%
%?GS_2D.m
%
%?Calculation?of?a?2D?phase?or?amplitude?hologram?by?using?the?Gerchberg-Saxton
%?algorithm.
%
%?The?program?starts?with?a?plan?wave?（a?phase?hologram?with?all?pixels?set
%?to?the?same?value）?（i.e?an?electric?field）?and?by?iteration?the?operation
%?of?this?hologram?is?increased.
%
%?The?program?use?the?FFT-file?fft2c.m?and?the?inverse?IFFT-file?ifft2c.m
%
%?All?lengths?are?given?in?micrometers.
%
%
%?Orginal?file?was?created?during?the?spring?of?2001?by?David?Engstr鰉?Chalmers
%?
%?Modified?in?November?2002?by?Emil?H鋖lstig?FOI
%

close?all;?%?Close?all?figures
clear?all;?%?Clear?workspace

%?Constants?in?use:


N=256;	????%?The?number?of?sample?points?in?one?direction?（totally?N*N?sampling?points?N
????????????%?should?be?set?to?2^integer?to?increase?the?speed?of?the?FFT-transform）

nr_of_iterations=10;	%?The?number?of?iterations?to?be?calculated

nr_of_phaselevels=128;	%?The?number?of?phase?levels?that?can?be?used
????????????????????????%?OBS!?If?set?to?zero?the?resulting?hologram?will?be?a?
????????????????????????%?pure?binary?amplitude?hologram.

circular_beam=0;		%?1?indicates?that?cross?section?of?the?incoming?beam?is?circular
????????????????????????%?0?means?that?the?whole?hologram?is?illuminated

circular_radie=0.9*N/2;	%?The?radie?of?the?beam?（if?it?is?circular）???????????????????????????


%?**********?Plane?1?-?The?hologram?plane

%?Create?the?original?electric?field?in?plane?1?as?a?homogen?field
%?with?the?amplitude?set?to?one?and?the?phase?set?to?zero?（a?plane?wave
%?moving?along?the?optical?axis）


%?Calculate?the?circular?cross?section?of?the?beam?that?is?used?if?the?variable
%?“circular_beam“?is?set?to?one

X_pos=ones（N1）*（1:N）;
Y_pos=rot90（X_pos-1）;

E_beam?=?ones（N）.*（（N/2-X_pos）.^2+（N/2-Y_pos）.^2
if?circular_beam
????E_plane_1?=?E_beam;
else
????E_plane_1?=?ones（N）;
end


%?**********?Plane?2?-?The?far?field
I_plane2=zeros（N）;							%?The?desired?intensity?distribution
????????????????????????????????????????????%?in?plane?2

%?Just?a?single?pixel?is?set?=>?The?result?（a?plane?wave）?is?given?in?only?one?iteration??????????????????????????????????????????????
%I_hologram（N/2N/2）=1;

%?It?is?possible?to?use?a?ordinary?*.bmp?picture?as?intensity?distribution
%?Just?change?the?filename?to?use?another?image!?
%?OBS!?The?new?image?has?to?be?of?the?correct?size!

%?A?binary?“FOI“
%
[bild?map]=imread（‘FOI.bmp‘）;?

%?Check?the?size?of?the?input?image!
if?size（bild1）~=N
????disp（[‘The?input?image?does?not?have?‘?num2str（N）?‘?rows!‘]）;
????return;
end
if?size（bild2）~=N
????disp（[‘The?input?image?does?not?have?‘?num2str（N）?‘?columns!‘]）;
????return;
end?

I_plane_2_goal?=?ones（N）-double（bild）;
I_plane_2_goal_total?=?sum（sum（I_plane_2_goal））;

E_plane_2_goal?=?sqrt（I_plane_2_goal）;	%?The?E-field?in?the?far?field?（the?phase
????????????????????????????????????????%?doesn‘t?matter）


%?--------------------