Improvised design of THz spectrophotometer using LT-GaAs photoconductive antennas, pyroelectric detector and band-pass filters

Abstract

We report the improvised design of LT-GaAs photoconductive antenna and pyroelectric detector-based terahertz (THz) spectrophotometer by introducing band-pass filters. The spectrophotometer provides direct optical/absorption information of materials in THz domain without using any signal processing devices (such as lock-in amplifier) and delay arrangement, etc., which are required in conventional THz spectrometer. Moreover, obtained absorption results from spectrometer are less affected by laser fluctuations and inherent noises of the detector. The laser pulses of duration ~15 fs at 80 MHz repetition rate are utilized in this spectrometer to generate THz radiation with good conversion efficiency (η) of the order 3 × 10−3. In addition, emphasis is also given to understand the effect of single- and two-photon absorption on generated THz power with respect to incident laser power density. Absorption properties of packing materials such as paper, Teflon, transparency and rubber (eraser) sheets are investigated in terms of their attenuation coefficients and absorbance at 0.5 and 1.5 THz region in our newly designed THz spectrophotometer. Our study demonstrates the significant information about their attenuation coefficients lying between 300 and 5000 dB/m. The attenuation in THz power has been measured as a function of the paper thickness (0.3–1.5 mm). The obtained results show the exponential growth in absorption with respect to paper thickness.