  We propose and experimentally prove efficient high-resolution electro-optic
sampling measurement of broadband terahertz waveforms in a LiNbO$_3$ crystal in
the configuration with the probe laser beam propagating along the optical axis
of the crystal. This configuration allows one to avoid the detrimental effect
of strong intrinsic birefringence of LiNbO$_3$ without any additional optical
elements. To achieve velocity matching of the terahertz wave and the probe
beam, the terahertz wave is introduced into the crystal through a Si prism at
the Cherenkov angle to the probe beam. The workability of the scheme at
different wavelengths of the probe optical beam (800 and 1550 nm) is
demonstrated.
