(color online) Harmonic spectra of He atom (solid line) in a spatially inhomogeneous field with different inhomogeneous parameters: (a) β = 0, (b) β = 0.005, (c) β = 0.0055, (d) β = 0.0065. The harmonic energy excludes the ionization energy. The circles represent the dependence of the kinetic energy on the recombination time for the first rescattering. The red arrow and dash line show the cutoff position in the harmonic spectrum and the maximum returning energy from the first rescattering, respectively.