ctemincohmtf.m

扫描电镜（stem）的matlab模拟程序代码

function mtf = ctemincohmtf(k,params,type)
%
%  MATLAB function to calculate CTEM bright field
%  contrast transfer function with partial coherence
%  for weak phase objects
%
%  function mtf = ctemincohmtf(k,params,type)
%
%    input array k has the spatial frequency values (in 1/A)
%    input array params has the optical parameters
%          params = [Cs, df, kev, ddf, beta]
%    input type = 0 for phase contrast
%           and 1 for amplitude contrast
%    output array contains the transfer function vs k
%
%  params ={ Cs, df, kev, ddf, beta, amax}
%  params.Cs   = spherical aberration (in mm)
%  params.df   = defcocus (in Angstroms)
%  params.kev  = electron energy (in keV)
%  params.ddf  = chromatic aberation defocus spread (in Angstroms)
%  params.beta = spread in illumination angles (in mrad)
%
%  rewritten and corrected 5-Jun-2006 Huolin Xin

Cs = params.Cs*1.0e7;
df = params.df;
kev = params.kev;
ddf = params.ddf;
beta = params.beta*0.001;

%calculated of electron wave legnth
%mo = 511.0;      % electron rest mass in keV
%hc = 12.3986;    % in keV-Angstroms
%wav = (2*mo)+kev;
%wav = hc/sqrt(wav*kev);

wav = 12.3986/sqrt((2*511.0+kev)*kev);  %electron wave length

K = (Cs*wav^3)^0.25.*k;                 %dimensionless k
Ks = (Cs*wav^3)^0.25*beta/wav;          %dimensionless k straggle
D = df/sqrt(Cs*wav);                    %dimensionless defocus
Ds = ddf/sqrt(Cs*wav);                  %dimensionless defocus straggle
E = pi^2*Ks^2*Ds^2;                     %dimensionless epsilon

K2 = K.*K;                              %K^2
base = 1+E.*K2;                         %1+E*K^2
prefactor = 1./sqrt(base);              %1/(1+E*K^2)^(1/2)

wr = pi.*K2./base.*(0.5.*K2.*(1-E.*K2)-D);
wi = prefactor.*exp(-(pi^2*Ks^2.*(K2-D).^2.*K2+0.25*pi^2.*Ds^2.*K2.^2)./base);

if type == 0
    mtf = sin(wr).*wi;
else
    mtf = cos(wr).*wi;
end;