Absolute-frequency measurement of the narrow-linewidth 24-THz D–D transition of a Single laser-cooled barium ion

Abstract

A single 138Ba+ ion, trapped in a rf trap and cooled to 15 mK by 493- and 650-nm dye-laser radiation, was probed by 24-THz radiation from an optically pumped ammonia laser. The absorption lines corresponding to two Zeeman components of the 5d2D3/2–5d2D5/2 transition, symmetrically located about the line center, were scanned while the laser frequency was being simultaneously measured relative to a Cs primary frequency standard by the National Research Council phase-locked frequency chain. The frequencies of the Zeeman components were obtained, and the transition line center was determined to be 24012048319 ± 1 kHz.