Optic Properties Of Graphene And Its Application In Laser

Graphene has been proven to be a typical semi-metal material of the zero bandgap, the valence band and the conduction band perfect symmetry intersect at theFermi level（K and K’ points）. The K and K’ points call the Dirac point. The electronicband relationship near the Dirac point is Dirac cone. Graphene has a wide-bandabsorption and zero band gap structure, so that it can be used as an effective saturableabsorber for the output of an ultrashort pulse、 ultra-high energy and high repetitionrate laser.The graphene, as the form of dispersion liquid, was prepared by reduction ofgraphite oxide. Through the oxidation-reduction chemical reaction of the raw materialof the graphite powder, with NMP as the solvent, combined with the pulverizationprocess and the centrifugation process, precise and reasonable control pulverizationtime and centrifugation speed, the graphene dispersion liquid, meeting the testrequirements, was prepared. With the UV-vis, the samples’ absorbance of400nm-1100nm spectrum were measured. Measuring the samples of the1064nm and1342nm laser absorption rate and the relationship of the incident laser power, it’sconfirmed that the graphene dispersion liquid having a saturable absorptioncharacteristic.The electronic band structure of single-layer and multilayer graphene wasstudied using the tight-binding approximation, and the Dirac fermions tunnelingeffect was studied, too.The graphene dispersion liquid was droped into the quartz cuvettes of differentlength of the light through. As a saturable absorber, it was inserted into the resonatorof LD-pumped Nd: YVO₄laser. The Q-switched operation of1064nm and1342nmlaser are achieved and their laser pulses are6.06ns and7.53ns, respectively.Combined with the nonlinear absorption characteristics, the operation mechanism ofthe passively Q-switched was analysed. Selecting the sample with the most excellentsaturable absorption characteristics, a flashlamp-pumped Nd:YAG laser mode-locked operation was achieved, and the operation mechanism of the mode-locked wasdiscussed, too.Using overlap two collinear branch cavity constitute a three-mirror compoundcavity, by setting the appropriate cavity length and the appropriate combination of theoutput mirror, to meet the condition of a equal oscillaion threshold between the1064nm and1342nm lasers, the LD-pumped Nd:YVO₄laser dual-wavelength laserwas obtained. And inserting the graphene as a saturable absorber,1064nm and1342nm dual-wavelength Q-switched operation was achieved.