  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. Comprehensive studies of the
optogalvanic control of the heartbeat instability revealed that the
microparticle suspension can be stabilized by a continuous laser, whereas a
modulated laser beam induces the void contraction either transiently or
resonantly. The resonance occurred when the laser modulation frequency
coincided with the frequency of small breathing oscillations of the
microparticle suspension, which are known to be a prerequisite to the heartbeat
instability. 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., Plasma Sources Sci. Technol. 30,
035014 (2021)]. In the bright regime, a time-averaged electric field at the
void boundary heats the electrons causing bright plasma emission inside the
void. The dim void has much lower electric field at the boundary and exhibits
therefore no emission feature associated with it.
