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%---------------------------------------------------------------
% Returns the q-factor of a Gaussian beam given the spot size,
% phasefront radius of curvature and wavelength.
%
% SYNTAX: qfactor=q_(w,R <,lambda>);
%
% w = 1/e Field radius
% R = Radius of curvature of phasefront
% lambda = wavelength
%
% Any one of w, R and lambda may be a vectors or scalars.
% If more than one of w, R and lambda is a vector, all
% vectors supplied must be the same size. w, R and lambda must
% all be in the same units.
%
%--------------------------------------------------------------
% SYNTAX: qfactor=q_(w,R <,lambda>);
%--------------------------------------------------------------
function qfactor=q_(w,R,varargin)
if nargin>=3, lambda=varargin{1}; else lambda=1064e-9; end
if R~=Inf
qfactor=pi*w.^2.*R./(pi*w.^2-1i.*R.*lambda);
else
qfactor=1i*pi*w.^2./lambda;
end
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