The Physical Characteristics Of Superconducting Terahertz Devices And The Setup Of Related Test System

With the rapid development of superconducting technology,the research and application of superconducting devices are also widely carried out.The Josephson effect of superconductors with its oscillating signals in terahertz(THz)band makes various superconducting devices widely used in the terahertz field.To characterize the physical characteristics of superconducting devices in detail and evaluate their performance,two sets of test systems in this paper have established in our lab for studying the spectrum of the microwave radiation of the superconducting device and the physical properties of the superconducting device during their superconducting transition.Terahertz radiation,which covers the frequency range from 1011 Hz to 1013 Hz,has unique characteristics like typical narrow pulse width in the order of picoseconds and low photon energy.It leads to a promising future of applications in various fields such as high-speed communications,radar,astronomy,medical science,non-destructive evaluation and security control.Terahertz detection technology and terahertz radiation source technology have always been the ultimate research direction in the terahertz fieldTerahertz receiver technology(SIR)has always been the most important research direction in terahertz detection technology.Based on the basic heterodyne receiver architecture,the spectrum of the terahertz signal to be measured can be well detected by detecting the intermediate frequency output of the measured terahertz signal and the local oscillation signal.In the current report,the narrowest bandwidth of the signal detected by the terahertz signal based on the SIR system can be as good as 1 Hz.The establishment of such a system will have a very important role in the application of radio astronomy,and in our lab we have used it to evaluate our lab-made high-temperature superconducting Bi2Sr2CaCu2O8+X(BSCCO)terahertz sources.On the other hand,low temperature scanning microscopy(LTSLM)has had many important applications since Sivakov was first proposed in 1996.It uses a low-power laser beam as a perturbation to scan the surface of a sample for a change in some physical factor of the sample.By imaging this kind of change,many physical phenomena can be directly and detailed observed.For superconducting samples,laser irradiation as a perturbation causes changes in the sample voltage and current.Performed can be indirect observation of local superconducting state transition,temperature distribution,thermodynamic properties,and other physical phenomena of superconducting sample by two-dimensional electrical imaging in association with scanning position coordinates.This is very helpful for studying the physical mechanism of various superconducting devices.This paper aims to build excellent test systems to measure various physical properties of superconductors and their working mechanisms,particularly for superconducting terahertz devices.First,we report in this thesis that we build a superconducting terahertz integrated receiver system.Operating frequency band is 300-700 GHz,and the system minimum double sideband noise temperature reaches 290 K.The test process is to analyze the output IF signal when scanning the bias frequency of the flux flow oscillator(FFO)signal to mix with the external signal to be measured.We tested the high temperature BSCCO superconducting terahertz sources with this system.The construction of this system is very important for studying the details of the radiation spectrum of the terahertz source.Second,in this thesis we report the application of a low-temperature scanning microscope system.Post calibration was programmed in order to compensate for the location error during imaging process.The surface of the superconducting device is two-dimensionally imaged with a laser of 1310 nm wavelength by using optical and electrical data.The effect of local thermal effects and superconducting state transition on the performance of the entire device can be investigated.We used this system to measure BSCCO high temperature superconducting terahertz sources and superconducting terahertz modulation devices.In the BSCCO sample,we observed the hot-zone distribution of the sample under high current bias.In the terahertz modulation device,we found that the local normal-state zone formed by non-uniform distribution of current has greatly changed the transmission characteristics of the sample,and the lower thermal relaxation time of the local normal-state zone can make the sample has a higher modulation speed compared with all of the sample turning into normal state.In conclusion,we can get that the establishment of this system is very important for observing and understanding the working mechanism of many superconducting devices.