The Research Of Terahertz Imaging Technology Based On Compressive Sensing

The terahertz wave is a general term for electromagnetic waves in the frequency range of 0.1 to 10 THz.It combines some characteristics of microwave and infrared waves,with low photon energy,penetration selectivity,fingerprint characteristics,water sensitivity and other characteristics,which provides terahertz imaging a broad application prospects in biomedical,security,industrial testing and other fields.However,the terahertz-band detection means are relatively scarce,unable to achieve real-time imaging,which greatly restricts the development of terahertz wave imaging technology.Compressive sensing technology is based on a new signal sampling theory.It can achieve the recovery of the signal far below the Nyquist sampling rate,thus the data sampling time is significantly reduced.Therefore,applying the compressive sensing technique to terahertz wave imaging can shorten the sampling time and greatly reduce the imaging time.Moreover,two-dimensional imaging can be realized quickly with a single detector by this method,and it has the advantages of fast imaging speed,low cost,simple structure and so on.This thesis mainly introduces a terahertz wave imaging system based on compressive sensing technology.The practicality of the imaging system has been analyzed theoretically and experimentally.The factors affecting the image quality have been analyzed.Furtherly,the imaging structure for improving imaging quality of compressive sensing has been designed.The main innovations of the thesis include:1.A metal mask structure that shares the adjacent mask matrices has been designed with the modulation depth of 100%.It greatly simplifies the complicated process of making a large number of mask plates,and improves the switching speed of the mask matrices,and eliminates the problem that the optical path is not aligned in the switching process.2.A terahertz-wave imaging system with a range of 1.0-2.2 THz has been realized by combining a compact,tunable terahertz parametric oscillator source with compressive sensing imaging.It provides a path for the development of miniaturized terahertz wave imaging system.3.An imaging structure combining transmission and reflection mode has been designed to solve the problem of poor stability of terahertz radiation.The sum of the radiation measured by two detectors simultaneously is the total intensity from the THz source to the mask plate and it can be normalized to eliminate the influence of poor radiation stability on the imaging results.While two-path data is subtracted to each other,it plays a role in improving the modulation depth,and further improves the imaging signal to noise ratio.4.The compressive sensing imaging of biological tissue samples with terahertz wave has been investigated.Terahertz wave has an extremely broad prospect in biomedical imaging.The application of compressive sensing technology in biomedical area greatly reduces the imaging time,and provides an important method for the exploration of rapid biomedical imaging of terahertz wave.