The Study Of Terahertz Coherent Tomography Imaging Technique

Terahertz wave is a kind of electromagnetic wave ranging from 0.lT~10THz(3mm~30?m). Terahertz wave can penetrate many kinds of dielectric materials, this property makes terahertz imaging technique very extensive applications. Therefore, limited by wave length of terahertz, the resolution of terahertz imaging is at millimeter level. Combining optical coherent tomography and terahertz ima ging technique, terahertz coherent tomography technique can achieve higher axial resolution theoretically. The main content is listed as follows.(1) Using a thermal radiation terahertz source and Michelson interferometer, a terahertz coherent tomography system is built. Selecting arc mercury lamp with center frequency at 11 THz and 20 THz bandwidth as terahertz source, coherent length which is also know as axial resolution is obtained at 10 micrometer in theory.(2) Editing scanning control and data acquisition program with labview. Through the scanning control program the stepping motor controller can send motion command to the stepping motors, in this way one-dimension and two-dimension scanning for the sample is realized. Data acquisition program control the lock- in amplifier and DAC(data acquisition card) to acquire and process the imaging data. At last the program is verified by scanning the aluminium plate in one-dimension and two-dimension.(3) Scanning the aluminium plate in one-dimension and two-dimension. By fitting one-dimension scanning data the refractive index of aluminium plate under spectrum of arc mercury lamp is acquired, and by processing the two-dimension scanning data the two-dimension image of aluminium plate is obtained. At the same time noise sources of the terahertz coherent tomography system are analyzed, then the sample image is processed with band-pass filter, smoothing, wavelet transforming with Matlab, at last a more sharpen tomography image of aluminium plate is acquired. Analyzing the image acquired it is concluded that this terahertz coherent tomography system has an axial resolution over 100 micrometer.