Analyzing the measurement principle of laser particle size analyzer

Principle of laser particle size analyzer measurement

A laser beam emitted by a laser, after filtering, beam expansion, and calibration, becomes a parallel beam of light. In the case where the parallel beam does not irradiate the particles, the beam passes through a Fourier lens and converges on the focal plane to form a very small and bright spot - the focal point.

When particles are uniformly placed into a parallel beam in a specific way, the laser will undergo scattering, with a portion of the light diffusing outward at a certain angle to the optical axis. Both theory and practice have proven that the scattering angle of scattered light caused by large particles is small, and the smaller the particle, the larger the scattering angle of scattered light. These scattered lights from different angles will form a series of halos on the focal plane after passing through the Fourier lens, and the alternating light and dark spots composed of these halos are called Airy spots. Airy contains rich granularity information, which can be simply understood as halos with larger radii corresponding to smaller particle sizes, and halos with smaller radii corresponding to larger particle sizes; The light energy size of halos at different radii contains information about the content of particles of that size. In this way, we install a series of light receivers on the focal plane, convert the light signals scattered by particles of different sizes into electrical signals, and transmit them to the computer. Then, we use Mie scattering theory to mathematically process these signals through the computer to obtain the particle size distribution.