Hydrodynamic behavior in expanding thermal clouds of Rb-87

TL;DR

This paper investigates the hydrodynamic expansion of Rb-87 thermal clouds, revealing anisotropic expansion and significant cooling effects, with an analytical model to describe these phenomena and implications for thermometry.

Contribution

It introduces an analytical model for the hydrodynamic expansion of Rb-87 clouds, highlighting cooling effects and anisotropic behavior at high densities.

Findings

Cloud temperature drops by up to 30% during expansion

Expansion is anisotropic at high densities

Analytical model effectively describes cooling and expansion

Abstract

We study hydrodynamic behavior in expanding thermal clouds of Rb-87 released from an elongated trap. At our highest densities the mean free path is smaller than the radial size of the cloud. After release the clouds expand anisotropically. The cloud temperature drops by as much as 30%. This is attributed to isentropic cooling during the early stages of the expansion. We present an analytical model to describe the expansion and to estimate the cooling. Important consequences for time-of-flight thermometry are discussed.