An assembly and a method for measuring the size of droplets or solid particles suspended in turbid media: polarization ratio imaging after multiple scattering suppression

An assembly for measuring size of particles, droplets or bubbles in a dense fluid, the assembly comprising:

• a linearly polarized light source;
• a polarization adjustment element for rotating the polarization of the linearly polarized light to an adjusted polarization angle;
• a spatial modulation element arranged to spatially modulate the linearly polarized light into a structured and polarized light profile;
• sheet generating means to create a structured and polarized light sheet from the structured and polarized light profile;
• a camera objective arranged to collect side scattered light from particles or droplets illuminated with the structured and polarized light sheet;
• a first 2D sensor arranged to detect a first image of the collected side scattered light of a first polarization direction;
• a second 2D sensor arranged to detect a second image of the collected side scattered light of a second polarization direction different from the first polarization direction;
• a processing unit arranged to
• calculate a first suppressed image and a second suppressed image by suppressing from the first image and the second image, respectively, a light intensity from multiple light scattering;
• calculate a polarization ratio image by calculating the ratio of the first suppressed image and the second suppressed image;
• and
• calculate a relative statistical diameter image based on the polarization ratio image;
• wherein the processing unit is further configured to calculate an absolute statistical diameter image based on the polarization ratio image and a calibration table of polarization ratio to particle or droplet diameter.