Polarization-Sensitive Electro-Optic Sampling of Elliptically-Polarized Terahertz Pulses: Theoretical Description and Experimental Demonstration

Abstract

We review our recent works on polarization-sensitive electro-optic (PS-EO) sampling, which is a method that allows us to measure elliptically-polarized terahertz time-domain waveforms without using wire-grid polarizers. Because of the phase mismatch between the employed probe pulse and the elliptically-polarized terahertz pulse that is to be analyzed, the probe pulse senses different terahertz electric-field (E-field) vectors during the propagation inside the EO crystal. To interpret the complex condition inside the EO crystal, we expressed the expected EO signal by “frequency-domain description” instead of relying on the conventional Pockels effect description. Using this approach, we derived two important conclusions: (i) the polarization state of each frequency component can be accurately measured, irrespective of the choice of the EO crystal because the relative amplitude and phase of the E-field of two mutually orthogonal directions are not affected by the phase mismatch; and, (ii) the time-domain waveform of the elliptically-polarized E-field vector can be retrieved by considering the phase mismatch, absorption, and the effect of the probe pulse width. We experimentally confirm the above two conclusions by using different EO crystals that are used for detection. This clarifies the validity of our theoretical analysis based on the frequency-domain description and the usefulness of PS-EO sampling.

Spatio-temporal imaging of terahertz electric-field vectors: observation of polarization-dependent knife-edge diffraction

“…Since the experimental data were obtained by the EO sampling method, the measured signals correspond to the spatio-temporal integrated signal during the propagation of the probe pulse inside the EO crystal. 29) Therefore, we integrated the calculated results over the Z-direction and probe-pulse propagation time to obtain the theoretical terahertz E-field vector images at different delay times. In this integration procedure, we assumed perfect velocity matching between the terahertz and probe pulses, because the coherence length at the measured terahertz frequency range is estimated to be more than 1 mm, which is the thickness of the ZnTe crystal, according to Ref.…”