Wavelet Transform Terahertz Spectroscopy And Imaging Applications

The terahertz (1THz=1012 Hz) wave, located between millimeter wave and far infrared wave, with the frequency between 0.1THz and 10THz, belongs to far-infrared band (the wavelengths between 30um to 3mm). In recent years,ultrafast laser technology provides a stable and reliable THz pulse source excitation and promotes the applications of THz radiation in many fields.The femtosecond laser excitated coherent THz wave, the THz detection based on the photoelectric effect, constitutes a THz time-domain spectroscopy. The THz time-domain spectroscopy technique is a non-contact measurement technology, a higher SNR to the rapid composition of the sample to make minor changes and differential analysis, and can be measured on the physical material information fast and accurate measurement , such as explosives, drugs, amino acids and other substances THz spectroscopy study. THz time-domain spectroscopy in the practical application of technology in the face of a problem is that the impact of water vapor in the air, theory and experiments show that water vapor in the terahertz frequency range exists strong absorption, usually in the experiment to reduce the moisture content the experimental system is sufficient to nitrogen or experimental system will be pumped into the vacuum, which in practical application is not feasible.One part of this paper's work use the theory of wavelet transform to study how to eliminate the impact of water vapor absorption . In experiment,spectra of seven kinds of samples are measured by terahertz time-domain spectroscopy in both nitrogen and air environment, we used wavelet transform dispose of the survey data under air environment and we obtained a good result. In addition, we got four kinds of samples's imaging and dealed with them by wavelet transform.THz radiation imaging can be used as the signal source objects, in accordance with continuous wave THz imaging is one of its manifestations. THz-ray imaging and X-ray imaging can penetrate clothing, boxes, and other items, but THz-ray photon energy is very low (only a few cents electron volts), can be used on human or non-destructive imaging items.When use continuous wave imaging system to be tested do imaging of using different frequency scanning, imaging clarity different, the characteristics of objects sometimes unclear or details lost, and to get more comprehensive information, the better target identification and testing results, the images obtained by further treatment is necessary.Another part of this paper's work is applying the wavelet transform to THz image processing to extract images on the edge and increase the image information to lay the foundation for further processing, experimental results show that the usefulness of this method.