In ZEMAX, partially coherent transfer functions are characterized using a parametric function, Gamma. The Gamma function utilized for a particular Diffraction Image Analysis can be one of two types, Gaussian or Sinc (although others can be added upon request):

For the Gaussian Gamma function, the position vector, r, represents the distance between two points in the displayed image.

For both functions, the parameter α (Alpha) is a scaling parameter defined in lens units. This parameter sets the effective width of the Gamma function. The smaller that Alpha is, the narrower the resulting Gamma function. Narrow Gamma functions produce partially coherent images that are, for the most part, incoherent.

On the other hand, larger Alpha values produce comparatively broad Gamma functions. Broad Gamma functions generate partially coherent images that are very similar to coherent images.

Open the menu option, “Analysis > Image Analysis > Diffraction Image Analysis”. Change the following options:

• “File Size” to 0.1
• “Oversampling” to 14X
• “File” to BAR.IMA
• “Data Type” to Partially Coherent Test: Gamma
• “Alpha” to 0.0025
  

The resulting Gamma function for an Alpha value of 0.0025 is relatively narrow and will produce partially coherent images that are mostly incoherent:

Now, open the settings dialog and change “Alpha” to 0.1. Now that Alpha has been increased, the corresponding Gamma function is very broad and will produce partially coherent images that are mostly coherent: