SPECKLE computes size of speckle pattern

SYNTAX; speckle;

by Chuck DiMarzio Northeastern University August 2009

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Light from a laser is focused to a spot on a ground glass. We want to know the size of the speckles on a screen some distance away.

Contents

Set parameters

lambda=532e-9; % Doubled Nd:YAG
d0=2.7e-6/2;     % Waist diameter with NA=0.25
b=pi*d0^2/4/lambda; % Rayleigh range
z=(-5:0.05:5)*b;    % Vary z through focus
zscreen=0.3;      % Distance to screen
%

Compute beam diameter at glass, speckle diameter, and plot

dglass=d0*sqrt(1+(z/b).^2); % beam diameter on the glass
dspeckle=4/pi*lambda./dglass*zscreen;  % speckle diameter on the screen
%
fig1=figure;plot(z*1e6,dspeckle*1e3);grid on;
moose=axis;
axis([moose(1:2),0,moose(4)]);
xlabel('z, Distance from Focus, \mu m');
ylabel('d_{speckle}, mm');