  We measured polarized far-infrared reflectivity and Raman scattering spectra
of SrCuO$_2$ single crystals. The frequencies for infrared-active modes were
determined using an oscillator-fitting procedure of reflectivity data. The
Raman spectra were measured at different temperatures using several laser
energies $\omega_L$. In addition to eight of twelve Raman active modes,
predicted by factor-group analysis, we observed a complex structure in the
Raman spectra for polarization parallel to the {\bf c}-axis, which consists of
Raman-allowed A$_g$ symmetry modes, and B$_{1u}$ LO infrared-active
(Raman-forbidden) modes of the first and higher order as well as their
combinations. The Raman-forbidden modes have a stronger intensity at higher
$\omega_L$ than the Raman-allowed ones. In order to explain this resonance
effect, we measured the dielectric function and optical reflection spectra of
SrCuO$_2$ in the visible range. We show that the Raman-allowed A$_g$ symmetry
modes are resonantly enhanced when a laser energy is close to $E_0$, while
Raman-forbidden (IR-active) modes resonate strongly for laser line energies
close to the electronic transition of higher energy gaps.
