In this paper, a terahertz axicon (n=1. 55) with a base angle of 10 degrees is designed, introduced into a Terahertz Time domain spectroscopy(THz-TDS) (0. 1-1THz), and a transmission beam scanning experiment is built. At each waveform of the raster scan of each section, the spectrum is calculated using a Fast Fourier Transform (FFT) to obtain the beam cross section for each frequency. The measured central beam width at different frequencies varies between 7mm and 2. 5mm, and the distance between the measurement plane and the tip of the axicon is 80mm; by numerically processing the information of each plane, the beam reconstruction results at different frequencies can be obtained. From the analysis results, it can be seen that the THz-TDS can generate non-diffracting beams with depth of field exceeding 160mm via an axicon with a base angle of 10 degrees, the central spot width does not exceed 7 mm, and there are almost no side lobes. The results show that the Bessel beam can provide a significant depth of field expansion capability for the THz-TDS, which will have a positive impact on the non-destructive testing of samples with large thickness and uncertain defect locations.
PC materials have been widely used in medical equipment, automotive manufacturing, aerospace, electronics and other fields, and its thickness detection has become an important part of its quality control. In this paper, based on the thickness detection requirements of PC materials, the propagation characteristics of THz waves in PC materials are simulated, and a pulsed terahertz reflection system is built. The PC materials of different thicknesses are sampled and their single-point waveforms are obtained as actual detection signals. Using the deconvoluted air signal as input, the optical parameters of PC material extracted by transmissive method, the propagation simulation model of THz wave in different thickness PC materials is established, and the simulation waveform is simulated from three aspects: flight time, waveform and amplitude. Compare and analyze the actual detected waveform.
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