Hyperfine state-changing collisions ofCs(6P1∕2)atoms with argon perturbers

Abstract

A two-step excitation experiment has been employed to measure the collisional rate coefficients and to study the velocity distribution of Cs͑6P 1/2 ͒ atoms that have undergone a single hyperfine state-changing collision with Ar. In addition, argon pressure broadening rates and shifts of the cesium 6P 1/2 ͑FЈ͒ → 8S 1/2 ͑FЉ͒ transitions have been determined. In the experiment, a single mode, cw Ti:sapphire laser is tuned to line center of the 6S 1/2 ͑F =4͒ → 6P 1/2 ͑FЈ = 3 or 4͒ transition. Then, the frequency of a single mode cw dye laser is scanned over the 6P 1/2 → 8S 1/2 manifold to probe the populations of the 6P 1/2 hyperfine levels. Absorption of probe laser photons is monitored by detecting 8S 1/2 → 6P 3/2 fluorescence. The experiment is conducted at room temperature, where the Cs density is low ͑n ϳ 3.4ϫ 10 10 atoms cm −3 ͒, and thus the probability of a Cs-Cs collision is negligible during the Cs͑6P 1/2 ͒ radiative lifetime. The Ar pressure is varied from 0 to 1.52 Torr, and Cs-Ar collisions cause population to be transferred from the directly excited 6P 1/2 ͑FЈ͒ level to the other 6P 1/2 hyperfine level. The data are analyzed using a density matrix formalism to yield the rate coefficients for Cs͑6P 1/2 ͒-Ar hyperfine state-changing collisions. In addition, the one-dimensional velocity changing collision kernel for Cs͑6P 1/2 ͒ atoms prepared with v z = 0 that undergo FЈ =3↔ FЈ = 4 hyperfine state-changing collisions with argon is reported.

U.S. Resourcing to National Security Interests in Latin America and the Caribbean in the Context of Adversary Activities in the Region

“…Russian exports to global markets primarily consist of arms, energy, and metals, and LAC still represents a small fraction of their total exports. 275 Russia gains foreign currency from electricity infrastructure projects 276 and space services and sells limited amounts of vehicles and other goods to Cuba and a few other countries. 277 On the other side of the ledger, after sanctions prevented imports from traditional trading partners in Europe and the United States, Russia turned to LAC countries to boost food supplies, particularly from Argentina and Brazil.…”

“…Initially attributed to domestic actors, events in Venezuela later suggested some election meddling campaigns were accomplished with direct Russian assistance. 331 In January 2018, former U.S. national security adviser H. R. McMaster said that the United States had seen "a sophisticated effort to influence the ongoing Mexican presidential campaign." 332 Reportedly, Mexico's National Electoral Institute "concluded that 65 percent of the visits to Mexico's website for voters abroad came from computers located in St. Petersburg, Russia," and, later in 2018, Russian disinformation targeted a national election in Colombia in addition to around 50,000 cyberattacks on Colombia's national voter registry.…”

Velocity preserving transfer between highly excited atomic states: black body radiation and collisions

“…Nevertheless, the effects of collisions in redistributing or thermalizing the atomic velocities has remained so far unexplored for high-lying excited states for which radiation trapping and resonant exchange collisions with ground state atoms are expected to reduce. This could unmask collisional mechanisms that preserve a memory of the laser selected velocities, previously studied mainly with molecules [10] or buffer gas perturbers [11][12][13].…”