The Motion Control And Data Acquisition Of Terahertz Time Domain Spectroscopy

THz wave is a kind of electromagnetic wave whose frequency ranges from0.1THz to10THz. In the last20years, thanks to the rapid development of ultrafast laser technology,THz-TDS as a new and rapid developing spectral analysis method is concerned in manyareas. To get the time-domain waveform and the frequency-domain spectrum, I haveprogrammed a set of procedures about motion control and data acquisition in THz-TDS. Asit’s easy to control move and fast to collect and process data completely, this software hasgood practical value. The followings are this thesis’s main research work.As I have participated in building the light path of transmissive terahertz time domainspectroscopy system, so I could deeply analyze the functional requirements of motioncontrol and data acquisition for programming. And I have programmed a set of proceduresmainly about motion control of stepper translation stage and data acquisition and processingof lock-in amplifier by LabVIEW, which have successfully realized the synchronization ofthe change of optical path’s difference and the time domain data’s acquisition, and moreovercompleted the real-time fast fourier transform of the time-domain waveform to obtainspectrum.In order to prove the procedures’ correctness, I design the corresponding experiment.First I put the PTFE sample into THz-TDS to be detected, finding that there is a1.12ps timedelay between sample’s signal time-domain waveform and reference’s, which proves thatthe measured signal is terahertz signal and the procedures of time-domain data acquisition iscorrect. Then I import the measured time-domain data into the Oringin software to be fastfourier transformed, finding that the frequency-domain spectrum FFT by Oringin is as sameas FFT by LabVIEW, which proves that the LabVIEW FFT procedure is feasible. Finally, Ianalyze the bandwidth from the frequency-domain spectrum, and design the dual-pumpexperiment to obtain THz wave whose bandwidth is increased from2.75THz to5.2THz.To make the optical path’s building and debugging more conveniently, and to makeoptical system more simple and compact, I design the appropriate mechanical partsaccording to actual needs, such as the cursor-plate part which is used to calibrate the opticalpath’s height, the crystal-box device which is used to clamp the detected crystal, and the45-base folder device which is used to clamp the mirror and so on.