docs: def electric_field_amplitude_intensity(s0, Isat=16.6889462814,
                                         Omega=1e6, units="ad-hoc"):
      """Return the amplitude of the electric field for saturation parameter.
  
      This is at a given saturation parameter s0=I/Isat, where I0 is by default \
  Isat=16.6889462814 m/m^2 is the saturation intensity of the D2 line of \
  rubidium for circularly polarized light. Optionally, a frequency scale \
  `Omega` can be provided.
  
      >>> print(electric_field_amplitude_intensity(1.0, units="ad-hoc"))
      9.0152984553
      >>> print(electric_field_amplitude_intensity(1.0, Omega=1.0, units="SI"))
      112.135917207
      >>> print(electric_field_amplitude_intensity(1.0, units="SI"))
      0.000112135917207
  
      """
      E0_sat = sqrt(2*mu0*c*Isat)/Omega
  
      if units == "ad-hoc":
          e0 = hbar/(e*a0)  # This is the electric field scale.
          E0_sat = E0_sat/e0
  
      return E0_sat*sqrt(s0)