Ok,
http://www.startools.org/download/airy_refractor.tiff
Load this image into PhotoShop (it's important that your program supports 16-bit bit-depth).
You'll see a small star in the middle. This is a computer generated star, with an Airy Disk-like PSF applied.
Now launch a curve manipulation tool and start adjusting the white point down, way down.
Now you'll see how the star grows along the airy disk diffraction pattern as its core gets overexposed (multiplied).
Does this help?