def reflection_normal(n1, n2):
    """
    Fresnel reflection losses for normal incidence.

    For normal incidence no difference between s and p polarisation.

    Inputs:
    n1 : Refractive index of medium 1 (input)
    n2 : Refractive index of medium 2 (output)

    Returns:
    R : The Fresnel

    Doctests:
    >>> '%.2f' % reflection_normal(1.5,1)
    '0.04'
    """
    return((n1-n2)/(n1+n2))**2.