18. (12 points)
Given that $\left\{ a _ { n } \right\}$ is a geometric sequence with all positive terms, $a _ { 1 } = 2 , a _ { 3 } = 2 a _ { 2 } + 16$.\\
(1) Find the general term formula for $\left\{ a _ { n } \right\}$;\\
(2) Let $b _ { n } = \log _ { 2 } a _ { n }$, find the sum of the first $n$ terms of the sequence $\left\{ b _ { n } \right\}$.