Abstract
Using the penetration and transientness of Terahertz pulses and the photoconductive delayed detection method, the tomographic imaging of the interior of the object based on the time of flight can be realized. By comparing the transmittance of several crystals and polymers in the Terahertz band, Polymethylpentene (TPX) was selected as the material of Terahertz lens, and High Resistivity Float Zone Silicon (HRFZ-Si) as the material of beam splitter
Highlights
Terahertz wave is a general term for a specific electromagnetic radiation, between microwave and infrared
The frequency of terahertz wave is between 0.1 THz ~ 10 THz, and the wavelength is between 0.03 mm ~ 3 mm [1]
The window materials used in terahertz wave mainly include High Resistivity Float Zone Silicon (HRFZ-Si) Polymethylpentene (TPX) High Density Polyethylene (HDPE), Picarin (Tsurupica)
Summary
Terahertz wave is a general term for a specific electromagnetic radiation, between microwave and infrared. A femtosecond laser pulse is used to excite the photoconductive crystal to generate photo-generated carriers The photoconductive crystal is excited by the femtosecond laser pulse to generate photo-generated carriers For opaque multi-layer structures in the visible-light range, the penetration of terahertz waves can be used for non-destructive thickness detection, to achieve the transversal resolution of tens of microns (Figure 2). Reflection and refraction occur again at the interface, so that the terahertz signal detected in a time delay window contains multiple reflection peaks, and the thickness of the sample can be calculated according to the time delay between two adjacent reflection peaks [6]. Where d j is the thickness of the jth layer sample; c is the speed of light in vacuum, which is 3 × 108 m/s; nj , nj−1 is the refractive index of the jth layer and the j-1th layer sample; ∆t j is the delay time between the jth and j + 1th reflection peaks
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