docs: def reflection(n1, n2):
      '''
      Calculate the power reflection at the interface
      of two refractive index materials.
  
      Args:
          n1 (float): Refractive index of material 1.
          n2 (float): Refractive index of material 2.
  
      Returns:
          float: The percentage of reflected power.
      '''
      r = abs((n1-n2) / (n1+n2))**2
      return r