Study On THz Wave Generation And Coherent Control

Terahertz (THz) wave generation and coherent control are major concern of this thesis. THz wave radiation is generated through photoconductive antenna or optical rectification methods based on femtosecond laser. The active and passive control on broadband terahertz radiation are proposed and employed to modulate THz wavefront syntehsis. In the process of THz wave generation, active control is achieved by changing the wavelength and waveform of femtosecond pulse; through the interaction between THz wave and material, passive modulation of THz radiation can be realized by designing the microstructure of material. The main research work is summaried as follows:(1)The wavelegnth tunablity of THz radiation was stuided by changing the central wavelength of pump pulse based on optical rectification effect on (110)-orented ZnTe crystal; The waveforms of THz pulses generated by shaped pump femtosecond pulses were investigated. It is found that the THz radiation amplitude can be modified very limited through modifying the amplitude and phase of femtoscond pulses, and THz wave with arbitary wavefront can be achieved by laser pulse trains through waveform synthesis.(2)THz pulse can be shaped using birefringence of Lithium niobate (LN) crystal: The phase and relative amplitude of ordinary (o) light and extraordinary (e) light are controllable by changing the thickness of the crystal and the angle between the polarization of THz wave and the crystal optical axis, respectively. In addition, THz broadband antireflection coatings are designed and fabricasted in order to eliminate the unwanted THz echo pulse. We also apply the antireflection coating to the time-resolved terahertz spectroscopy: the carrier concentration of sample can be controlled by adjusting the pump power, and the internal reflection of THz wave at the interface of the sample are controllabe with optical pumping pulses. (3)The modulation of THz pulse through periodic metallic microstructures are investigated systematically, which includes one-dimensional (1D) wire grid, two-dimensional (2D) periodic metallic hole arrays and 2D periodic metallic stripe arrays. In THz regime, Rayleigh wavelength is almost overlapped with that of the classical surface plasmon, both of which dominate the transmission minimum in the subwavlength structures. Shape resonance and half-wave resonance are consistent with localized surface plasmon resonance (LSP), which plays an important role in the THz transmission enhancement. THz transmission can be controlled effectively by designing the period, dimension, and substrate of the microstructure. 1D wire grid, 2D periodic metallic hole arrays and 2D periodic metallic stripe arrays have great potential applications in THz polarizer, THz bandpass filter and THz bandstop filter, respectively.