In this work, a numerical modal decomposition approach is applied to model the optical field of laser light after propagating through a highly multi-mode fiber. The algorithm for the decomposition is based on the reconstruction of measured intensity profiles along the laser beam caustic with consideration of intermodal degrees of coherence derived from spectral analysis. To enhance the accuracy of the model, different approaches and strategies are applied and discussed. The presented decomposition into a set of LP modes enables both the wave-optical simulation of radiation transport by highly multi-mode fibers and, additionally, the analysis of free-space propagation with arbitrarily modified complex amplitude distributions.

In this paper we study the rise to the surface, radial motion and disappearance of the bubbles created by a water jet pouring into a container, in particular their density at the surface as a function of the impact velocity. We first focus on their emergence radius at the surface which follows a log-normal distribution. Next, we establish experimentally a law relating the bubble velocity to the distance to the jet. We also investigate their disappearance, caused at low density mainly by explosion, and at high density predominantly by coalescence. Finally, we build an accurate model for the density of bubbles.