# how to generate a chirp pulse and obtain its phase

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dang khoa tran on 22 Feb 2020
Answered: Priyanshu Mishra on 26 Feb 2020
Hi,
I would like to generate figure showing the a chirp pulse with the Gaussian envelope ( in the code) and to obtain its phase. I have execute the below code but it does not work. Because if it is correct, the spectrum should have the same shape as shown in the attached figure.
So does anyone have any idea on that?
This is the code I use:
c=3*10^8; %the speed of light
fs=10^-15; %femtosecond
nm=10^-9; %nanometer
Fs=2.35*10^16; % Sampling frequency = 10*50Hz
Ts=1/Fs; % Sampling interval
carrier_fre=2.35*10^15; %%(Hz)
t=-0.8*10^-13:Ts:0.8*10^-13; % Sampling time instants [s]
t0=0*fs; %%time
tau=40*fs; %%pulse duration
phi=exp(j*carrier_fre*t)
E_field=exp(-2*log(2)*((t-t0)/tau).^2)*phi; % The gaussian envelope
E_phase=angle(E_field);
%% Plot the spectrum
figure;
subplot(2,1,1),plot(t,E_field);
axis([-inf,inf , -inf,inf])
xlabel('time');ylabel('E (a.u.)');
title('spectrum without carrier frequency');
subplot(2,1,2),plot(t,E_phase);
axis([-inf,inf, -inf,inf])
title('Phase');
##### 2 CommentsShowHide 1 older comment
dang khoa tran on 22 Feb 2020
In fact, I also try this f0=2.35E15 at t but how to identify the f1 at t1 if it is a up-chirp? And how to obtain the phase of this chirp?

Priyanshu Mishra on 26 Feb 2020
Hi Dang,
To generate a chirp pulse, you may refer to following link.