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Ultrafast Terahertz Spectroscopy and Nonlinear Optics of Semiconductor Nanostructures

Author: ZhaoZhenYu
Tutor: SunZhenRong
School: East China Normal University
Course: Optics
Keywords: Ultrafast THz spectroscopy Optical rectification Photoconductive antennas Quantum cascade laser Sings niobium oxide glass Nanocrystalline Nonlinear optics
CLC: TN304
Type: PhD thesis
Year: 2008
Downloads: 210
Quote: 0
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Abstract


This article discusses the two main independent use of ultrafast laser technology to study semiconductor nanostructures carrier dynamics performance: 1. Construct THz time-domain spectroscopy system and the use of this system GaAs / AlGaAs quantum cascade laser gain; 2 using Z-scan and four-wave mixing and third-order nonlinear optical properties of tellurium niobium oxide glass doped nanocrystals of silver chloride. First, we make use of the ZnTe crystal optical rectification function, initially built THz time-domain spectroscopy system. In this process, we study the optical rectification THz pulse at the same time, and other nonlinear optical processes, such as: second harmonic, two-photon absorption and free carrier carrier competitive relationship between the absorption. Tight focusing conditions, the pump laser because of the two-photon absorption and attenuation, and free-carrier absorption will lead to a decrease of the THz radiation intensity. Excitation wavelength in Asia, the THz radiation attenuation mechanism experiments revealed. Secondly, we study a new micro structure of semi-insulating GaAs photoconductive antenna THz radiation time domain and frequency domain characteristics, especially in the temperature range from 4K to 270K THz emission characteristics. Voltammetry characteristic curve shows that, under the low bias, THz emitting a linear relationship, while the high bias, THz radiation (?)-L-electron scattering saturation will occur. Under strong excitation conditions, THz emission because of the shielding of the space charge saturation occurs, the corresponding THz spectral blue shift. At low temperatures, and easier access to the shielding effect of the space charge. The THz emitter intensity at different temperatures with the the charge drift rate varies. Again, we compare the two for THz time-domain spectroscopy program, and to determine the light-guide antenna as an emission source, used to to study 2.9THz quantum cascade laser transmittance gain characteristics. We studied the gain with the injection current and temperature dependence of THz amplitude and phase relations in various spectral bands on, and thus directly derived gain value. In 2.9THz center frequency, gain 6.5cm -1 . We also note that the gain saturation and spectral narrowing. In addition, the rise in temperature leads to the attenuation of the gain. Finally, we study the non-resonant third-order nonlinear optical properties of the doping concentration of 1% silver chloride nano-crystal tellurium niobium oxide glass. Glass samples were prepared using melt quenching method and heat treatment method of crystallization, and to control the particle size of the nanocrystals and quantity by changing the heat treatment time, and combined with the absorption spectra, fluorescence spectroscopy, Raman spectroscopy and electron microscopy structure of the sample and nanocrystalline particles of characterization. The average particle size and quantity of the nanocrystals with the holding time increases, and causes the defect center of the crystal to produce more of silver chloride, which affects the lattice distortion of the interface between the nanocrystals and glass, resulting in the energy band redshift in the self-trapped exciton formation. The redshift caused localized electronic states and the two-photon absorption coefficient increases lead to optical limiting amplitude threshold decline. The fall of the transient polarization state electronic enhancements enhanced nonresonant third-order nonlinear absorption.

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CLC: > Industrial Technology > Radio electronics, telecommunications technology > Semiconductor technology > General issues > Material
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