  We are interested in computing the spectral measure of Laplacean operators in
Paley-Wiener space, the Hilbert space of all square integrable functions having
Fourier transforms supported in a compact set $K$, the closure of an open
bounded set in $\R^N$. I is well-known that every differential operator is
bounded in this space. Among others, we will prove that the spectrum of Laplace
operator is the set $$\{-|x|^2: x\in K\}.$$
