def METHOD_NAME(self, wavelength):
    '''Get the phase screen in radians at a certain wavelength.
    Parameters
    ----------
    wavelength : scalar
        The wavelength at which to calculate the phase screen.
    '''
    wavenumber = 2 * np.pi / wavelength
    opd = (self.refractive_index - 1) * self.surface
    return opd * wavenumber