Beam quality of a non-ideal atom laser

TL;DR

This paper analyzes how a non-ideal atom laser's beam quality is affected by lensing effects from the Bose-Einstein Condensate, providing analytical descriptions and measuring the beam quality factor under various conditions.

Contribution

It introduces an analytical framework using WKB, Fresnel-Kirchhoff, and ABCD matrices to describe atom laser propagation and defines a generalized M$^2$ factor for beam quality assessment.

Findings

The atom laser exhibits caustics that depend on BEC density.

The analytical model accurately describes the propagation and caustic structures.

The measured M$^2$ factor varies with lensing effects, indicating changes in beam quality.

Abstract

We study the propagation of a non-interacting atom laser distorted by the strong lensing effect of the Bose-Einstein Condensate (BEC) from which it is outcoupled. We observe a transverse structure containing caustics that vary with the density within the residing BEC. Using WKB approximation, Fresnel-Kirchhoff integral formalism and ABCD matrices, we are able to describe analytically the atom laser propagation. This allows us to characterize the quality of the non-ideal atom laser beam by a generalized M$^2$ factor defined in analogy to photon lasers. Finally we measure this quality factor for different lensing effects.