Single Particle Extinction and Scattering

EOS particle analysers are based on patented Single Particle Extinction and Scattering (SPES) method, a step forward in the way light scattering is exploited for single particle characterization of in fluids as complex liquids and aerosols. SPES and dedicated data analysis algorithms provide more reliable and meaningful information, boosting R&D – QC processes, during lab scale design and industrial production of particles. Added-value information is provided thanks to SPES and EOS Classizer™ unique data and analysis libraries:

  • Particle Optical Classification, Absolute Particle Size Distribution, Numerical Concentration of each single population irrespectively of polydispersity/composition.
  • Quality Control of particle porosity, wetting, aspect ratio, payload, impurities, scraps, and shelf-life without intermediate steps (purification/filtration).
  • Measurement of particle behavior and formulation stability directly in real heterogeneous non-filtered target biological, industrial, or environmental fluids.
  • Hi-Resolution Continuous Flow Analysis, also coupling SPES information with other analytical devices as CF3 separators, small chemical reactors, and pilot line.
  • Statistical approaches as Oversize Measure and PCA for Hi-Quality Batch-2-Batch analysis and out-of-specifics identifications in product formulation and production.

How Does SPES Work in Brief?


The patented Single Particle Extinction and Scattering method is based on a self-reference interferometric measurement of the scattered wavefront in the forward direction by a single illuminated particle. Particles are driven by a laminar fluid flow (liquid or gas depending on the application/Classizer™ version) through the waist region of a tightly focused laser beam.


The intense transmitted beam interferes with the faint scattered wavefront in the far field, thus superimposing the two waves with the same curvature. This causes the interference pattern to exhibit intensity modulations on the spatial scale of the beam itself. Two scattering features are sampled to follow the evolution of the interference fringes during the passage of a particle through the beam: i) a global beam attenuation given by the extinction cross section of the particle, removing a small fraction of the incoming power; ii) the fringes given by the partial constructive and destructive interference, proportional to the amplitude of the forward a-dimensional scattered field S(0). These features are directly related to the real Re S(0) and the imaginary Im S(0) components of  complex field S(0), as stems from the Optical Theorem [H. C. van de Hulst, Light Scattering by Small Particles, 1981].


Im S(0) and Re S(0) are retrieved for each single detected and counted particle thanks to a robust Pulse Shape validation scheme, without adopting ill-posed problems like the inversion or deconvolution (note: other optical parameters could be alternatively retrieved instead of S(0) components, as particle extinction cross section Cext, particle polarizability α, or particle optical thickness ρ). In a few minutes SPES creates the unique EOS CLOUDS: a 2D histogram which is the optical fingerprint of the sample. Heterogeneous samples produce simultaneously different clouds for each particle population, which can be individually selected, analysed, and compared.


SPES easily provides the Numerical Particle Size Distribution and other statistical values as AVG, CV, and quantiles thanks to EOS unique particle data libraries. Statistical approaches as PCA are furthermore possible for extracting valuable information typically inaccessible nowadays.

EOS boosts innovation through SPES! We provide standard solutions and Technology Transfer Services to revolutionize your products development, formulation and promote effective quality controls of micron sized and submicron particles in biological, industrial, and environmental heterogeneous fluids.