Simultaneous Tracking And Sizing Of Bubbles Under Ultrafast Illumination Based On Transient Scattering Statistics

Turbid and turbulent conditions arising from high-void-fraction bubbly flows remain experimentally challenging. Occlusion and photon scattering result in information loss, which, when compounded, becomes too significant for conventional approaches to mitigate. To remove the influence of scattered photons, ultrafast optical Kerr effect gating is implemented to selectively remove damaging scattered photons. As the separation of transient scattering modes is a function of bubble size, analysis of the gated ballistic light is also used to determine size. A new modified Optical Kerr Gate is introduced using a solid state wide-band gap semiconductor, producing Gaussian Kerr response with a FWHM of 414 fs. Two experimental frameworks within a vertical bubble column facility are introduced to simultaneously track bubbles and determine their sizes using minimal spatial information and a modified particle-tracking code. At low void fractions, this proved consistent with independent calibration and previous experimental studies. In higher void fraction conditions, tracking ballistic signals appeared successful for resolving velocities, even where physical occlusion became significant. Internal ballistic scattering modes were recovered, providing a basis to obtain bubble size distributions within optically thick conditions with continued development.