South African Journal of Science
On-line version ISSN 1996-7489
The graded index (GRIN-like) medium generated by gas inside a heated steel pipe when rotated about its longitudinal axis has the ability to focus a laser beam. While the effective focal length of such a system has previously been studied, there is little information on optical phase aberrations and no study to date on the propagation parameters of the laser beam, but has rather remained rooted in the domain of ray optics. We revisit the spinning pipe gas lens in this paper with new perspectives on the propagation of optical waves, and show how the position of the focus is not a measure of the focal length of the lens. We make use of both the intensity and phase information carried by waves to accurately measure the salient parameters of the lens, and complement our experimental findings with a computational fluid dynamics model.