Applications of optical pump-THz probe spectroscopy on various physical systems

• Main Author: 林有��
• Other Authors: Prof. Sheng-Fu Horng
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/52232735842581911112

碩士 === 國立清華大學 === 電子工程研究所 === 92 === For the previous work of Terahertz Time Domain Spectroscopy (THz-TDS) in our group, we have taken the advantages of time resolved property to investigate ultrafast phenomenon in semiconductor which is pumped by optical excitation. For the focused optical power on semiconductor, the extreme high power density would form the surface plasma state. In this thesis, it would be introduced the interactions between plasma and THz wave. For this discussion, we choose SI-GaAs and InP as the experimental samples, comparing the difference of THz spectrum with and without optical pumping. The optical pumping is pulsed laser with 800nm wavelength and average power below 0.3W. It is 240ps that THz probed arrived after optical excitation, we measure the quasi-static optical pumped phenomenon. Also, we investigate the influence of Au nano-particles thin film spin on semiconductor surface. We find that THz wave will be absorbed by the optical pumped surface plasma, but absorption does not proportional to optical pumping power. It has been investigated that this phenomenon may be caused by semiconductor surface traps and defects. For Au nano-particles spin on semiconductor surface, without optical pump, there is no particular influence. With 800nm pulsed optical pump, we find THz absorption is linearly proportional to optical pumping, that is because Au nano-particles change the semiconductor surface state. In addition to that, we used the phase and amplitude from Fourier transform spectrum to extract the index refraction and absorption coefficient. Classical Drude is used to do theoretical calculation and fit our experimental result, then we can get the corresponding plasma frequency and collision rate. Finally, we check the THz spectrum for anti-ferromagnetic material MnTe under different temperature, for this work, we try to extract the relation of temperature and ferromagnetic properties.