- 學位論文
雷射光斑特性的量測與分析
Study of Measurement and Analysis of the Laser Speckle Characteristics
摘要
在同調光源的成像系統中，光斑（speckle）現象一直都是降低影像品質的重要因素之一，因此，降低光斑的影響是近來需要研究的課題。由於這原因，客觀的量測同調投影系統，其影像中的光斑現象，對於抑制光斑來講能夠有更正確的依據。主要用來評估光斑影響程度的參數，稱為光斑對比值（speckle contrast），此參數是利用截取到影像中光強的標準差跟其平均的比值而得。當我們在擷取影像，其量測系統中的各項參數不同時，例如入射光功率量測距離及量測角度等，皆可能造成光斑對比值有所差異。 論文之主要目的是當在不同的量測角度來擷取影像及不同入射光功率時，其所帶來之光斑對比的數值變化，且利用計算其光斑大小（speckle size）來驗證此光斑對比值的可信度。我們沿用先前研究的結果，因為任何強度不均勻的影像都能計算出其光斑對比值，但是無從判斷其發生的機制是近場亦或遠場繞射，惟有從影像中的光斑大小才能正確判別。本實驗架構之方法是將量測距離固定，截取不同的光強及量測角度之光斑圖，利用Matlab程式算出個別光斑對比值及其光斑大小。從實驗結果發現，量測角度變大時光斑對比值會隨之下降，而光強加大時光斑對比值也會隨之下降。
並列摘要
In the imaging system by using coherent light, speckle phenomenon has always been important to reduce quality of image. Therefore, reducing the impact of speckle is an important problem. In order to have more precise result for reduction speckle, measuring the coherent projection system objectively leads to a more correct basis. The parameters which is mainly used to evaluate effect of speckle are speckle contrast, this parameter is defined by image intensity standard deviation over intensity average. When we captured images, and measured the difference between parameters of the system, Ex. measuring distance and measurement angle, which will cause different speckle contrast. The main purpose of this thesis is different angle or intensity will cause the different speckle contrast, and calculate the speckle size to verify the credibility of speckle contrast value. We follow the results of previous studies. Due to any uniform image intensity can be calculated its speckle contrast. However, there is no way to determine its mechanism which is either near or far field diffraction. Only from the speckle size in image can correctly differentiate that. The frame of the experiment is keeping the measuring distance in constant. Capturing the image which have different light intensity and measuring angle, and using Matlab program to calculate the individual speckle contrast and its speckle size. From the experimental results, when the measurement angle increase, the speckle contrast will decrease. And when the intensity increase, the speckle contrast decrease.