Bifurcation of Ultra-Cold molecular plasma in a supersonic molecular beam

Hossein Sadeghi, Markus Schulz-Weiling, Edward Grant
Departments of Chemistry and Physics, University of British Columbia

Molecular ultra-cold plasmas offer a pathway into the strong coupling regime under well-characterized and controlled laboratory conditions. Here we describe systems realized in supersonic beams. A supersonic beam offers the versatility of studying molecular systems and appears to yield stronger coupling. As a result of disorder-induced heating, ultracold neutral plasmas, created by photoionization to form with moderate correlation, generally exhibit a temperature rise that reduces coupling strength to a value less than one. Our experiment starts with a state-selected Rydberg gas, prepared by exciting nitric oxide molecules in a supersonic beam. Penning ionization with dissociation initiates an electron-impact avalanche that, for certain initial principal quantum numbers, forms a plasma with an ordered ion distribution. This plasma maintains a state of ion-ion correlation which has an observable effect on the rate of plasma expansion. Recently, by means of an imaging system we have discovered an interesting phenomenon manifested in directions orthogonal to the MCP detector. For certain densities and selected initial principal quantum numbers, the plasma bifurcates to form two lobes that exhibit arrested relaxation.