Let $X \in \text{Exponential}(\theta)$ be an D214: Exponential random positive real number.
Let $t \in \mathbb{R}$ be a D993: Real number.
Let $t \in \mathbb{R}$ be a D993: Real number.
Then
\begin{equation}
\mathbb{E}(e^{i t X})
= \frac{\theta}{\theta - i t}
\end{equation}