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Entry   Finesse vs power by difference between main and second resonance, posted by Loïc Amoudry at Optical room about lasers and optics CrossSecondaryResonance.mGetCavity.m
    Reply   Finesse vs power by difference between main and second resonance, posted by Loïc Amoudry at Optical room about lasers and optics 
    Reply   Finesse vs power by difference between main and second resonance, posted by Loïc Amoudry at Optical room about lasers and optics 
Message ID: 12     Entry time: Wed Oct 31 11:36:30 2018     Reply to this: 15   16
 Author: Loïc Amoudry 
 Status: Fixed 
 Type: report 
 Category: lasers and optics 
 Location: Optical room 
 Title: Finesse vs power by difference between main and second resonance 

Measurements show that ratio decrease versus power. BUT, the second resonance measurement induce lower power in the cavity so the ratio is not directly true.

Also, simulation of the main/second resonance power by Pierre's simulation has shown ratio ~50, ~47.6 and 43.5 respectively for 0A, 2A and 4A.

I (A) Main resonance (mW) Second resonance (mW) Ratio
0 8.07 0.416 19.4
2 121 6.77 17.9
4 324 20.2 16

 

Attachment 1: CrossSecondaryResonance.m  2 kB  | Hide | Hide all
clear all; close all;
tic
addpath(genpath('C:\Users\amoudry\desktop\Fichiers Labo\Fichiers Pierre\Simulation\Personal codes\Various'))
[TAS,~,r] = GetCavity('SBOX_ULE');
[F,~] = Get_info(TAS(1:4),TAS(5:8),TAS(9:12));
lambda = 1030e-9;
c = 299792458;
FSR = 133.33e6;
w0 = 2*pi*c/lambda;
tau = 1e-12; % FWHM duration
a = 4*log(2)/tau^2;
E0 = 1;%(pi/2/a)^(1/2); % Energy to normalize gaussian spectrum (Input beam power = 1)
DeltaPhiCE = 0; % CEP
N = 1e5;

dk = 0:(N-1);
Aa = (r.^dk-r.^(2.*N-dk));
Bb = E0*TAS(1)./(1-r.^2);
Cc = (1-r.^(2.*N));

Nn = 5e2; % Increase Nn <-> increase resolution
dtt = -Nn:Nn;
dtt = dtt*lambda/c/(0.1*Nn); %1e6
Ecn = zeros(numel(dtt),1);
for ii = 1:numel(dtt)
    for ll = 0:3
%         ll = 0;
        dt = dtt(ii)+ll*lambda/c;
        Phid = DeltaPhiCE + w0.*dt;
        temp_vect = Aa.*cos(dk.*Phid).*exp(-a.*dk.^2.*dt.^2./2);
        Ecn(ii,ll+1) = Bb.*(2*sum(temp_vect)-Cc);
        disp([num2str(ii)]);
    end
end
toc
%% Time plots
% figure
% semilogy(dtt/lambda*c,Ecn/max(Ecn),'LineWidth',2)
% hold on
% semilogy(dtt/lambda*c,Ecn2/max(Ecn),'LineWidth',2)
% hold on
% semilogy(dtt/lambda*c,Ecn3/max(Ecn),'LineWidth',2)
% hold on
% semilogy(dtt/lambda*c,Ecn4/max(Ecn),'LineWidth',2)
% set(gca,'FontSize',15)
% xlabel('\DeltaT (\lambda/c)')
% ylabel('Energy (A.U.)')
% grid on
% legend('\DeltaT = 0','\DeltaT = \lambda/c','\DeltaT = 2\lambda/c','\DeltaT = 3\lambda/c')
% axis square

% figure
% semilogy(dtt/lambda*c,Ecn/max(Ecn),'LineWidth',2)
% grid on
% set(gca,'FontSize',25)
% % set(gca,'YLim',[1e-9 1e0])
% xlabel('\DeltaT (\lambda_0/c)')
% ylabel('log(Energie (u.a.))')

%% Frequency
nu0 = w0/2/pi;
frep = (1/FSR-nu0/FSR*dtt).^(-1); % Infinity in dtt = 1/nu0

fprintf('\nFinesse : %g\n\n',F);
% Get linewidth
figure
for jj = 1:4
%     Find the 2 minimas of Ecn_half. Take the corresponding frep and
%     substract them
    Ecn_half = abs(Ecn(:,jj)-max(Ecn(:,jj))/2);
    Ecn_half2 = sort(Ecn_half);
    [row1,~] = find(Ecn_half==Ecn_half2(1),1);
    [row2,~] = find(Ecn_half==Ecn_half2(2),2);
    if numel(row2)>1  % Sometimes row can be a vector
        row2 = row2(2);
    end
    dnu = abs(frep(row2)-frep(row1));
    fprintf('RES %g\nMax gain : %g. Linewidth : %g kHz\n\n',jj-1,max(Ecn(:,jj)),dnu/1e3);
    
%     plot((frep-FSR)/FSR,Ecn(:,jj)/max(Ecn(:,1)),'LineWidth',2)
%     hold on
    semilogy((frep-FSR)/FSR,Ecn(:,jj)/max(Ecn(:,1)),'LineWidth',2)
    xlim([-0.05 0.05])
    hold on
end
set(gca,'FontSize',15)
xlabel('(f_r_e_p-FSR)/FSR')
% ylabel('Energy (A.U.)')
ylabel('log(Energie (u.a.))')
grid on
legend('\DeltaT = 0','\DeltaT = \lambda/c','\DeltaT = 2\lambda/c','\DeltaT = 3\lambda/c')
axis square
% axis([-0.01 0.01 10^-6 1])
Attachment 2: GetCavity.m  1 kB  | Hide | Hide all
function [TAS,r,r_prod] = GetCavity(cav_name,varargin)
% Return T and r coefficient of a given cavity
% TAS vector contains the 4 T coeffs, then 4 A coeffs, then 4 S coeffs

if strcmp(cav_name,'SBOX_ULE')==1
    TAS(1) = 180e-6;   % T
    TAS(2) = 2e-6;
    TAS(3) = 2e-6;
    TAS(4) = 2e-6;
    TAS(5) = 1.15e-6;  % A
    TAS(6) = 1.27e-6;
    TAS(7) = 1.2e-6;
    TAS(8) = 1e-6;
    TAS(9) =  7e-6;     % S
    TAS(10) = 4.5e-6;
    TAS(11) = 3.6e-6;
    TAS(12) = 9e-6;
%     TAS(1) = 180e-6;   % T
%     TAS(2) = 3.2e-6;
%     TAS(3) = 2.8e-6;
%     TAS(4) = 2.85e-6;
%     TAS(5) = 30e-6;  % A
%     TAS(6) = 30e-6;
%     TAS(7) = 30e-6;
%     TAS(8) = 30e-6;
%     TAS(9) = 20e-6;     % S
%     TAS(10) = 20e-6;
%     TAS(11) = 20e-6;
%     TAS(12) = 20e-6;
    
elseif strcmp(cav_name,'ThomX')==1
    TAS(1) = 120e-6;   % T
    TAS(2) = 1.5e-6;
    TAS(3) = 1.5e-6;
    TAS(4) = 1.5e-6;
    TAS(5) = 0.4e-6;  % A
    TAS(6) = 0.24e-6;
    TAS(7) = 0.24e-6;
    TAS(8) = 0.27e-6;
    TAS(9) = 4e-6;     % S
    TAS(10) = 4.5e-6;
    TAS(11) = 10e-6;
    TAS(12) = 4.5e-6;
    
elseif strcmp(cav_name,'MIGHTY_low')==1
    TAS(1) = 1060e-6;
    TAS(2) = 330e-6;
    TAS(3) = 330e-6;
    TAS(4) = 330e-6;
    TAS(5:12) = 0;

elseif strcmp(cav_name,'Fab_cav')==1
    TAS(1) = 100e-6;
    TAS(2) = 10e-6;
    TAS(3) = 10e-6;
    TAS(4) = 10e-6;
    TAS(5:12) = 0;
end

switch nargin
    case 2
        TAS = repmat(TAS,numel(varargin{1}),1);
        TAS(:,1) = varargin{1};
    case 3
        TAS = repmat(TAS,numel(varargin{1}),1);
        TAS(:,1) = varargin{1};
        TAS(:,2) = varargin{2};
end
    
% Field reflection coeffs
rr = @(TAS) (1-sum(TAS,2)).^(1/2);
for ii = 1:4
    r(:,ii) = rr(TAS(:,ii:4:12));
end
r_prod = prod(r,2);
end
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