Control of molecular ultracold plasma relaxation dynamics by mm-wave Rydberg–Rydberg transitions
Resonant mm-wave fields drive transitions in a state-selected Rydberg gas of NO. This transformation produces a clear signature in the selected field ionisation spectrum and dramatically increases the intensity of corresponding features in the spectrum of the Rydberg series observed in UV–UV double resonant transitions via the state. Here, refers to the principal quantum number of an f Rydberg state converging to the rotational state of NO. Enhancement owing to transitions from (f) to (g) appears both in the electron signal detected at early time by the field ionisation of Rydberg molecules and, later, as the late-peak signal of plasma in a state of arrested relaxation. Similar stabilisation and enhanced intensity also occurs for shorter-lived interloping complex resonances, and . We conclude from these observations that avalanche alone does not guarantee a plasma state of arrested relaxation. But rather, the formation of an arrested phase requires both avalanche-produced NO ions and a persistent population of long-lived Rydberg molecules. GRAPHICAL ABSTRACT