In this work, we used a simple accurate method to measure the short temporal coherence length of a light emitting diode. This method is based on accurate visibility determination of Newton’s ring fringes. The visibility of Newton’s rings has its maximum value around the position of contact point between the spherical and the plane surfaces while it decreases, until vanishing, with moving towards the outer rings. This is due to the gradually increasing thickness of the air gap separating the two surfaces; starting from zero at the contact point. When the lowest detectable value of visibility tends to zero, there are only two interfered rays which are temporarily separated by the value of the temporal coherence length of the used light source. By detecting these two rays and calculating their optical paths, it was easy to evaluate the temporal coherence length of the used light source. For the purpose of accuracy enhancement, both intensity and visibility calculations of each detected interference order were automatically determined by employing an algorithm prepared using MATLAB software environment. Moreover, tracing the real optical paths of the two interfered rays forming the interference enabled us to calculate the spatial distance which is separating them without any approximation. This distance was too short (<20 nm) which means that we almost dealt with a pure temporal coherency. In this work, three commercial light emitting diode sources with different wavelengths were investigated and their temporal coherence length values were determined. Investigation of tolerance of temporal coherence length measurement was discussed.

在这项工作中，我们使用了一种简单而精确的方法来测量发光二极管的短时间相干长度。该方法基于牛顿环条纹的准确可见性确定。牛顿环的能见度在球面与平面之间的接触点位置附近具有最大值，而随着向外环的移动，它的减小直到消失为止。这是由于分隔两个表面的气隙厚度逐渐增加所致。在接触点从零开始。当可见性的最低可检测值趋于零时，仅两条被干扰的射线被所使用的光源的时间相干长度的值暂时分开。通过检测这两条射线并计算它们的光路，评估所用光源的时间相干长度很容易。为了提高准确性，通过使用在MATLAB软件环境下准备的算法，可以自动确定每个检测到的干扰阶数的强度和可见度计算。此外，追踪形成干涉的两条受干扰光线的实际光路，使我们能够计算将它们分开的空间距离，而无需进行任何近似计算。该距离太短（<20 nm），这意味着我们几乎处理了纯粹的时间一致性。在这项工作中，研究了三种具有不同波长的商用发光二极管光源，并确定了它们的时间相干长度值。讨论了时间相干长度测量公差的研究。