def topHat(r,A0=0.2):
        """Top-hat beam profile as used in Ref. [1].
        
        Args:
            r (numpy array, ndim=1): Equispaced 1D grid for radial coordinate.
            A0 (float): Top hat width (default: 0.2).

        Returns: 
            f (numpy array, ndim=1): Top-hat beam profile.
        """
        return r<A0