Estimation of THz field strength by an electro-optic sampling technique using arbitrary long gating pulses

We demonstrate a simple approach to retrieve the original peak electric field (E-field) strength of high-intensity THz pulses using an electro-optic sampling (EOS) technique and the Poynting flux approach. The latter supposes assessment of THz pulse intensity by measurement of pulse energy, duration and spot size, but its applicability to a few-cycle THz pulse needs detailed consideration. We applied a deconvolution procedure to the raw EOS data to retrieve the THz field waveform. We describe a two-step procedure that allows us to assess the field strength of an extreme THz field. First, the EOS measurements of the THz field should be performed at low pulse energies to retrieve the THz waveform and estimate pulse duration and amplitudes of each particular oscillation. Next, the field strength of an extreme THz pulse can be assessed from the Poynting flux approach with correction to the abovementioned data obtained from the EOS measurements. We show good experimental coincidence between peak strength estimation from the EOS directly and from the combined approach at 'low' field strength. Hence, an extreme THz E-field strength can also be assessed from preliminary EOS measurements and full energy measurements based on the Poynting flux approach. We also show that the Poynting flux approach for extreme few-cycle THz pulses gives prominent, at least two-fold, underestimation without preliminary EOS measurements.