We present the realization of a traveling-wave electrical pulse generator using pure nonresonant instantaneous optical rectification in bulk GaAs. The optical excitation was achieved by far-infrared pulses of 1–6 ps duration in the wavelength range from 8 to 15 μm, generated by a free-electron laser. The coupling of the optical rectification polarization into the fundamental mode of the microstrip transmission line is verified by angle-resolved measurements. Since optical femtosecond pulses are now becoming readily available, this alternative technique, which gains in efficiency at shorter pulses, may find growing importance for ultrafast pulse generation. © 2000 American Institute of Physics.