Validation of Power Linearity in Terahertz Time-Domain Spectroscopy Using a Programmable Step Attenuator

We have constructed a programmable terahertz step attenuator by stacking metallized-film attenuators (MFAs) of different transmittances. Sputter deposition of Inconel alloy on thin polyester films is used to fabricate the MFAs. Good repeatability and flatness of the step attenuator are confirmed in transmittance measurements by a terahertz time-domain spectroscopy (THz-TDS) system. A method to evaluate the linearity of the THz-TDS system is proposed by using the step attenuator over a wide dynamic range. Calibration curves are analyzed by measuring the transmittance of maltose in different concentrations, and the validity of the proposed method is discussed.