Why do I have "inside" oscillations when I take the fft of my data

Hi,

I have a data sample that I need to take into the frequency domain, unfortunately I get these oscillations in between the actual negatives and positive values of what I expect, on the left is the sampled signal and on the right the real and imaginary part of its fft.

imag(fftshift(fft(sample)))
real(fftshift(fft(sample)))

Yet what I expect should look like this,

Where did I go wrong about the fft?

Thank you.

[Hugo]

Nevermind, someone already answered that elsewhere, sorry.

https://fr.mathworks.com/matlabcentral/answers/94522-why-do-i-get-a-high-frequency-oscillation-when-i-take-the-fft-of-a-rectangular-pulse?s_tid=answers_rc1-1_p1_MLT

[Mathieu NOE]

hello

well , how does your fft plot looks like if you restraint the x range to -50 / 50 THz ? your plot range is -200 / 200 THz

[Hugo]

Well , that was another issue linked to the fact that I plotted using the angular frequency instead of the frequency. Here is what I get now with all issues solved.

[Mathieu NOE]

glad you found the solution

have a nice day !