Coherent Backscattering from Multiple Scattering Systems - KOPS ...

Evaluation of the wide angle data
Evaluation of the wide angle data
This MATLAB script calibrates and displays the data of the wide angle setup (secs. 3.2 and
5.1), calculates the integrated cooperon E, and draws a theory curve which can be fitted to the
data by varying the value for the transport mean free path l ∗ .
Each data set consists of a series of reference measurements at different incoming laser powers
and one measurement with the sample itself. The data are stored in ASCII files which contain
the diode signals and their errors. The diode positions (in degrees) are read from the file
‘diode angles.dat’. The filenames of the data files contain the average incoming laser powers
and their errors (in arbitrary units), which are measured by the power meter in the setup.
The albedo mismatch ℵ = A reference /A sample has to be calculated from eqn. 5.6, diffusion
coefficient D and absorption time τ are measured in time of flight experiments (sec. 3.4), and
the effective refractive index n eff is calculated using eqn. 4.1. With the variable ‘enhancement’
the height of the theoretical cone can be adapted to that of the measured one.
function wide_angle_evaluation
%% Initialize variables and load files
file_samp = ’C:\Examples\example_0.100+-0.001.dat’ ; % sample file
path_ref = ’C:\Examples\’ ;
% path reference files
name_ref = ’teflon_01_0.200+-0.001.dat’ ;
% arbitrary reference file
wavelength = 590e-9 ;
D = 15 ;
tau = 2e-9 ;
n_eff = 1.58 ;
l = 500e-9 ;
aleph = 0.890 ;
enhancement = 0.9 ;
% laser wavelength
% diffusion coefficient of the sample
% absorption time of the sample
% effective refractive index of the sample
% transport mean free path for theory fit
% albedo mismatch
% enhancement of the backscattering cone
% angular positions of the photodiodes
angles = load (’C:\Examples\diode_angles.dat’,’-ascii’) ;
theta = angles * pi / 180 ;
% sample file
data_samp = load (file_samp,’-ascii’) ;
parts = regexp (file_samp, ’_|+-|.dat’, ’split’) ;
P_samp = parts ( size(parts,2) - 2 ) ;
P_samp = str2double (P_samp:,1) ;
Perror_samp = parts ( size(parts,2) - 1 ) ;
Perror_samp = str2double (Perror_samp:,1) ;
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