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Fig. 1 | Plant Methods

Fig. 1

From: Non-invasive absolute measurement of leaf water content using terahertz quantum cascade lasers

Fig. 1

a Experimental setup for THz transmission measurements. A current pulser drives a THz cryo-cooled QCL to generate \(2.5 \, \text {THz}\) laser radiation. The laser beam (red straight line in the picture) is coupled to a Fresnel Lens and a Picarin lens to produce a \(8\, \text {mm}\) spot on the plane where the leaf is placed. The leaf is still attached to the plant, and its position is manually controlled. The laser beam transmitted by the leaf is collected by a Golay cell and sent to a lock-in amplifier. b Example of leaf projected area measurement. The picture to be analyzed is made by the fresh leaf with its upper side facing down on a white sheet, and a reference scale (ruler on the right hand side). Fiji ImageJ segmenting line tool was employed to trace the leaf contour and measure the area of the closed figure by using the reference scale. c Measured optical depth as function of the leaf thickness. The experimental data (black squares) are linearly fitted (red straight line), according to the Lambert–Beer’s law in Eq. (4). The linear fit has a coefficient of determination \(R^2 = 0.77\); the slope \(\alpha = 280 \pm 10\, \text {cm}^{-1}\) stems from the absorption coefficient \(\alpha\) of the material, and it is consistent with other absorption coefficients measured for other plant species [16]. The model intercept \(C_0 = 0.05 \pm 0.15\) has a p value of 0.75. Its poor statistical significance enforces the assumption of a Lambert–Beer’s law

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