Assumptions
Spherical, non-porous and opaque particles,
Diameter d > wavelength l,
Particles are distant enough from each other,
Random motion,
All the particles diffract the light with the same efficiency, regardless of.
Characteristic of the Airy shape
Circular,
Consisting in concentric rings I = f (a),
Spacing and size of the rings are linked to the particle size,
The fist zero angle is related to the diameter d by 1.22 l/d,
75% of the total energy is concentrated in the first lobe.
Principle
Aspect of the diffraction pattern with respect to the particle size
System
for a large particle |
System
for a small particle
|
The observation of the diffraction pattern at finite distance is done through a lens (L) placed between the laser source and the detector
The diffraction patterns of particles having the same size converge at the same point whatever them location with respect to the lens,
The first zero on the detector is 1.22 lf/d where f is the focal length.
Pittcon 2012