Fig. 2: THz-TDS setup and the THz absorption coefficient of glucose.

Schematic of the THz time-resolved spectroscopy setup. An ultrafast laser source is used to generate THz through optical rectification in a GaP crystal. The detection process uses a partially reflected pulse from the same optical source to perform standard electro-optic sampling (EOS) inside another GaP crystal. In brief, the THz electric field is revealed by resolving THz-induced birefringence in the near-infrared gating pulse, which is monitored as a function of time delay with the THz pulse with a quarter-wave plate (λ/4), Wollaston prism (WP) and a pair of balanced photodiodes (PD). (Inset) Absorption spectrum of a 300 μm-thick glucose (C₆H₁₂O₆) pellet measured with time-resolved THz spectroscopy and featuring a prominent vibrational resonance at 1.43 THz.