Nonlinear Active-controlled Terahertz Metamaterial Device

In recent decades,terahertz(THz)science and technology has been develop ed rapidly,such as terahertz source,terahertz detector and terahertz spectroscop y system,and terahertz technology has gradually become a hot topic.The appe arance of artificial electromagnetic metamaterials promotes the development of various functional devices in terahertz region,and its application in nonlinear fi eld has been attracted more and more attention.In this thesis,the nonlinear eff ect of terahertz metamaterials is studied.The details are as follows:First,we design and build a transmission type high field terahertz time do main spectroscopy system for experimental measurement.The system uses femt osecond laser to pump nonlinear crystal LiNbO3 for the radiation of intense ter ahertz electric field,which is based on optical rectification effect.The terahertz waveform is detected by crystal ZnTe based on the electro-optic sampling coh erent detection method.The system performance is as following:The sample is located at terahertz focal point with a spot diameter of about 3 mm,and the terahertz electric field is greater than 100 kV/cm.At the same time,the THz electric field intensity and polarization can be adjusted by a pair of THz wire grid.Second,we studied the nonlinear effect of terahertz metamaterial based on vanadium dioxide(VO2)film.The terahertz metamaterial are fabricated on Al2 O3 substrates using micro/nano fabrication techniques.The cell structure is com posed of metal spit resonant square ring,and the VO2 structure is integrated at the opening ring.Then using the transmission type intense field terahertz time domain spectroscopic system,we measured and studied the nonlinear effect an d control process of the device under different intensity of incident THz electri c field.At the same time,we also studied the metamaterial excited with other external stimulus,such as temperature and femtosecond laser.We find that th e strong terahertz electric field,temperature and femtosecond laser can be used to actively control the device.Third,we studied the modulation effects of terahertz devices based on Nb5 N6 thin film materials.Firstly,using micro/nano fabrication techniques,we gro w Nb5N6 thin films on high resistivity silicon substrates,besides,periodic meta l structure of terahertz metamaterial is patterned on the thin film.Metal rings and ring holes with complementary geometric structures were selected for the u nit structure.Then,using the transmission type strong field terahertz time doma in spectroscopic system,we measured the modulation of the two kinds of sam ples under the excitation of intense THz field and femtosecond laser.The resul ts show that femtosecond laser can obviously adjust the terahertz transmission of the devices with only tens of milliwatts,which means that femtosecond lase r may change the electrical conductivity of the Nb5N6 thin films,but the terah ertz electric field with an electric field strength of about 100 kV/cm cannot sig nificantly modulate the device.