We investigate the use of Abbe-type refractometers with homogeneous absorbing fluids. We derive a simple model based on electromagnetic optics to describe quantitatively the angular distribution of light around the critical angle and report some experimental tests. First, we verify experimentally that the diffusing film near the base of the prism does in fact deliver light that refracts up to the critical angle. Then we compare experimental profiles of refracted light around the critical angle with theoretical profiles, and find very good agreement. Finally, we use the model to analyze some requirements and limitations on using Abbe-type refractometers on absorbing fluids.

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Identifying abnormalities in red blood cells can provide important medical clues for the diagnosis, prognosis, and treatment of some health disorders. A common test used to examine the conditions of erythrocytes in humans is osmotic fragility. The standard technique to determine the osmotic fragility of red blood cells is laborious and time-consuming, and provides only approximate values with a few experimental data. In this work, we propose and investigate a way to measure the osmotic fragility of erythrocytes, rapidly and in a straightforward, more quantitative and less laborious way, with an optical sensor. The basic idea is monitoring in real time the refractive index of a suspension of erythrocytes to follow the kinetics of their lysis as the hemoglobin-rich cytosol is released from the erythrocytes in the surrounding hypotonic solution during hemolysis, resulting in an increase of the refractive index. We propose a device to measure in real time the refractive index and demonstrate the feasibility of monitoring the hemolysis process with high resolution. Our results show that the release of hemoglobin-rich cytosol during the progress of the hemolysis of erythrocytes in hypotonic media is generally an exponential-like function of time. We provide a mathematical model that reproduces experimental curves effectively. We show results for erythrocytes obtained from human blood stored in a blood bank and from volunteers diagnosed with two different types of anemia: hemolytic and drepanocytic. We define times, measurable from the kinetics of the refractive index signal, to quantify the progress of hemolysis as a possible new method of measuring osmotic fragility.

We describe a method for obtaining the refractive index (RI), size, and concentration of nonabsorbing nanoparticles in suspension from relatively simple optical measurements. The method requires measuring the complex effective RI of two dilute suspensions of the particles in liquids of different refractive indices. We describe the theoretical basis of the proposed method and provide experimental results validating the procedure.

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