Series representation of $1/\pi\int_0^\pi e^{\lambda \cos(t)}\cos(nt)dt$

Question

Are there representations of $a_n=1/\pi\int_0^\pi e^{\lambda \cos(t)}\cos(nt)dt,~n\in\mathbb{N},~\lambda\in\mathbb{C}$ as a series?

These $a_n$ are the coefficients of the Laurent series $a_0+\sum_{n=1}^{\infty}a_n(z^n+z^{-n})$ of $\exp(\frac{\lambda}{2}(z+z^{-1}))$.

Thanks!