Laser-Diode Pumped Monolithic Nd～(3+):YAG Laser Passively Q-Switched By The Saturable Absorber Cr～(4+):YAG

Diode-pumped passively Q-Switched monolithic microchip laser is a full solid state lasers, which could realize the output laser on the level of the extremely short pico-nanosecond pulse width, high peak power up to KW, and pulse repetition rate of the magnitude of KHz. This new class of lasers could be used in many applications as a pulsed light source where the size are limited. The aim of the present report is to design and optimize the system of this kind of new microchip laser, and to complete this aim the saturable absorber Cr4~:YAG substrated on YAG chip are prepared and the corresponding spectra are analyzed. And the output performances of the microchip laser are also worked out based on the numerical calculation of the Q-switching rate equation. Firstly, with the codoped CaO and Cr203 in YAG recipe, the saturable absorber Cr4~:YAG thin film (thickness=75.7um) substrated on the undoped YAG was successfully grown by LPE(liquid phase epitaxy). The results from the absorption spectra analysis of the Cr4~:YAG show that the main features in visible and near- infrared range are the same as these grown by Czochralski, nevertheless, there is a weak absorption band centered around X~75Onm,which is first reported in the YAG lattice field. This observed weak band were interpreted as the arising from tetrahedrally coordinated Cr5~, and proposed to assign to the electric-dipole allowed 2B2(2E)=~2B1(2T2) transition. The transmission variation AT (i.e., the difference between saturated and unsaturated transmission at I .064um of the Cr4~:YAG film) of the Cr4~:YAG epilayer have been tested out, the results is beween 1 2.2?8.8%. the Cr4~ concentration in Cr4~:YAG epilayer are expected above 1.98 X 10+13 ions/cm3, which is at least of one order of magnitude greater than the Cr4~ concentration in the Czochralski Cr4~:YAG crystals. Secondly,based on the model of [Cr04]4 cluster (D2d) and without the potential IH of external crystal lattice field, the CI-Single(Configuration Interaction of Singly Substitution) molecular orbital theoretical method of ab initio quantum mechanical method and basis sets 6-31 ++g* * for Cr and 0 atoms and ligand field theory have been used to calculate the energy level structures of Cr4~ in Cr4~:YAG). Nearly 20 low-lying excited states energy levels are worked out. The results show that the 5- calculation optical transitions in the visible and near-infrared range are in good agreement with the corresponding experimental absorption spectra. The life time of some excited states, and the electric and magnetic dipole moments for the corresponding transitions are also worked out by the molecular orbital theoretical calculations. Finally, through the full numerical calculation on the passively Q-switched rate equations including the effects of the fine energy levels structure of the gain media Nd3~:YAG and saturable absorber Cr4~:YAG in the monolithic diode-pumped microchip laser grown by liquid phase epitaxy on the Nd3~:YAG substrate, the relation of the output performance of the Q-switched laser with the pumping rate, of fiber-coupled diode laser, length of the resonator, reflectivity of the output mirror and the product between the Cr4~ concentration and length of the saturable absorber have been presented out. The results are of importance to the optimization of the design of the fiber-coupl...