[SA_scat] Small Angle Light Scattering - Data Analysis

[Michael Girard]

Dear All,

I am new to small angle scattering, and I have started to develop the  
technique of small angle light scattering (SALS) to analyze fiber  
orientations in engineered polymer films and thin biological tissues  
(such as the sclera - the white part of the eye). My knowledge of  
optics is quite limited and I would like to ask some advices regarding  
SALS data analysis. I hope this is the right place to ask this  
question, and If not please disregard this email.

 From this link:
http://homepage.mac.com/michael.girard/SALSfibers.jpg
A scattered pattern can be found that was obtained with my SALS  
apparatus (A HeNe laser beam passed through a polymer film with highly  
aligned fibers - On the left is a snapshot from a monochrome CCD  
camera).

I have wrote a small program to extract Intensity vs azimuthal angle  
information (the most precious information I am looking for). Briefly,  
image pixel intensity was recorded (from the red circle - the pixels  
that are actually closest to that circle and averaged in small windows  
for smoothing) and plotted as a function of the azimuthal angle (0 to  
360 degrees - Blue plot on the right).

The peaks of that curve give me the preferred fiber orientation of my  
material (shifted 90 degrees). However I have more concern about the  
spread of that "Gaussian-Like" distribution:

I am a bit confused about one thing:
If I change the radius of my red circle, my blue curve is changing  
(mainly the spread will change and the curve is translated  
vertically). This sounds a bit like a problem to me. I am looking for  
some criteria, based on optics theories, in order to obtain "real" and  
repeatable intensity plots.

Should I consider looking at the intensity vs scattering angle plots  
(i.e. Image intensity following radial directions from the center of  
the image)?

If anybody would have some advice regarding SALS data analysis, I  
would greatly appreciate. If you would prefer to redirect me toward a  
publication I would greatly appreciate as well.

Thanks much for your time,

Michael

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Michaël J. A. Girard, Ph.D.
Department of Bioengineering
Imperial College London
South Kensington Campus
London SW7 2AZ, UK
m.girard at imperial.ac.uk
+44 (0)7826 351 685
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