Spatiotemporal laser perturbation of competing ionization waves in a neon glow discharge

The experimental verification of spatiotemporal periodic pulling, a specifi c but universal phenomenon associated with driven, nonlinear, spatiotempora l systems, is reported as part of a study characterizing the ability of de and chopped laser light to induce periodic pulling in ionization waves prop agating in a neon glow-discharge plasma. The degree to which a single-mode laser beam at a metastable transition of 6401 Angstrom (1s(5)-2p(9)) influe nces the discharge is found to depend on the location and magnitude of the perturbation. Cases of ac (chopping the light) and de perturbation are pres ented. In a range of chopping frequencies above and below the ionization wa ve's undriven frequency, the wave can become synchronized to the perturbati on. This entrainment range is shown to depend on the frequency difference b etween the wave and the perturbation, as well as on the perturbation distan ce from the cathode. Hysteresis is found in the Value of the perturbation f requency associated with transitions into and out of entrainment. Outside o f entrainment, periodic pulling of a self-excited, propagating, ionization wave by the laser perturbation is observed. This is a case of frequency pul ling, or temporal periodic pulling. Inside of entrainment, the chopped lase r light controls the frequency and amplitude of the mode. By properly adjus ting the frequency and amplitude of one mode with respect to a second mode, periodic pulling of one ionization wave by the mode-locked, propagating, o riginal ionization wave is demonstrated. This is a case of spatiotemporal p ulling, involving both wavelength pulling and frequency pulling. Under prop er conditions, competition between temporal and spatiotemporal periodic pul ling results in a modulation in the dynamics of the system, a process refer red to as dynamics modulation.