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% Design of a laser cavity with focus on 2 bow-tie resonator
% Notation follows
% "Laser resonators with several mirrors and lenses with the bow-tie laser
% resonator with compensation for astigmatism and thermal lens effects as an
% example" by Haim Abitan and Torben Skettrup 2005 J. Opt. A: Pure Appl. Opt. 7 7
% doi:10.1088/1464-4258/7/1/002
% http://dx.doi.org/10.1088/1464-4258/7/1/002
% The cavity defined by two flat mirrors and distance between them dm
% two concave mirrors with curvatures R1 and R2, and the shortest distance between them d1
% d2 is the beam path length from concave mirror -> flat -> flat -> concave mirror.
% dm is part of d2
% let's set some parameters
R1=0.8;
R2=Inf;
d1=0.2;
d2=1;
Ltot = d1+d2; % total resonator length
% operational wavelength
lambda = 795e-9;
%% let's create cavity abcd matrix
% follow figure 4: elements goes as d1, f1, d3, f2
% where f1 and f2 lens mirror equivalent with f_i=R_i/2
abcd_cavity = abcd_mirror(R2)*abcd_free_space(d2)*abcd_mirror(R1)* abcd_free_space(d1);
if ~isCavityStable(abcd_cavity)
display('Cavity is unstable !');
display('We should stop now. There is no stable mode in this cavity');
error('Not possible to calculate a cavity mode in the unstable cavity');
end
display('Cavity is stable');
zstart = 0;
qstart = abcd2self_repeating_q( abcd_cavity );
zfinal = Ltot;
qfinal = q_after_abcd( qstart, abcd_cavity );
eps = 1e-8; % typical round of error
if ( abs( q2wr(qstart, lambda ) - q2wr(qfinal, lambda) ) > eps )
% We should never be here if above functions do their job correctly
display(qstart);
display(qfinal);
error('The calculation is incorrect: resonator mode sizes do not match at the beginning and the end. Go fix the code.');
end
%% Preparing for the graphical mode output
% time to build the optics set
mirror1.abcd = abcd_mirror( R1 ) ;
mirror1.x = d1;
mirror2.abcd = abcd_mirror( R2 ) ;
mirror2.x = d1 + d2;
optics={mirror1, mirror2};
% display properties setup
lens_width = .03; %Lens width
show_lens_width = 1; %Set to 1 to enable display of lens width on solution propagation plot
show_lens_position = 1; %Set to 1 to enable display of position of center of lens on solution propagation plot
display_prop = [show_lens_width, show_lens_position];
% show beam in the resonator
[waste_at_the_end, radius_at_the_end, waist_at_mirrors] = solution_visualization(qstart,zstart, qfinal, zfinal, optics, lambda, lens_width, display_prop);
waist_at_mirrors
display('Presumed size and location of the cavity waist');
[w0, z0] = cavity_abcd2its_waist_and_position( abcd_cavity, lambda, Ltot )
q0_via_propagation = gbeam_propagation ( z0, qstart, zstart, optics );
[w0prop, R0prop] = q2wr(q0_via_propagation, lambda);
% we expect R0prop to be infinite since it is focused point
% w0prop should match w0
if ( abs( w0 - w0prop ) > eps )
% We should never be here if above functions do their job correctly
display(w0prop);
error('Different methods to calculate focused point parameters do not match');
end
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