rhodamin 6G）產生隨機雷射。通過在柔性基板上施加應力，使基板彎曲來演示光譜發射的可重複性和可逆調整性，這使我們能夠在低於或高於雷射閥值的情況下激發隨機雷射。此外，我們的隨機雷射在彎曲應變為 40% 的情況下，可作為穩定耐用的光學應變器，其應變係數約為 37.7 5.4，藉由低溫簡單製成的方式製作光學檢測的應變感測器，可媲美傳統的電應變感測器。這項研究證實了隨機雷射光學應變感測器可以用於各個管路、橋梁等監控，也可製作成穿戴式感測器，在這些領域中，電錶受到限制並且光學量測被認為是更好的替代方案。本篇論文研究成果已投稿於APL Materials (10.1063/1.5099316)。
3. 石墨烯量子點垂直共振腔面射型雷射
石墨烯量子點（GQDs）是一種新穎光學增益材料，其優異的溶液特性可用於製作高效率元件成為新光源。迄今為止，只有極少數關於GQDs產生雷射的研究。在本論文中，我們是第一個成功地製作出室溫光激發石墨烯量子點綠光面射型雷射的團隊。由Ta2O5 / SiO2兩種高折射係數差異的介電質材料做週期性堆疊成長，並設計製作布拉格反射鏡（Distributed Bragg Reflector, DBR），同時提供GQDs在光譜上的寬截止區，且在紫外光區域也具有高穿透率。藉由本實驗清楚地證明了GQDs能作為一種實用、成本低廉且高量子轉換效率的光學增益材料，展現GQD-VCSEL在寬色域雷射顯示器和投影式影像的潛在應用邁出的重要一步。本篇論文研究成果已投稿於ACS photonics (10.1021/acsphotonics.9b00976)。
In recent years, with the research and development of basic science, which has promoted the progress of science and technology, laser technology has also been developed rapidly. The laser beam has some good optical characteristics such as a very small divergence, high brightness (power), good monochromaticity, coherence light and so on. So laser have been widely used in many aspects, such as industrial laser cutting, processing, scanning, laser radar, laser interferometer, or medical application in surgery, hemostasis, removal of stains and correction of vision are important and indispensable tools for improving the quality of life of human beings. In addition, the monochromaticity of lasers and extremely short pulse waves have also become useful tools for discovering new properties of matter. Contributions in physics, chemistry, biomedicine, etc. can be described as increasingly important, so the development of new laser technology is also a major and eternal challenge. The traditional laser requires a two-sided reflector to form a resonant cavity, so that the gain medium accumulates enough photons in the resonant cavity, and laser light output when it reached the population inversion. Therefore, it is usually bulky, difficult to manufacture and costly. Conversely, for a random laser, it is important to generate a random factor in the laser light scattering. A randomly arranged scattering medium is used to form a closed scattering path similar to a resonant cavity, and excitation light generates multiple scattering through these closed loops. Once equilibrated the net gain of the system and the total losses, random laser emission canbe observed in several directions. Random lasers are simple, low cost, and small, making them suitable for many applications. Things like remote sensors, laser imaging, medical inspections, wearable sensors, displays or lighting, and more. In addition, we have also developed vertical cavity surface emitting lasers, which are widely used in optoelectronic technology and industry due to their surface normal emission, flexible packaging capabilities, and good beam quality. In addition, the tunability of spectral emission and laser mode selectivity can be achieved by designing the energy gap of the optical gain material and the resonance frequency in the surface-emitting laser cavity. Vertical cavity surface emitting lasers are a unique light source that can provide a wide range of applications, such as 3D sensing, high-speed data communications, and laser displays. This paper categorizes abstracts according to different research topics and methods of use in each chapter. The classification is as follows: 1. A Curvature-Tunable Random Laser The application of random lasers has been restricted due to the absence of a well-defined resonant cavity, as the lasing action mainly depends on multiple light scattering induced by intrinsic disorders of the laser medium to establish the required optical feedback that hence increases the difficulty to efficiently tune and modulate random lasing emissions. This study investigated whether the transport mean free path of emitted photons within disordered scatterers composed of ZnO nanowires is tunable by a curvature bending applied to the flexible polyethylene terephthalate (PET) substrate underneath, thereby creating a unique light source that can be operated above and below the lasing threshold for desirable spectral emissions. For the first time, the developed curvature-tunable random laser is implemented for in vivo biological imaging with much lower speckle noise compared to the non-lasing situation through simple mechanical bending, which is of great potential for studying fast-moving physiological phenomenon such as blood flow patterns in a mouse ear skin. It is expected that the experimental demonstration of the curvature-tunable random laser can provide a new route to develop disorder-based optoelectronic devices. The research results of this paper have been submitted to Nanoscale (10.1039 / c8nr09153f). 2. A Strain-Gauge Random Laser We describe a random laser that uses the ZnO nanorods (NRs) randomly orientated on a flexible polyimide (PI) substrate as disorderedly optical scatterers to stimulate coherent random lasing actions. Repeatable and reversible tuning of spectral emission is demonstrated by exerting a bending strain on the PI substrate, which enables us to activate the random laser on either below or above the lasing threshold. Furthermore, our random laser functions as a stable and durable optical strain gauge with a gauge factor of ≈37.7 5.4 under a bending strain of 40%, which is comparable to that of traditional electrical strain gauges. The study validates that the reported strain-gauge random laser is able to be used in certain fields where the electrical gauge is restricted and the optical gauge is considered to preferable as an alternative solution. The research results of this paper have been submitted to APL Materials (10.1063 / 1.5099316). 3. Graphene Quantum Dot Vertical Cavity Surface Emitting Lasers Nonzero-bandgap graphene quantum dots (GQDs) are novel optical gain materials promising for solution-processed light sources with high cost efficiency and device performance. Herein, we demonstrate for the first time room-temperature lasing emission with green gamut from GQDs in a vertical optical cavity composed of Ta2O5/SiO2 dielectric distributed Bragg reflectors (DBRs). The lasing is enabled by the unique design of the DBR which not only provides a wide stopband spectrally overlapping with the emission of the GQDs but also allows high transmittance of optical excitation in the UV-light region. This demonstration is a clear evidence of the use of GQDs as optical gain materials and represents an important step forward toward their potential applications in wide-gamut laser displays and projectors. The research results of this paper have been submitted to ACS photonics (10.1021 / acsphotonics.9b00976).
In recent years, with the research and development of basic science, which has promoted the progress of science and technology, laser technology has also been developed rapidly. The laser beam has some good optical characteristics such as a very small divergence, high brightness (power), good monochromaticity, coherence light and so on. So laser have been widely used in many aspects, such as industrial laser cutting, processing, scanning, laser radar, laser interferometer, or medical application in surgery, hemostasis, removal of stains and correction of vision are important and indispensable tools for improving the quality of life of human beings. In addition, the monochromaticity of lasers and extremely short pulse waves have also become useful tools for discovering new properties of matter. Contributions in physics, chemistry, biomedicine, etc. can be described as increasingly important, so the development of new laser technology is also a major and eternal challenge. The traditional laser requires a two-sided reflector to form a resonant cavity, so that the gain medium accumulates enough photons in the resonant cavity, and laser light output when it reached the population inversion. Therefore, it is usually bulky, difficult to manufacture and costly. Conversely, for a random laser, it is important to generate a random factor in the laser light scattering. A randomly arranged scattering medium is used to form a closed scattering path similar to a resonant cavity, and excitation light generates multiple scattering through these closed loops. Once equilibrated the net gain of the system and the total losses, random laser emission canbe observed in several directions. Random lasers are simple, low cost, and small, making them suitable for many applications. Things like remote sensors, laser imaging, medical inspections, wearable sensors, displays or lighting, and more. In addition, we have also developed vertical cavity surface emitting lasers, which are widely used in optoelectronic technology and industry due to their surface normal emission, flexible packaging capabilities, and good beam quality. In addition, the tunability of spectral emission and laser mode selectivity can be achieved by designing the energy gap of the optical gain material and the resonance frequency in the surface-emitting laser cavity. Vertical cavity surface emitting lasers are a unique light source that can provide a wide range of applications, such as 3D sensing, high-speed data communications, and laser displays. This paper categorizes abstracts according to different research topics and methods of use in each chapter. The classification is as follows: 1. A Curvature-Tunable Random Laser The application of random lasers has been restricted due to the absence of a well-defined resonant cavity, as the lasing action mainly depends on multiple light scattering induced by intrinsic disorders of the laser medium to establish the required optical feedback that hence increases the difficulty to efficiently tune and modulate random lasing emissions. This study investigated whether the transport mean free path of emitted photons within disordered scatterers composed of ZnO nanowires is tunable by a curvature bending applied to the flexible polyethylene terephthalate (PET) substrate underneath, thereby creating a unique light source that can be operated above and below the lasing threshold for desirable spectral emissions. For the first time, the developed curvature-tunable random laser is implemented for in vivo biological imaging with much lower speckle noise compared to the non-lasing situation through simple mechanical bending, which is of great potential for studying fast-moving physiological phenomenon such as blood flow patterns in a mouse ear skin. It is expected that the experimental demonstration of the curvature-tunable random laser can provide a new route to develop disorder-based optoelectronic devices. The research results of this paper have been submitted to Nanoscale (10.1039 / c8nr09153f). 2. A Strain-Gauge Random Laser We describe a random laser that uses the ZnO nanorods (NRs) randomly orientated on a flexible polyimide (PI) substrate as disorderedly optical scatterers to stimulate coherent random lasing actions. Repeatable and reversible tuning of spectral emission is demonstrated by exerting a bending strain on the PI substrate, which enables us to activate the random laser on either below or above the lasing threshold. Furthermore, our random laser functions as a stable and durable optical strain gauge with a gauge factor of ≈37.7 5.4 under a bending strain of 40%, which is comparable to that of traditional electrical strain gauges. The study validates that the reported strain-gauge random laser is able to be used in certain fields where the electrical gauge is restricted and the optical gauge is considered to preferable as an alternative solution. The research results of this paper have been submitted to APL Materials (10.1063 / 1.5099316). 3. Graphene Quantum Dot Vertical Cavity Surface Emitting Lasers Nonzero-bandgap graphene quantum dots (GQDs) are novel optical gain materials promising for solution-processed light sources with high cost efficiency and device performance. Herein, we demonstrate for the first time room-temperature lasing emission with green gamut from GQDs in a vertical optical cavity composed of Ta2O5/SiO2 dielectric distributed Bragg reflectors (DBRs). The lasing is enabled by the unique design of the DBR which not only provides a wide stopband spectrally overlapping with the emission of the GQDs but also allows high transmittance of optical excitation in the UV-light region. This demonstration is a clear evidence of the use of GQDs as optical gain materials and represents an important step forward toward their potential applications in wide-gamut laser displays and projectors. The research results of this paper have been submitted to ACS photonics (10.1021 / acsphotonics.9b00976).
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Keywords
隨機雷射, 閥值可調式, 應變感測器, 石墨烯量子點, 垂直共振腔面射型雷射, Random Laser, Tunable Threshold, Strain Sensor, Graphene Quantum Dot, Vertical Cavity Surface Emitting Laser