Distribution characteristics of intensity and phase vortices of speckle fields produced by N-pinhole random screens
Liu Man†a),b), Cheng Chuan-Fu‡b), Ren Xiao-Rongb)
       
The local probability distributions of ∂φ / ∂θ . (a) N = 4, (b) N = 8, (c) N = 10, (d) N = 12, (e)  N = 16, (f)  N = 20, (g) a large single ring aperture and (h) a large single circular aperture.