Coupling of Noncrossing Wave Modes in a Two-Dimensional Plasma Crystal

Abstract

We report an experimental observation of coupling of the transverse vertical and longitudinal in-plane dust-lattice wave modes in a two-dimensional complex plasma crystal in the absence of mode crossing. A new large diameter rf plasma chamber was used to suspend the plasma crystal. The observations are confirmed with molecular-dynamics simulations. The coupling manifests itself in traces of the transverse vertical mode appearing in the measured longitudinal spectra and vice versa. We calculate the expected ratio of the trace to the principal mode with a theoretical analysis of the modes in a crystal with finite temperature and find good agreement with the experiment and simulations.

Mode-coupling instability in a single-layer complex plasma crystal: Strong damping regime

“…Coupled longitudinal in-plane (L) and transverse outof-plane (TV) waves naturally excited and sustained in a 2D plasma crystal can be described by the following equations 29 :¨…”

“…These accelerations define the amplitudes of the naturally excited waves 29 . Ω L,V are the eigenfrequencies of the L and TV modes, whereas Ω W is the wake coupling frequency; their functional dependencies on the screening parameter κ and the wave number k are given below, see Eq.…”

“…is a coupling parameter, a convenient measure of the mixed mode polarization 29 . For p = 0, the L and TV modes are decoupled, the power of the mode coupling and mixed polarization increases rapidly with p for 0 < p < 1, while for p = 1 the hybrid mode appears.…”

“…Generally, the parameters Ω L,V,W are quite complicated functions of the wave propagation direction and wave number 3,4,29 . For our purpose, a rather simple nullδ model 4 will work well.…”

Full melting of a two-dimensional complex plasma crystal triggered by localized pulsed laser heating

“…Under certain conditions, this can lead to the formation of an unstable hybrid mode and the melting of the crystalline monolayer when the out-of-plane mode crosses the in-plane compressional mode: the mode coupling instability (MCI) [28][29][30][31][32]. The hybrid mode has clear fingerprints: critical angular dependence, a mixed polarization [33], distinct thresholds [30], and synchronization of the particle motion [34].…”