Collisional excitation transfer between Rb(5P) states in 50–3000 Torr of⁴He

Abstract

Measurements of the mixing rates and cross sections for collisional excitation transfer between the 5P1/2 and 5P3/2 states of rubidium (Rb) in the presence of 4He buffer gas are presented. Selected pulses from a high repetition rate, mode-locked femtosecond laser are used to excite either Rb state with the fluorescence due to collisional excitation transfer observed by time-correlated single-photon counting. The time dependence of this fluorescence is fitted to the solution of rate equations which include the mixing rate, atomic lifetimes and any quenching processes. The variation in the mixing rate over a large range of buffer gas densities allows the determination of both the binary collisional transfer cross section and a three-body collisional transfer rate. We do not observe any collisional quenching effects at 4He pressures up to 6 atm and discuss in detail other systematic effects considered in the experiment.

Kennard-Stepanov Relation Connecting Absorption and Emission Spectra in an Atomic Gas

“…Further, note that the thermalization within the excited state manifold also requires a redistribution between the rubidium fine structure components. In earlier work, the role of three-body collisions for fine structure changing collisions has been pointed out [15], which be-comes increasingly important for the much larger buffer gas pressures used in the present work.…”

“…A general description of absorption and emission probabilities requires a knowledge of the quasimolecular potential curves of the collision partners, a regime also known as collisionally aided excitation [13]. It furthermore has been noted that frequent atomic collisions can under suitable conditions lead to a thermalization of quasimolecular states [14,15].…”

Rubidium spectroscopy at high-pressure buffer gas conditions: detailed balance in the optical interaction of an absorber coupled to a reservoir

“…The Kennard-Stepanov scaling between absorption and emission is also of high relevance for recent experiments on the thermalization of photon gases in dye microcavity photon Bose-Einstein condensates [11,12,13]. Related, but in the non-equilibrium regime, the Kennard-Stepanov scaling is relevant for the operation of alkali-vapor lasers, which also build upon buffer gas broadened alkali atom filled gas cells [14]. High-pressure buffer gas alkali cells with comparable experimental parameters as the ones used in the present work have also been used in other work of our group for the demonstration of collisional redistribution laser cooling, which has achieved relative cooling of "macroscopic" gas samples by optical irradiation [15].…”

Transversely diode-pumped alkali metal vapour laser

“…In formulas (23) and (24) in accordance with the first condition in (12) we must assume , ( ) a q 1 3…”

“…In calculating collision frequencies v 31 and v 21 we assumed that s 31(CH 4 ) = s 21(CH 4 ) = 1.9 ´ 10 -18 cm 2 . For rubidium atoms in helium, collisional quenching cross sections are extremely small [s 31(He) , s 21(He) G 3 ´ 10 -20 cm 2 [24]), and thus quenching due to interaction with helium can be neglected.…”