Figure 5: Z-scan and FTIR measurements.
From: Terahertz saturable absorbers from liquid phase exfoliation of graphite
(a) Schematic diagram showing the open aperture z-scan setup; (b) beam waist (radial spot size) profile measured at different positions along the optical axis z, of the single-plasmon 3.5 THz QCL operating in pulsed-mode with a pulse width of 2 μs, a modulation frequency of 200 kHz, under an applied field of 7.6 kV cm−1. The error bars represent the uncertainty associated with the measurement of the radius of the beam spot. The fitting function 
allows to retrieve a radial spot size w0∼95±6 mm. (c,d) FTIR transmittance of (c) Eth-GSA and (d) W-GSA normalized to the transmittance of the SiO2/Si substrate, in the NIR, MIR and THz spectral ranges. The spectra collected separately in the three spectral ranges are plotted together. A white light source is employed in all cases combined with a PbSe detector (NIR) DTGS KBr detector (MIR) and DTGS-polyethylene detector (THz).
