old_contents: from LightPipes import *
  import matplotlib.pyplot as plt
  
  wavelength=5*um
  size=25.0*mm
  N=500
  
  F=Begin(size,wavelength,N)
  F=GaussHermite(0,0,1,size/3,F)
  F=CircScreen(3*mm,0*mm,0*mm,F)
  F=Fresnel(20*cm,F)
  I=Intensity(2,F)
  
  plt.imshow(I,cmap='jet'); plt.axis('off'); plt.title("Poisson's spot")
  plt.show()
  
new_contents: from LightPipes import *
  import matplotlib.pyplot as plt
  import numpy as nb
  wavelength=500*nm
  size=5*mm
  N=500
  r=nb.arange(-size/2,size/2,size/N)
  F=Begin(size,wavelength,N)
  F=GaussHermite(0,0,1,size/3,F)
  F=CircScreen(1*mm,0*mm,0*mm,F)
  F=Fresnel(40*cm,F)
  I=Intensity(1,F)
  plt.plot(r,I[250])
  #plt.imshow(I,cmap='jet'); plt.axis('off'); plt.title("Poisson's spot")
  plt.show()
  
subject: Update Poisson.py