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function [psr_rad]=faraday_vs_B(detuning_freq, Ep, psi_el, B_fields, theta, phi)
% calculates transmission if light polarizations vs B field in the cell
% for given laser probe and B fields array
% Probe field defined by field strength (Ep) and ellipticity angle (pse_el)
% Magnetic field defined by magnitude (B_field) and angles theta and phi.
%
% Note: it is expensive to recalculate atom property for each given B_field strength
% so run as many calculation for constant magnetic field as possible
t0 = clock (); % we will use this latter to calculate elapsed time
%tune probe frequency
detuning_p=0;
N_steps=length(B_fields)
kappa_p =zeros(1,N_steps+1);
kappa_m =zeros(1,N_steps+1);
xi_linear=zeros(1,N_steps);
xi_left =zeros(1,N_steps);
xi_right =zeros(1,N_steps);
% load useful functions;
useful_functions;
% some physical constants
useful_constants;
basis_transformation; % load subroutines
fprintf (stderr, "tuning laser in forloop to set conditions vs detuning\n");
fflush (stderr);
for B_field_cntr=1:N_steps;
B_field=B_fields(B_field_cntr)
% load atom energy levels and decay description
rb87_D1_line;
fprintf (stderr, "calculating atom properties\n");
fflush (stderr);
pfile='atomic_B_field.mat'; % the parent file where B_field is stored. This is the parameter for calculated L0_and_polarization_submatrices
cfile='L0m_and_polarizability_calculated.mat'; % the child file to which calculated matrices are written
need_update=false;
[s, err_p, msg] = stat (pfile);
if(err_p)
%file does not exist
need_update=true;
else
B_field_cur=B_field;
load (pfile); % loading old B_field value
if (B_field ~= B_field_cur)
% old and current B field are different
B_field=B_field_cur;
need_update=true;
else
need_update=false;
endif
endif
[s, err, msg] = stat (cfile);
if(err)
%file does not exist
need_update=true;
endif;
if ( !need_update)
% matrices already calculated and up to date, all we need to load them
load(cfile);
else
% calculate E_field independent properties of the atom
% to be used as sub matrix templates for Liouville operator matrix
[L0m, polarizability_m]=L0_and_polarization_submatrices( ...
Nlevels, ...
H0, g_decay, g_dephasing, dipole_elements ...
);
save(pfile, 'B_field');
save(cfile, 'L0m', 'polarizability_m');
endif
elapsed_time = etime (clock (), t0);
fprintf (stderr, "elapsed time so far is %.3f sec\n",elapsed_time);
fflush (stderr);
global atom_properties;
atom_properties.L0m=L0m;
atom_properties.polarizability_m=polarizability_m;
atom_properties.dipole_elements=dipole_elements;
%light_positive_freq = [wp];
E_field_drive = [0 ];
E_field_probe = [Ep ];
E_field_zero = [0 ];
E_field_lab_pos_freq.linear = E_field_zero + (1.00000+0.00000i)*E_field_probe + (1.00000+0.00000i)*E_field_drive;
% phi is angle between linear polarization and axis x
%phi=pi*2/8;
% theta is angle between lab z axis (light propagation direction) and magnetic field axis (z')
%theta=0;
% psi_el is the ellipticity parameter (phase difference between left and right polarization)
%psi_el=-30/180*pi;
% we define light as linearly polarized
% where phi is angle between light polarization and axis x
% only sign of modulation frequency is important now
% we define actual frequency later on
[E_field_lab_pos_freq.x, E_field_lab_pos_freq.y] = rotXpolarization(phi, E_field_lab_pos_freq.linear);
% we add required ellipticity
E_field_lab_pos_freq.x*=exp(I*psi_el);
E_field_lab_pos_freq.y*=exp(-I*psi_el);
E_field_lab_pos_freq.z=E_field_zero;
E_field_pos_freq=xyz_lin2atomic_axis_polarization(theta, E_field_lab_pos_freq);
wp0=w_pf1-w_sf2; %Fg=2 -> Fe=1
wp=wp0;
light_positive_freq=[ wp];
% we calculate dc and negative frequencies as well as amplitudes
[modulation_freq, E_field] = ...
light_positive_frequencies_and_amplitudes2full_set_of_modulation_frequencies_and_amlitudes(...
light_positive_freq, E_field_pos_freq);
freq_index=freq2index(wp,modulation_freq);
atom_field_problem.E_field = E_field;
atom_field_problem.modulation_freq = modulation_freq;
atom_field_problem.freq_index = freq_index;
problems_cell_array=atom_field_problem;
save '/tmp/problem_definition.mat' problems_cell_array atom_properties detuning_freq ;
fprintf (stderr, "now really hard calculations begin\n");
fflush (stderr);
[xi_linear_i, xi_left_i, xi_right_i]=susceptibility_steady_state_at_freq( problems_cell_array);
%[xi_linear, xi_left, xi_right]=cellfun( @susceptibility_steady_state_at_freq, problems_cell_array);
xi_left(B_field_cntr)=xi_left_i;
xi_right(B_field_cntr)=xi_right_i;
xi_linear(B_field_cntr)=xi_linear_i;
endfor
save '/tmp/xi_vs_B.mat' detuning_freq xi_linear xi_left xi_right E_field_pos_freq E_field_probe B_fields psi_el;
psr_rad=output_faraday_results_vs_B;
elapsed_time = etime (clock (), t0)
return
% vim: ts=2:sw=2:fdm=indent
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