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Silicon Components in Terahertz Imaging

Jun. 17, 2022

Terahertz waves have low photon energy and strong penetrating ability. Terahertz waves can penetrate non-metallic substances that are opaque in the visible and infrared bands, such as cloth, paper, and plastics. In addition, terahertz scanning imaging has higher spatial resolution. It performs security inspections without touching objects, such as metal blades and pistols. Therefore, terahertz waves provide information that traditional microwave, infrared and other technologies cannot. Terahertz time-domain spectral imaging is used to the fields of diseased tissue detection, non-destructive testing, and safety testing.

Imaging principle

The terahertz wave is focused by the focusing element onto a certain point of the sample. THz lenses collect the terahertz wave transmitted through the sample (or reflected from the sample). It focuses terahertz waves on the terahertz wave detection element. The terahertz wave converts the terahertz signal of the position information contained in the detection element into a corresponding electrical signal. The image processing unit converts this signal into an image. CLZ provides custom THz lenses, that is HRFZ-Si lenses, including hyper-hemispherical silicon lenses, hemispherical silicon lenses and HRFZ-Si silicon meniscus lenses.

Imaging process

After the femtosecond laser passes through the beam splitter, the stronger beam is used as pump light. It is incident on the terahertz emitting crystal to generate THz pulses, which are focused on the detection crystal after passing through the off-axis parabolic mirror. Another weak reflected light is used as the detection light, which passes through the polarizer after multiple reflections. Then it is reflected by the HRFZ-Si lenses to the detection crystal, so that the detection light and the THz pulse pass through the detection crystal collinearly. Thereby indirectly The magnitude of the THz pulsed electric field and its changes are detected. When the detection pulse with the changed polarization state passes through the λ/4 wave plate, it is divided into two beams by the polarization beam splitter. After data processing by the computer, the corresponding optical parameters such as the absorption coefficient of the sample can be obtained.

Terahertz Time Domain Spectroscopic Imaging and Fourier Infrared Spectroscopy

The typical pulse width of the pulsed THz wave is in the scale of picoseconds, which not only facilitates time-domain spectral resolution research on various materials (including liquids, gases, semiconductors, high-temperature superconductors, various biological samples, etc.). It also effectively suppresses the interference of background radiation noise. At present, the signal-to-noise ratio of radiation intensity measurement is much higher than that of Fourier infrared spectroscopy. The stability of radiation intensity from time-domain spectral measurement is better.

CLZ Optical Co., Ltd. provides you with THz lenses(HRFZ-Si lenses) for terahertz imaging technology. Look forward to working with you.