體積全像於太陽能集光元件之應用研究

Abstract

本論文研究方向為體積全像集光元件之設計與實驗。採用全像材料PQ/PMMA作為體積全像記錄材料，並量測材料的吸收光譜，依吸收光譜決定使用吸收較大的綠光波長514.5 nm作為記錄光源，以及使用吸收係數較小的波長632.8 nm與594.1 nm作為讀取光源。在體積全像集光元件的光學實驗分成兩個部分進行，一為量測材料的光學特性，在此使用兩道光干涉之光學系統，記錄光柵於全像材料之中，並改變參數如樣品厚度與曝光能量，量測即時性與暗反應的繞射效率與各參數之關係性，在樣品厚度為3 mm的量測結果，曝光能量為2.0焦耳每平方公分時的繞射效率由42.11%提升至69.05%，具有較佳的暗反應效果以及繞射效率，因此我們選擇使用樣品厚度為3 mm進行90度光轉折實驗；另一為90度光轉折的實驗，以90度全像記錄系統來記錄光柵後再使用不同的光源重建，其繞射光將被轉折90度，在小樣品的實驗中曝光能量為2.25焦耳每平方公分時的繞射效率由39.94%提升至68.10%，而在大樣品的實驗中提供調制光強度分佈的方法，改善曝光能量對比度不均勻的問題，初步展示全像集光元件的概念。

In this thesis, a volume holographic concentrator is designed and tested for the first time. A PQ/PMMA material was chosen to record the hologram and it absorption property characterized by an integrating sphere. From this study, a wavelength 514.5 nm laser light is chosen as the recording beam and wavelength 632.8 nm and 594.1 nm laser light as the reading beams. Subsequently, we performed two optical experiments to realize the holographic concentrator. The first is to use two-beam interference experiment incident at ±45-degree to record grating in PQ/PMMA and to study its diffraction efficiency. This study allows us to determine optimum parameters, such as exposure energy, dark enhancement effect and sample thickness, for achieving maximum diffraction efficiency. It is found the use of 3 mm thick sample and 2 Joule per centimeter squared exposure-energy will lead to an efficiency of 69%. These parameters are then used to perform the second experiment, namely, 90-degree light bending experiment. In this experiment, two recording beams are incident from the top and the side surface of the sample. For reconstruction, the top-incident beam is diffracted by 90-degree and exit at the side-surface. Indeed, it is observed for the first time, that light can be bended by 90-dergee with high efficiency of 68% using our volume holographic approach. It is noted that, due to a strong attenuation of the recording beam in PQ/PMMA at wavelength 514.5 nm, there is an intensity-gradient along the side incident beam path. This gradient will change the relative beam intensities of the two recording beams, and affects diffraction efficiency. A method for overcoming this experimental constrain will be discussed in this thesis.