Gwenaël Gaborit, Andrius Biciunas, Maxime Bernier and Jean-Louis Coutaz
Based on optical rectiﬁcation in a ZnTe crystal, a terahertz vectorial antenna is here theoretically and experimentally demonstrated. The use of the particular orientation leads to a polarization state angle tunable THz source. This conﬁguration requires only an optical wave plate to manage the impinging optical polarization state,thus adjusting the transverse THz electric ﬁeld orientation. Moreover, the optical rectiﬁcation efﬁciency as well as the THz signal bandwidth remain constant from horizontal to vertical Terahertz polarization. The same crystal, acting then like a THz receiver, allows to perform the vectorial analysis of a THz pulse.
Terahertz (THz) polarization state management is of major interest for many applications such as THz spectroscopy of anisotropic media –, THz ellipsometry –, nonlinear THz studies –, surface plasmon excitation –, or even the dynamic study of biomolecules . THz wave plates are required to adjust the THz polarization state and are made of birefringent media (e.g.,quartz), sub wavelength structures ,  (metallic or dielectric) or even of paper or wood , . These devices are placed along the THz path and can induce losses or spatial shifts. Their orientation (azimutal and even polar angle) have to be precisely adjusted and they are intrinsically narrow band . By using optical rectification (OR) in a nonlinear cubic crystal, we propose to achieve the THz beam polarization tunability by simply adjusting the polarization state of the exciting laser beam, which is much simpler and efficient as it requires only a single optical half-wave plate. Simultaneously, we propose to detect the THz field, with the same efficiency whatever is its orientation, by electro-optic (EO) effect in a similar cubic crystal. Here, the applied THz E-field transforms the isotropic cubic crystal into anisotropic one…
IEEE Transactions on Terahertz Science and Technology · August 2015