| With the development of terahertz science and technology,the demand for high-power terahertz sources is increasing.The gyrotron terahertz source technology is an effective way to achieve high-power terahertz radiation.In addition,the gyrotron based on pulsed high magnetic field can achieve the extreme operating frequency and power and have broad development prospects in the application field of terahertz science and technology.Accurate measurement of its output parameters during the development process is the key to stable operation and efficient light output of the system,but the high-speed time-varying magnetic field causes the gyrotron output signal to have the characteristics of high peak power(W),short pulse duration(μs),and low repetition frequency(single pulse operation),broadband output range(several hundreds of GHz),which bring new challenges to its work and test of the gyrotron.In order to solve these problems,this paper intends to study the broadband instantaneous measurement technology of high-power terahertz radiation to provide technical support for the analysis of working characteristics and parameter measurement of the gyrotron,which mainly includes the following contents:(1)In terms of terahertz frequency measurement,based on Zeeman effect,this paper studies and proposes an ultra-bandwidth terahertz wave frequency measurement scheme using Electron Spin Resoance(ESR)technology to solve the problem that the wide frequency range variation characteristics of the gyrotron.The principle and method feasibility of terahertz wave frequency measurement are clarified,and the spectral characteristics of ESR signal and its influencing factors are revealed.In order to solve the problem that the ESR signal is weak and easily interfered by noise,an ESR characteristic signal extraction method using sparse decomposition adaptive algorithm is proposed.The learned dictionary library was constructed based on the ESR spectrum characteristics,and the reconstruction accuracy of characteristic signals under different signal-to-noise ratios was studied.The signal-to-noise ratio of the weak ESR signal is improved by three orders,and simulation and experimental studies are carried out.(2)A broadband terahertz frequency measurement system was designed and developed,and the measurement bandwidth can be up to 2 THz,which is much better than commercial mixing equipment.The response characteristics of the system were deeply studied under steady and pulse magnetic field conditions.The accuracy,stability,and linearity of the method under different magnetic field gradient conditions were compared through experiments.It can realize continuous terahertz wave measurement with 0.1 %accuracy,99.9 % linearity,and 0.001 % resolution in the range of 0.1-0.7 THz.The simultaneous measurement of continuous terahertz wave with ultra-wideband multi-frequency and the measurement resolution(0.1 GHz)of multi-frequency signals are explored.In addition,a method of introducing a reference signal to improve the measurement resolution under the pulse field is proposed,and the instantaneous measurement of terahertz frequency with narrow pulse(hundred microseconds)is explored,which provides a new idea for pulse terahertz frequency measurement.(3)In terms of terahertz power measurement,in view of the characteristics of pulsed magnetic field gyrotron with high peak power but small energy,a large-size transient and fast-response microbolometer power measurement scheme is proposed.The transient response of the microbolometer is used to measure the pulsed energy、power and pulse width synchronously.The power measurement principle of the microbolometer is expounded,its equivalent model is established,and the relevant theoretical analysis and derivation of the heat balance process are completed.The absorption performance of the metal film in the terahertz band was studied,and the metal Cr film was used to enhance the absorption efficiency of the terahertz wave.A high-power planar detection unit structure and low-noise differential amplifier circuit based on vanadium oxide thermal materials are optimized synergistically from the aspects of thermal response time and the linear output of the electrical signal,and the device was fabricated.(4)In order to illustrate the performance of the microbolometer,the thermal and optoelectronic performance tests of the microbolometer were carried out.It is analyzed and discussed from three aspects of test method,key technology and test result,and completed the corresponding experiment.The results show that the steady-state response and transient response of the device at 208 GHz frequency are 1.18 V/W and 11 V/J,respectively,and the corresponding uncertainties are 1.92 % and 4.47 %.Among them,under transient conditions,three key parameters such as energy,power and pulse width of microsecond pulse high-power terahertz waves can be measured simultaneously,and a terahertz narrow pulse output signal of 25 m J/50 W/500 μs can be realized successfully.(5)Based on the frequency/power measurement technology,the diagnosis of the high pulsed magnetic field gyrotron terahertz wave source is studied.The pulsed magnetic field terahertz gyrotron system developed by the research group has been introduced,as well as a low-loss transmission line for the high-order mode of the gyrotron.The law between the electromagnetic wave mode,frequency,waveguide size and transmission loss in the transmission structure was clarified,and the influence of the eddy current effect on the frequency measurement was analyzed.The research on the instantaneous measurement of its output frequency and radiation power are carried out,and the results of the experiment matched expectations.Finally,the experimental results are compared with the commercial equipment test results.The frequency measurement error is about 0.38%,and the power error is about 10%,which proves the reliability of the measurement technology and provides strong support for the optimization design and state analysis of the gyrotron. |
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