Gain Characteristics Of Surface Plasmons In Optically Or Electrically Pumped Graphene Structures

New material graphene is a unitary layer carbon atoms tightly stacked into a twodimensional beehive monocrystal structure. It has novel photoelectrical and mechanical qualities. Due to carriers’ relaxation and gapless energy spectrum characteristics, population inversion occurs in strong pumped graphene, which can lead to electromagnetic wave emitted by interband recombination process of carriers in the range of terahertz(THz) frequencies. It’s an important way to produce and amplify THz wave. In view of the theory of optically and electrically pumped grapheme structures, we studied the parameters optimization of gain of THz wave and surface plasmons(SPs) amplification in THz range.The first chapter induces the concepts of THz and graphene,their characteristics, development, application and preparation methods of graphene metarial, describes the current research status of amplification of THz wave and plasmon based on graphene at internal and abroad. It gives background and reasons for the selected topic.The second chapter bases on the theory of optically and electrically pumped graphene, and studies parameters optimization of negative dynamic conductivity in THz range. The gain of THz wave can be larger in electrically pumped graphene. In addition, chosing proper amout of graphene layers and long relaxation time can get large THz gain at low temperature.The third chapter bases on optically pumped multiple graphene layers(MGL) structures, discusses parameters dependences on the real part of propagation index and absorption coefficient, and compares the peeling-graphene-structure and the graphene structures having a high conducting bottom graphene layer. SPs of the peeling-graphene-structure can get higher efficient amplification. Meanwhile, the structures having properly numbers of graphene layers can get larger gain than the single graphene layer(SGL) structure at low temperature.The forth chapter bases on electrically pumped SGL structures with split gates, calculates functions of propagation index and the imaginary component of dynamic conductivity, simulates the SPs absorption coefficient and the real part of the propagation index, and compares the SPs absorption coefficient and the real part of propagation index in optically pumped graphene and electrically pumped graphene. The SPs gain in electrically pumped graphene with higher bias voltage is larger than that in optically pumped graphene. A large SPs gain can be achieved by lowering the effective temperature, choosing graphene layers with a longer momentum relaxation time, applying a low gate voltage and high bias voltage.The fifth chapter bases on electrically pumped MGL structures, calculates its conductivity, and simulates SPs coefficient of absorption numerically. The largest SPs gain can be enhanced by lowing temperature, applying bias voltage V ?100me V, and choosing graphene with proper amout of graphene layers and relaxation time t ?10 ps.