Near-critical-angle scattering for the characterization of clouds of bubbles: particular effects

Abstract

We report experimental investigations on the influence of various optical effects on the far-field scattering pattern produced by a cloud of optical bubbles near the critical scattering angle. Among the effects considered, there is the change of the relative refractive index of the bubbles (gas bubbles or some liquid-liquid droplets), the influence of intensity gradients induced by the laser beam intensity profile and by the spatial filtering of the collection optics, the coherent and multiple scattering effects occurring for densely packed bubbles, and the tilt angle of spheroidal optical bubbles. The results obtained herein are thought to be fundamental for the development of future works to model these effects and for the extension of the range of applicability of an inverse technique (referenced herein as the critical angle refractometry and sizing technique), which is used to determine the size distribution and composition of bubbly flows.

Experimental validation of the vectorial complex ray model on the inter-caustics scattering of oblate droplets

“…1). This detection system is almost identical to the one developed for the study of critical scattering [17]. It is composed of a collection optics that image the droplet in the plane of an iris diaphragm and an achromatic doublet that performs the Fourier transform of the previously spatially filtered signal onto the chip of a high resolution CCD camera (4 Mpix, 14 bits).…”

Capillary-scale interferometry at high angles of scattering for refractive index measurements of small volumes

“…Although the analysis has been focused on the case of an analyte with the RI being equal to or greater than the RI of the capillary wall, rainbow formation is not limited to such a refractive profile. Also worth mentioning is that, when the analyte is of lower refractive index than capillary, the critical scattering angle technique may be applied for RI measurement, see works by Onofri and co-workers on scattering by water bubbles [36][37][38].…”

“…They manifest themselves in form of extremely narrow light pulses of the scattering intensity at resonance and do not usually appear in experiments with complex multi-phase systems (sprays, bubble clouds, etc.) [36][37][38][39][40][41]. Figure 4 shows a sketch of ray trajectories prepared for a capillary with the ID/OD = 0.1, supplemented with the rays of light that cause surface waves.…”

Inversion of Remote Sensing Data Using Multiple Ratios of Spectral Radiation Intensities and Neural Networks

“…In addition, one can analyse the impact of changes in various physical parameters on the radiation spectrum, that is to perform sensitivity studies. The impact of individual model parameters are studied in various types of inverse problems [19][20][21]. Quantitative interpretation of the measured spectrum usually consists of solving the inverse problem in relation to the problem of the calculation of the radiation spectrum, based on the knowledge of the gas contents and the temperature profile along the line of sight.…”