Study On The Key Problems And Applications Of Terahertz Photoconductive Devices

Photoconductive terahertz emitters and detectors are a sort of optoelectronicsdevices having high stability and high integration, and become the most widely usedterahertz devices. Due to the relative low output power and low detection sensitivity,however, these kinds of terahertz devices have been impeded to further apply in otherareas, such as terahertz communication and terahertz radar. Therefore, how togenerate and detect terahertz wave with high efficiency are the most important issuesfor now.In this thesis, the pulse terahertz wave photoconductive antenna and continuewave terahertz photomixer are mainly studied. Their working principle andcharacteristic performance have been investigated detailedly. These results provide aguideline to improve the radiation power and extend frequency spectrum. In addition,the terahertz detection methods including free space electro-optic sampling andphotoconductive antenna sampling have been investigated. Based on the detectionprinciple, a differential electro-optic detector with high signal-to-noise-ratio and highsensitivity has been designed. The detailed content of this thesis are listed as follow:(1) The ultrafast dynamics of femtolaser pulse with photoconductive material hasbeen investigated, which interpreted the space-charge screening of bias voltage inphotoconductor. Based on the fundmental dipole radiation theory, the terahertztime-domain pulses generated from small-gap photoconductive antenna indifferent laser widthes and carrier lifetimes have been calculated numerically.(2) Based on the electromagnetic boundary condition of large-gap photoconductiveantenna, the radiation mechanism and terahertz waveform in different pump laserpowers of large-gap photoconductive antenna has been calculated. These resultsrevealed the power saturation effect of large-gap photoconductive antenna.(3) The working principle of continue-wave terahertz photomixer has beeninvestigated. By using finite-element-method, the interdigatated finger capacitanceof photomixer with different finger parameters has been calculated. Based on the results, we can fully understand the dependence between device configurationsand finger capacitance and provide a guideline to optimize the experimental work.(4) For the free space sampling method, a terahertz electro-optic differential detectorwith high signal-to-noise-ratio and high sensitivity has been proposed. By usingthis newly-designed detector, the terahertz pulse has been detected successfully.(5) Based on the convolution theory, the waveforms of the detected terahertz pulse byusing photoconductive antenna in different laser widths and different carrierlifetimes have been calculated. The results show that the detected waveform andactual waveform of terahertz pulses are different. This phenomena resulted fromthe finite response speed of detected antenna, thus, can lead to interprete the“filter” and “distortion” effect.