We show, using semiclassical measures and unstable derivatives, that a smooth vector field $X$ generating a contact Anosov flow on a $3$-dimensional manifold $\mathcal{ M}$ has only finitely many Ruelle resonances in the vertical strips $\{ s\in \mathbb{ C}\ |\ { \rm Re}(s)\in [-\nu_{ \min}+\epsilon,-\frac{ 1}{ 2}\nu_{ \max}-\epsilon]\cup [-\frac{ 1}{ 2}\nu_{ \min}+\epsilon,0]\}$ for all $\epsilon>0$, where $0<\nu_{ \min}\leq \nu_{ \max}$ are the minimal and maximal expansion rates of the flow (the first strip only makes sense if $\nu_{ \min}>\nu_{ \max}/2$). We also show polynomial bounds in $s$ for the resolvent $(-X-s)^{ -1}$ as $|{ \rm Im}(s)|\to \infty$ in Sobolev spaces, and obtain similar results for cases with a potential. This is a short proof of a particular case of the results by Faure-Tsujii in \cite{ FaTs1,FaTs2,FaTs3}, using that $\dim E_u=\dim E_s=1$.
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