Research On Efficient Low Pass Filter For Widely-tunable Coherent TGz Source

In recent years,as people have had deeper understanding about the concept of Terahertz,the technology of Terahertz radiation has also been widely applied into various fields of both fundamental and applied researches.It is the advance of Terahertz wave radiation technology that prompts the rapid development of Terahertz technology itself and its related inter-disciplines.The difference frequency method is an efficient way for realizing the production of coherent Terahertz,which means to use two neighboring wave lengths through second-order nonlinear effect in crystal,in a way to produce Terahertz wave.This paper first tested the performance of traditional low pass filters such as black polyethylene and high barrier,with the focus of the wave source of wide tuned beat note Terahertz.Then it made comparisons about its shortcomings and advantages in Terahertz beat note system,ultimately to summarize the deficient points of traditional filters.As a result,this paper will optimize the traditional filters based on structural design of filters of diffraction grating.This paper mainly includes the following viewpoints:1.It has made brief introduction of the characteristics and fields of application of Terahertz wave,as well as several ways of producing radiation in electronics and optics approach.Moreover,it has concluded the development status of wide tuned Terahertz radiation range both at home and abroad,based on organic nonlinear optics approach.2.From the perspective of nonlinear optics and diffraction optics,this paper has induced the basic form of optical difference frequency based on three-wave coupled wave equation.And it has also made analysis of energy conversion process of Terahertz difference frequency;the principle of diffraction optics has laid theoretical foundation for low pass filters of simulated diffraction structures later.3.This paper has also established Terahertz radiation source system of wide tuned difference frequency and tested the performance of traditional low pass filters such as black polyethylene and high barrier.By measuring the transmissivity of black polyethylene(BPE)filter,high barrier/germanium windows and commercial attenuation tablet group based on the above difference frequency source,it has realized to make spectral analysis and imaging application based on the radiation source.4.By designing low pass filters of diffraction structure,which include sawtooth filter(symmetric and blazed grating)and rectangle filter,it has successfully generated the design plan for low pass filter with quite ideal transmissivity and diffraction effect,through simulations with COMSOL software.