Over the past few decades THz time domain spectroscopy (THz-TDS) has revolutionized spectroscopy and imaging in this rich region of the electromagnetic spectrum.[1]  THz-TDS directly measures electric field as a function of time, making it excellent for probing the dielectric properties of materials.[1]  The pulsed nature of the technique has allowed it to be extended to study dynamic process with femtosecond time resolution.[2]  To date most THz-TDS spectrometers and imagers just generate and measure linearly polarized THz radiation.  However, the polarization state of a THz pulse can contain as much information as in the amplitude and phase spectra.[3,4]  We have exploited the unique interactions of semiconductor nanowires  to optical and THz photons [4] to designed and realize a compact THz detector that measures the complete state of a THz pulse.[5]  The detector consists of two orthogonal bow-tie antennas fabricated on an insulating quartz substrate.  Each antenna pair is connected by InP nanowires in such a way that the orthogonal antennas are electrically insulated from each other. The polarization selectivity of the nanowires to a gating laser pulse combined with minimal shadowing makes nanowires the ideal photoconductive element in this detector.  Using this detector, we have performed THz polarimetry on THz meta-materials and characterized anisotropic media [5].  The design of our detector eliminates cross-talk between polarization channels and the resulting device also very compact and alignment insensitive. Thus, the cross-nanowire detector can easily replace a standard photoconductive emitter in most THz-TDS systems without significant alteration to the spectrometer or imaging system.

[1] SS Dhillon et al. The 2017 terahertz science and technology roadmap.
J. Phys. D-Appl. Phys., 50:043001 (2017)

[2] CQ Xia, S Ponce, JL Peng, AM Ulatowski, JB Patel, AD Wright, RL Milot, H Kraus, QQ Lin, LM Herz, F Giustino, MB Johnston. Ultrafast photo-induced phonon hardening due to pauli blocking in MAPbI3 single-crystal and polycrystalline perovskites.  J. Phys-Mater., 4:044017 (2021)

[3] CQ Xia, M Monti, JL Boland, LM Herz, J Lloyd-Hughes, MR Filip, MB Johnston. Hot electron cooling in InSb probed by ultrafast time-resolved terahertz cyclotron resonance
Phys. Rev. B, 103:245205 (2021) 

[4] K Peng, MB Johnston, The application of one-dimensional nanostructures in terahertz frequency devices. Appl. Phys. Rev., 8:041314 (2021)  [5] K Peng, D Jevtics, F Zhang, S Sterzl, DA Damry, MU Rothmann, B Guilhabert, MJ Strain, HH Tan, LM Herz, L Fu, MD Dawson, A Hurtado, C Jagadish, MB Johnston. Three-dimensional cross-nanowire networks recover full terahertz state. Science, 368:510–513 (2020)