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FRAUNHOFER THEORY |
 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
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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.
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| MIE THEORY |
The Fraunhofer theory is applicable for large particles compared to the wavelength l (diffusion and absorption are not considered).
For smaller particles, it is appropriate to use Mie Theory.
The Mie model takes into account both diffraction and diffusion of the light around the particle in its medium.
To use the Mie model, it is necessary to know the complex refractive index of both the sample and the medium.
This complex index has a real part, which is the standard refractive index, and an imaginary part, which represents absorption.
Complex index = m
m = a + b
a : real part
b : imaginary part
Because of the importance of this model, CILAS has crated a fast algorithm, which enables the user to get, within seconds, diffusion results using Mie theory and taking into account the complex index of the sample. |
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What’s New |
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Come and see our solutions at the following trade shows :
(for more details, click on the shows).
USA
 International Conference & Exhibition on Advanced Ceramics & Composites
Booth 303
Daytona Beach, FL
January 20 - 21, 2009
TMS Annual Meeting
Booth 600
San Francisco, CA
February 16 - 18, 2009
Pittcon 2009
Booth 938
Chicago, IL
March 8 - 13, 2009
Particle Society of Minnesota
Roseville, MN
March 2009
Regional Refractories
St. Louis, MO
March 25 -26, 2009
Chicago Catalyst Show
Chicago, IL
May 12 - 14, 2009
National Catalyst Show
San Francisco, CA
May 14, 2009
Southeast Catalyst Show
Ashville, NC
June 7 - 12, 2009
MS&T 2009
Pittsburgh, PA
October 25 - 29, 2009
American Association of Pharmaceutical Scientists 2009
Los Angeles, CA
November 8 - 12, 2009 |
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