| Terahertz(THz)region has been attracted great attention over the last three decades because of its unique optical properties.There are two main techniques for free-space time domain THz field coherent generate and detection,i.e.electro-optic(EO)crystal and photoconductive antenna(PCA).Terahertz time-domain spectroscopy(THz-TDS)basing on optical rectification and electro-optics sampling of the electro-optic crystal is one of the most important and powerful techniques of THz optoelectronics,which is widely used for its advantages of wide spectra,simple structure and easy to operate.In this thesis,our work concentrated on some theoretical and experimental research for a new technique of terahertz time domain spectroscopy basing on optical rectification and electro-optics sampling of the electro-optic crystal and the preliminary study of its transient imaging.It can be outlined as followings:First,we present an improved theory,which considers the nonzero minimal transmission of the used polarizers and the polarization purity of probe laser,and use it to compare the two traditional designs: 45° optical bias and near 0° optical bias on optical modulation depth(OMD),linear dynamical range(LDR)and the ability to cancel optical background noises.Second,we develop a novel design of THz EO detection with crossed polarizer geometry,which combines all the advantages of the two traditional designs.Besides high OMD,the new design exhibits simultaneously large LDR and excellent ability to cancel optical background noises.We also theoretically verified the three advantages of our new design and analyzed the splitting ratio of the non-polarization beam splitter(NPBS)exerts important effect on the optical background noise.Third,we compare the OMD,LDR and the ability of cancel optical background noises of our new design and the traditional near 0° optical bias design experimentally,our new design’s OMD and LDR larger than those of traditional near 0° optical bias design are easily verified experimentally,its optical background noise is seriously effected by the splitting ratio of the NPBS,we developed two broadband non-polarization beam splitters that both can get the well results.Under existing experimental conditions,the new design can get a OMD as 9.8%,which is 2 times larger than near 0° optical bias design,its LDR is also much larger than the latter,the signal-to-noise ratio(SNR)of the available THz waveform is 15.5 times than nearly 0° optical bias design,the background noise elimination ability improve about 34 times by using the NPBS with twenty degrees incidence,which worked well and didn’t limit the application scope.Forth,the single shot terahertz measurement,which is called chirp pulse spectral encoding,is presented by X.-C.Zhang.We applied the new terahertz electro-optic sampling design to this measurement to build a push-pull chirp pulse spectral encoding terahertz pulse single shot measurement system.We carried on the theoretical analysis of the working principle of this new type single shot terahertz measurement system,and compared with the X.-C.Zhang’s traditional spectrum coding method,experimentally verified the new single measurement system can measure the terahertz pulse with high OMD,wide LDR and high SNR.Fifth,we put forward a novel real-time THz imaging system with crossed and balanced structure,which is easy to introduce the terahertz near-field imaging and polarization imaging.We use the new THz imaging system to get the transmission THz imaging of a two-dimensional metal cross and compare it with the tradition real-time difference THz imaging system proposed by X.-C.Zhang,The experimental results show that the new THz imaging system has better performance that the latter at OMD,LDR and SNR.We also introduce the near field measurement to our novel real-time THz imaging system.Finally,we build an implementation scheme of the broadband terahertz pulse transient multi-frames maging system,and make a simulation for the result of the final images. |
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