  We demonstrated characterizing the electric field waveform of multi-terahertz
pulses (10-50 THz) as vector quantities in the time domain by applying the
polarization modulated electro-optic sampling (POMEOS) method. The problem of
an ultrabroadband gate pulse was solved by modifying the fitting function in
POMEOS and its validity was confirmed through numerical simulations. High
accuracy and precision of approximately 1 mrad with 3 s accumulation were
demonstrated. Our method can be applied not only to multi-terahertz
polarization measurements for linear response but also to the evaluation of the
driving field of intense pulses for nonlinear response or material control.
