Device and method for multiparameter measurements of microparticles in a fluid

A method of classifying and of flow measuring the refringence of at least two populations of particles present in a fluid by using a light source of short coherence time, of coherence length Lc<100 μm, used under extinction conditions at a center wavelength selected as a function of the range of volumes and the range of refractive indices expected for the particles under consideration, the method comprising the steps of:

• using the light source to form a converging illuminating beam of aperture angle lying in the range 1° to 60°, selected as a function of the range of volumes and the range of refractive indices expected for the particles under consideration at the selected center wavelength and presenting lighting uniformity better than 10% in a rectangular volume measuring a×b×c, where a×b is the rectangular section of the beam having an aspect ratio a/b of less than 4, and where c is the depth of field defined as being the range of distances about the measurement point for which the power varies by no more than 10%, its value being situated at about 500 μm±250 μm;
• causing the fluid with particles to flow through a measurement orifice;
• measuring impedance vibrations (RES) as the particles go through the measurement orifice;
• causing the fluid with particles to flow in the measurement window illuminated by the beam placed at the outlet from the measurement orifice;
• measuring extinctions (EXT) on the axis of the beam as the particles pass through the measurement window, the measurement being performed by means of a device or a detector having a converging reception beam of aperture angle lying in the range 1° to 60° selected as a function of the range of volumes and the range of refractive indices expected for the particles under consideration;
• merging the RES and EXT data to form events therefrom;
• evaluating a relative refractive index IDX for each event;
• and
• classifying all of the events using at least one parameter selected from RES, EXT, and IDX.