The Nitric Oxide Ultracold Neutral Plasma Produced By Laser Ionization Technology

Ultracold neutral plasma (UCP) is a novel research area as laser cooling mechanism appeared. Temperatures of electrons and ions of UCP are less than10K and1000K respectively. UCP can provide a possible route to approach the strongly-coupled regime under laboratory condition. Normally, the lifetime of ultracold plasma is very limited due to plasma heating and expansion mechanisms. In this paper, we mainly contribute to the UCP research from the following two aspects:(1) Nitric oxide (NO) was cooled to1K in a seeded Ar supersonic molecular beam. NO molecules were ionized by one-colour two-photon resonant enhanced multiphoton ionization (REMPI) process and formed ultracold plasma. The density of the ionized molecules in the illuminated volume approached to1.5x1013cm-3. Prompt electrons, plasma electrons and intact NO+ions were produced during this process. Experimental results confirmed the lifetime of this ultracold plasma was longer than18.3μs. This was the first report of NO ultracold plasma with significant lifetime being produced by one-colour two-photon REMPI process.(2) Then the laser radiate region was changed to20mm downstream general valve, and generated long lifetime ultracold plasma mainly consist of cations and anions. This plasma demonstrated characters of traversing a DC barrier of up to5(or-3) V. The lifetime of this plasma was expected more than250μs. Finally molecular dynamics (MD) simulation was used to explain how anions slow the expansion rate and prolong the lifetime of this plasma.