Study Of Terahertz Time-domain Spectroscopy Based On Fiber Laser

The THz band is an area of convergence between the electronics field and the photonics field.Thus it has many unique properties such as low energy,coherence,high penetration,transient,spectral resolution,and hydrophobicity.In recent years,terahertz waves have been widely used in food safety testing,drug analysis,defense technology,and communication.Terahertz Time-Domain Spectroscopy(THz-TDS)is increasingly used in people's life,and this system trends to be miniaturized,compact,portable and commercial.So this is the cause of the project.The research work of this paper mainly includes the following content:The hardware part contains three major sections.First,the photoconductive antenna method is adopted to generate THz waves while equivalent time sampling principles is adopted to detect THz pulses.Second,study on the coupling efficiency of optical fiber in free space.The matching conditions of beam parameters and fiber collimator characteristic parameters are theoretically analyzed and the parameters of the beam are measured based on the knife edge method to further simulate the transmission of Gaussian beam in free space.Adjusting the fiber collimator so as to improve the coupling efficiency of the Gaussian beam in the fiber.The influence of the coupling alignment error on the coupling efficiency is analyzed from theory to practice.Third,two kinds of optical delay line systems are raised.The setup is finally completed and their stability,delay accuracy and coupling efficiency are tested.Further more,the experimental results are compared and analyzed.The software part contains : The virtual instrument software LabVIEW is used to realize the communication and control of the computer and the hardware equipment of the system,which also realize the function of the stepping motor scanning,the data acquiring,and the display of the THz time domain and frequency domain waveforms.System optimization : After completing the construction of terahertz time-domain spectroscopy system of fiber laser.The effects of bias voltage,modulation frequency,pump light power,probe light power,lens position and photoconductive antenna on terahertz time domain and frequency domain waveforms are analyzed,and the optimal signal to noise ratio and optimized parameters are obtained by experiments.which can provide some technical support for the realization of system instrumentation.