  We observed the scintillation pattern of nine bright pulsars at 324 MHz and
three at 1.68 GHz and analyzed the wavenumber spectrum which is related to
electron density variations of the plasma turbulence of the interstellar
medium. For all pulsars the frequency section of the autocorrelation function
of the dynamic spectra to at least 45\% of the maximum corresponds to
predictions of scattering theories with a range of power-law exponents of the
wavenumber spectrum of $3.56 \leq \alpha \leq 3.97$ with errors $\leq 0.05$ and
a mean with standard deviation of $3.76\pm0.13$. The range includes
$\alpha=3.67$ for the Kolmogorov spectrum. Similar results although with larger
errors were found from the Fourier transform of the autocorrelation functions
down to $\sim 10^{-3}$ of the maximum. No clear case of a distinction between
thin-screen and extended-medium scattering models was found. The average
frequency profile of the scintles can be characterized for steep wavenumber
spectra with $\alpha\lesssim4$ by a cusp with a somewhat rounded peak. For
flatter spectra, down to at least $\alpha\sim 3.56$ the cusp with its peak
becomes more pronounced and its decay steepens. We discuss our findings in the
context of scattering characteristics of the interstellar medium.
