| The all solid-state Q-switched lasers, which composed by adding the Q-switching components to the solid-state lasers, are of great interest because of their wide applications with the advantages of all solid state, small volume and high pump efficiency. For the Q-switched lasers, it is essential to optimize the performance of Q-switching components to achieve many of the desired properties. The semiconductor saturable absorbers has been paid much attention on as passively Q-switching components for the advantages of small volume, simple structure, convenient utilization and inexpensive price.In this paper, the output energy and the pulse width of the diode-pumped passively Q-switched laser with a novel central semiconductor saturable absorbption mirror(C-SESAM) are optimized by the rate equation theory; and the electronic structures and the elastic properties of GaAs and InGaAs saturable absorbers are calculated by the molecular simulation technology.The main study contents and the main innovations of this dissertation include:a) According to the Q-switching mechanism of the central semiconductor saturable absorbption mirror(C-SESAM), and by considering the saturable absorption effect of GaAs and InGaAs saturable absorbers simultaneously, the normalized rate equations of the passively Q-switched laser with a C-SESAM are introduced under the Gaussian distribution to describe the laser pulses'output characteristics. The key parameters of an optimally passively Q-switched laser are determined and a group of general curves are generated based on the optimizing the pulse energy for the first time.b) The change of atom configuration in GaAs, caused by intrinsic point defects (Ga and As vacancies, Ga and As antisites, Ga and As interstitials), are calculated firstly by plane wave pseudopotential method with the generalized gradient approximation in the frame of density functional theory, and the most stable structure are obtained. Then the formation energy of each kind of native defect is calculated, by which the possibilities of the six kinds of point defects to be formed during crystal growth are analyzed. The defect energy levels corresponding to every kind of native point defect and their electron occupancy are analyzed from the aspect of density of states. Finally, the elastic constants of GaAs saturable absorber with native point defects are calculated, and the impacts on the elastic properties brought by native point defects are studied. The values of defect energy levels obtained will be helpful in ascertaining the mechanism of the EL2 deep level in the GaAs saturable absorber, and the analysis of the elastic properties of GaAs crystal with native point defects will be helpful in guiding the application of GaAs crystal as a saturable absorber in passively Q-switched lasers.c) The electronic structure and elastic properties of the InGaAs crystal with different doping concentration of Indium are studied by the plane wave pseudopotential method based on density functional theory (DFT) with Cambridge serial total energy package (CASTEP) program. The density of states and the elastic constants of the InGaAs crystal with different doping concentration of Indium are obtained. The elastic modulus are also calculated from the theoretical elastic constants by Voigt-Reuss-Hill averaging scheme. The band gaps of the InGaAs crystal decrease monotonically with increasing Indium concentration. And the elastic constants with the symmetry of cubic crystal system decrease monotonically with increasing Indium concentration, too. With increasing Indium concentration, the tangential deformation of the super-cells is more prone to occur. And the brittleness of the InGaAs crystal decreases and the ductility of the InGaAs crystal increases monotonically. The values of the elastic constants obtained will be helpful in solving the problem of lattice mismatch between InGaAs and GaAs saturbale absorbers and guiding the application of InGaAs/GaAs as a saturable absorber in passively Q-switched laser. |
PDF Full Text Request