Polarization-variable emitter for terahertz time-domain spectroscopy

Large-area photoconductive switches as emitters of terahertz pulses with fully electrically controlled linear polarization

Polarimetric measurements in the terahertz (THz) range have a wide range of applications in material science and physico-chemistry. Usually performed using mechanically controlled elements, such measurements are inherently limited in precision and acquisition rate. Here, we propose and realize an innovative concept of a THz pulse emitter, linearly polarized, which allows electrical continuous control of the polarization direction and modulation ability up to several tens of kHz. It consists in an interdigitated photoconductive switch with an intermixed sickle geometry, where the vertical and horizontal components of the electric field are intermixed at a subwavelength scale. We demonstrate that such an emitter permits control of the direction and amplitude emitted with an excellent degree of polarization up to 4 THz, which is estimated to be experimentally better than 98%. This work opens perspectives for sensitivity improvements in THz polarimetry with lock-in detection schemes.

A dual-port THz Time Domain Spectroscopy System optimized for recovery of a sample's Jones matrix

We describe the design, build and characterization of a novel two-output port configuration for a THz-Time Domain Spectroscopy (TDS) system. By introducing a tilted THz ultra-broadband polarizer, we split the THz beam in two orthogonal polarization detector branches. The probe laser is similarly split (with an optical polarizer) replicating the detection chain to obtain two independent orthogonal polarization detection units. We describe the system's performance highlighting some of the advantages of this system in one of its two modes of operation: optimized polarimetry for Jones matrix measurements. A bi-refringent sapphire standard was measured to confirm its capabilities and assess the performance of the system showing good agreement with existing literature data.