Figure 1.

Schematic of the terahertz time‐domain spectroscopy and its output (THz‐TDS). The THz‐TDS system is based on a terahertz source that emits femtosecond pulses of light. These pulses of light were distributed between the terahertz source, where they were used for sample analyses, and the terahertz detector, where they were used for detecting the terahertz pulses that transmitted through the leaf samples. At the beginning of measurements, a reference signal was recorded. A delay stage was used to change the time delay between the light pulses that were incident on the terahertz source and detector to scan across the terahertz bandwidth. Hedera canariensis and Platanus racemosa samples were measured using a collimated terahertz beam, and Arabidopsis thaliana were measured using a focused terahertz beam (a). For each measurement, a time‐domain reference signal was recorded (E _Ref; blue curve) along with a signal transmitted through the leaf sample (E _Ref; red curve) (b)