Terahertz Near-field Real-time Spectral Imaging And Its Application In Information Detection

Terahertz waves refer to electromagnetic waves with a frequency between 0.1-10THz(1THz=1012Hz)and a wavelength range of 3mm-30?m,which is between infrared and microwave.Terahertz is the last frequency band in the electromagnetic spectrum that has not been fully exploited and is called the "THz gap".With characteristics such as broadband,transient,low energy,penetrability and fingerprint spectrum,terahertz waves have broad application prospects in disciplines including astrophysics,wireless communication,biomedicine,etc.Terahertz imaging is one of the most important applications in the field of terahertz science and technology.Compared with other imaging methods,due to the characteristics of terahertz waves,terahertz imaging can non-destructively obtain rich information including the refractive index and electrical conductivity of the sample,which is of great significance in the fields of biological tissue differentiation,military security inspection,and non-destructive testing.This article focuses on terahertz imaging,mainly in the following aspects:?.In order to achieve the imaging goals of super-resolution,high frame rate and taking into account spectral information,a set of terahertz near-field real-time spectral imaging system was built.The system is based on the transmission type terahertz time-domain spectroscopy system,and the optical path design is modularized.The system is composed of pump,probe,near-field detection,electro-optical sampling and image acquisition.The measured terahertz electric field intensity can reach up to 600KV/cm,and the terahertz spot diameter ranges from 500?m-4mm.As a terahertz time-domain spectroscopy system,its signal-to-noise ratio is high,and the spectrum bandwidth can reach 3THz.? The system is improved by means of time-domain dynamic subtraction,spatialdomain differential detection,which greatly improves the signal-to-noise ratio.The metal structure including letters and resolution targets was used to evaluate the resolution of the system.The resolution of the imaging system can reach 20?m,far exceeding the diffraction limit of traditional imaging systems.The real-time frame rate of the imaging system can reach 20FPS when collecting terahertz images of 512x512 pixels.?.Through the terahertz near-field real-time spectral imaging system,the information detection of the conductive film is realized.Using the system,the pencil writing in the paper sandwich can be read non-contact,and the pencil patterns that are indistinguishable from the background under the optical tape can be distinguished.Compared with the traditional terahertz time-domain spectroscopy(THz-TDS)testing method,the imaging method in this thesis has a convenient measurement process and reliable testing results.The imaging method can not only draw the transmission image of the sample in the terahertz band,but also can obtain a variety of spectral information about different regions of the sample with only one measurement,which shows the superiority of the terahertz near-field real-time imaging over the traditional THz-TDS.