George N, Jain A
Appl Opt. 1973 Jun 1;12(6):1202-12. doi: 10.1364/AO.12.001202.
The occurrence and smoothing of speckle are studied as a function of the line width for a highly collimated illuminating source. A general theory is presented for speckling in the image of a partially diffuse, phase type of object, which has a variable number of random scattering centers per resolution element. Then, an expression is derived for the wavelength spacing required to decouple the speckle patterns arising from two monochromatic tones in an imaging system, thereby establishing that it is feasible to smooth speckle using multicolor illumination. This theory is verified in a series of experiments using both laser illumination and band-limited light from a carbon arc. With highly collimated sources, we show that speckle appears laserlike for an imaged diffuser even up to line widths of 5 A. Then, smoothing of speckle is demonstrated in the imaging of a diffuser and for a section of an optic nerve when the illumination is provided by six narrow lines spread over 1500 A. Since with color-blind, panchromatic viewing the speckle smooths, a direct extension of this method to holographic microscopy, using a multitone laser, should permit one to record and reconstruct holograms of diffraction-limited resolution that are essentially speckle-free.
研究了对于高度准直的照明源，散斑的出现和平滑与线宽的函数关系。针对部分漫射、相位型物体的图像中的散斑现象，提出了一种通用理论，该物体每个分辨率元素具有可变数量的随机散射中心。然后，推导出了成像系统中使两个单色色调产生的散斑图案去耦所需的波长间距表达式，从而证明了使用多色照明平滑散斑是可行的。该理论在一系列实验中得到验证，这些实验使用了激光照明和来自碳弧的带限光。对于高度准直的光源，我们表明，即使线宽达到5埃，成像扩散器的散斑看起来也类似激光散斑。然后，当由分布在1500埃范围内的六条窄线提供照明时，在扩散器成像和视神经切片成像中展示了散斑的平滑效果。由于在色盲、全色观察下散斑会平滑，使用多频激光将此方法直接扩展到全息显微镜，应该能够记录和重建具有基本无散斑的衍射极限分辨率的全息图。
