Hexagonal superlattice state in dielectric barrier discharge

We report on the observation of a hexagonal superlattice state (HSS) in dielectric barrier discharge in air/argon near atmospheric pressure. It bifurcates directly from the hexagonal state by increasing the applied voltage. The correlation measurements indicate that the HSS is an interleaving of three different transient sublattices. The spatial power spectrum demonstrates that the HSS has two separate wave vectors. The big wave vector and the small wave vector belong to the harmonic mode and the subharmonic mode, respectively, and they obey the triad resonant interaction (q) over right arrow (s)(1)+(q) over right arrow (s)(2)=(K) over right arrow (h)(c).