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Single particle extinction and scattering
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<p>Single Particle Extinction and Scattering (SPES) is a technique in <a href="/facts/Physics/a7aH2y08">physics</a> that is used to characterise micro and <a href="/facts/Nanoparticle/k8kNxX4E">nanoparticles</a> suspended in a fluid through two independent parameters, the diameter and the <a href="/facts/Refractive_index/yjkzvgeE">effective refractive index</a>. </p><p>A <a href="/facts/Laser/jk6PTvvT">laser</a> generates a <a href="/facts/Gaussian_beam/Hvo1wL29">gaussian beam</a> which focuses inside a flow cell. A particle that passes through the focal region generates an interference in the beam, which is collected with a sensor. Through this signal it is possible to derive the real part and the imaginary part of the forward scattering field from each particle. </p><p>The technique was developed to measure aerosols in air and particles in liquid. </p>