I know that the Laplace transform of a signal is

$X(s)= \frac{1}{s^2+6s+8}$

$ ROC = $ {s|-4 < Re{s} < -2}

therefore $x(t) = -\frac{1}{2}\cdot (e^{-2t}\cdot u(-t) + e^{-4t}\cdot u(t))$

$u(t)$ is the heaviside function.

I need to find its Fourier transform (or to prove why there is not such transform).

by wolfram alpha I see that the Fourier transform doesn't exist for this signal.
Someone here can explain why ?

Thank you :)