| High-Tc superconducting terahertz(THz)sources are made of Bi2Sr2CaCu2O8(BSCCO)intrinsic Josephson junctions(IJJs),which have advantages like moderate frequency range,tunability,continuous wave,easy fabrication,and so on.Therefore,they have been competitive candidates for THz solid-state emitters,and strongly boosting the developement of THz science and technology.This dissertation focuses on the performance improvements in high-Tc superconducting THz sources by means of structural and practical innovations.The main results are following:1.Holes-inserted BSCCO Stacks.Perturbational method was employed in the THz sources,that we designed and fabricated BSCCO stacks with holes perturbations.Experiment results indicated that there appeared voltage steps on the current-voltage characteristics(IVCs)curves,which meant that holes could arise higher operating voltages,and then increase the radiating frequencies.Therefore,this kind of perturbation provided a way to help optimize the mesa configurations.2.On-chip Temperature Sensing Method.An on-chip temperature sensing method has been initiated by in-situ fabricating sensing tiny junctions on the surface of emitting BSCCO stacks.The stack temperatures could be obtained by comparing the IVCs curves of tiny junctions measured at different emitter biases with those under different bath temperatures.This subject was the first time to obtain the surface temperatures of BSCCO stacks via experiments.3.Terahertz Flashlight.As most of the high-Tc superconducting THz sources have disadvantages like great bulk,high cost and complex system,a compact THz source cooled by liquid nitrogen has been developed,of which the volume is less than 40 cm3.The maximum emission power was 1.17 μW and the tunable bandwidth was up to 100 GHz.Futhermore,to be more miniaturized,one commercial 1.5-V battery replaced the current source as bias,making it operate like a flashlight.This convenient and economical setup may accelerate the applications and promotions of THz science and technology.4.Power-adjustable THz Source.Vanadium dioxide(VO2)is a kind of metal oxide with metal-insulator transition(MIT),which is able to modulate the transmission of electromagnetic waves.A power-adjustable THz source,combining a high-Tc superconducting BSCCO THz emitter with a VO2 tunable attenuator,has been proposed for the first time,remaining frequencies and temperatures unchanged.At 20 and 25 K,the maximum attenuations were about-5.6 and-4.3 dB respectively.Such a THz radiating setup can further expand researches and applications of THz science and technology,and establish a good exanple of multidisciplinarity.In addition,thermal and electrical triggering MITs in VO2 were observed,of which the latter was described by electron correlation effects.By means of experiments,it was proved that the electrical triggering MIT was a result of coaction of heat and electric field. |
