def setup_fftw(self, pulse_in, fiber, output_power, raman_plots = False):
        ''' Call immediately before starting Propagate. This function does two
        things:\n
        1) it sets up byte aligned arrays for fftw\n
        2) it fftshifts betas, omegas, and the Raman response so that no further\n
            shifts are required during integration. This saves lots of time.'''