Application Of Terahertz Time-domain Spectroscopy To Seed Selection In Agriculture And Development Of Femtosecond Optical Pulse Autocorrelator

THz Region occupies the portion of the electromagnetic spectrum between the infrared and microwave bands. Since THz spectrum of materials contains rich physical and chemical information, THz technique has been widely used in many fields, including fundamentel research, industrial and military application. One of the application of THz technique is THz time-domain spectroscopy (THz-TDS). By recording the temporal waveforms of THz pulse, which has been modified by samples, the Fourier transform of the temporal waveform extracts the amplitude and phase spectrum in frequency domain. Subsequently, the absorption and refractive characters of the material may be disclosed.Currently, THz technique for label-free detection of DNA molecule has attracted much attention and shown potential application. The technique has already differentiated double and single stranded DNA molecules, and detected single base mutations on DNA molecules at femtomol levels.In this paper, by using the transmission THz-TDS, we tried distinguishing the different varieties of corn seed by analyzing spectrum of samples. Firstly, we measured and analyzed high resistivity crystalline silicon, different doped crystalline silicon, magnesium oxide, paraffin for suited substrate. Then we measured and analyzed DNA thin film and embryo slice of corn seed in order to differentiate variety. The main results and conclusions are as follows:I. By using the transmission THz-TDS, we measured and analyzed the absorption and dispersion of high resistivity crystalline silicon, different doped crystalline silicon, magnesium oxide, paraffin, and concluded that the high resistivity silicon is ideal substrate material for the transmission THz time-domain spectroscopy measurement of DNA thin film and embryo slice while paraffin is ideal embedding material in the process of making biological samples.II. By using the transmission THz-TDS, we measured DNA thin film and embryoslice of corn seed and derived the amplitude ratio of signal transmitted through sample to reference signal in frequency domain after fast Fourier transform. Resolved characters of the samples are not observed from the experimental results.Ultrashort pulse duration is an important parameter to characterize ultrashort optical pulse. At present, autocorrelator is widely used to measure the femtosecond optical pulse. It has high resolution and sensitivity, compact configuration, and can be adjusted easily. To make an autocorrelator for our laboratory is the second part of this paper. After constructing an autocorrelator, we measured pulse durations of femtosecond laser radiating directly from the Ti: sapphire oscillator and passing through some optical components.We obtained the ideal 8:1 autocorrelation curves. The autocorrelator will be a necessary apparatus for the lab. The measured pulse durations of outgoing from Ti:sapphire laser and passing through lens, polarizing cube beamsplitter offer reference for our laboratory in femtosecond laser experiments.