  We investigated the self-excited as well as optogalvanically stimulated
heartbeat instability in RF discharge complex plasma. Three video cameras
measured the motion of the microparticles, the plasma emission and the
laser-induced fluorescence simultaneously. Based on the experimental results we
suggest that the void contraction during the instability is caused by an abrupt
void transition from the dim to the bright regime [Pikalev et.al., accepted to
PSST (2021), DOI: 10.1088/1361-6595/abe0a2 ]. For the self-excited heartbeat
instability, this transition is induced by the growth of the breathing
oscillations of the microparticle suspension.
