Abstract
In this thesis, we use optical-pump THz-probe spectroscopy to measure the ultrafast relaxation dynamics of quasi-particle in the misoriented bilayer graphene, which was fabricated by chemical vapor deposition (CVD), and then we use liquid gate to change the Fermi level of the sample for observing carrier relaxation dynamic. In early, the research about the relaxation dynamics on graphene which grown on SiC substrate was published, and it showed the negative pump induced differential transmission (PIDT), that is, a transient positive conductivity after photoexcitation. In 2013-2014, there were the different results on CVD monolayer graphene which showed the positive PIDT, and there are two kind of opinions when the Fermi level near the Dirac point. First showed the PIDT will change sign from positive to negative when near the Dirac point. Second showed the PIDT will always positive in all Fermi level and the signal will vanish when near the Dirac point, finally, the behavior of misoriented bilayer graphene is quasi-similar with the second one. Our sample differs from monolayer graphene. Electrons can transmit between two layers, and misoriented bilayer graphene have different optical phonon dispersion relation by Raman spectroscopy. However, this different is too small to have a significant impact on the carrier relaxation dynamic. The feature of response is similar to that of monolayer, therefore, we explain our experiment results by using the analysis method in monolayer graphene.