the low-order harmonics disappear beyond the third one. Together, these simulations set boundaries on acceptable values of r 0 : the largest value (r 0 = 18.500 bohr) fails to attenuate the harmonics at the expected cutoff while the smallest value (r 0 = 4.000 bohr) attenuates the signal so much that nearly all of the harmonics are swallowed by the absorbing potential. Finally, Fig. uses r 0 = 9.524 bohr (as in Fig. ) but reduces the curvature η by a factor of 10. This choice restores the harmonic cutoff around 30th order but the spectrum exhibits spurious peaks above the 60th harmonic order, and these are somewhat stronger than they were for the larger value of η with the same turn-on radius.