Lijun Qi

Modeling of end-pumped Yb:YAG thin-disk lasers with nonuniform temperature distribution

A plane wave model with nonuniform temperature distribution in the thin-disk crystal is developed to describe the dynamic behavior of an end-pumped Yb:YAG thin-disk laser. A set of couple-rate equations and 2D stationary heat-conduction equations are derived. The stable temperature distribution in the disk crystal is calculated using a numerical iterative method. The analytic expression is capable of dealing with more practical laser systems than previous works on this subject as it allows for nonuniform temperature distribution in the disk crystal. Based on these results, we examined laser output intensity as a function of pump intensity, dopant concentration, resonator coupler reflectivity, crystal thickness and temperature of cooling liquid.

Amplified spontaneous emission model of thin disk laser with nonuniform temperature distribution

The amplified spontaneous emission (ASE) effect is a major factor affecting large size, high gain Yb:YAG thin disk lasers. In this paper, a model combining the rate equations including an ASE effect term and nonuniform temperature distribution in a thin disk crystal is presented. A numerical iterative method is used to analyze the dynamic behavior, the space distribution of ASE effect, and the optimum coupler reflectivity of the thin disk laser. It is shown that the temperature distribution and the size of the pump region are the main factors to influence the ASE effect and ultimately affect the output power and threshold of the laser system. In order to decrease the ASE effect, the coupler reflectivity can be adjusted to control the gain coefficient to increase output power.

Deicing with Nd:YAG and CO 2 lasers

A model of deicing with Nd:YAG and CO2 lasers for simulation using ANSYS software is presented. Experiments with a 300-W, 1-ms, 60-Hz Nd:YAG laser and a 500- to 2000-W cw CO2 laser are reported. The Nd:YAG laser is considered as a volume thermal source, and the CO2 laser as a plane thermal source. The model and the simulation results can describe both Nd:YAG and CO2 laser deicing well. The results of the simulation and experiments suggest that the melting rates for the two lasersarealmostequalatthesamelaserpowerdensity.Soarethemelting efficiencies. The hard and transparent ice irradiated by the Nd:YAG laser becomes opaque and loose, because the thermal stress is distributed in the body of the ice, while the ice irradiated by the CO2 laser is still transparent and hard, because thermal stress hardly occurs. So the laser with characteristics of high output power and large ice absorbing length can be selected for the power line laser deicing system, and Nd:YAG laser is more appropriate for power-line deicing than CO2 laser. C 2010 Society of

Influence of beam spatial distribution on the laser damage of optical material

Based on the theoretical model of uniform pulsed laser beam irradiating on the optical material, the stress distribution of the transparent material when laser with different beam spatial distribution - circle beam spot and dark-cross beam spot - irradiated to the inner of optical material was discussed. The experiment that 532nm Q-switched laser pulse was focused to the inner of silicate glass was taken, which the beam spatial distribution of the output laser was dark-cross beam spot. According to the theory, the experimental results and phenomena were analyzed and the damage micro-configurations were explained. The theory and experiment could be accordant well.

Design of homogeneous laser-line-beam generators

Abstract. We present a laser beam shaper designed to obtain a homogeneous line beam. A beam shaping system was designed based on cutting and rearranging optics, using two groups of plane parallel plates. The analysis of beam uniformity was performed by use of ray tracing simulation through ZEMAX software and experimental validation. The simulation results show that in the focal plane, a beam width of 1 mm (@95%Imax) and a uniformity of 90.2% are achieved in one direction, and a Gaussian profile with a beam width of 0.06 mm (FWHM) is achieved in the other direction.

New type of fiber mode stripper with quartz tubes

Fiber cladding mode stripper is one of key devices in high-power fiber lasers and high-power transmission fiber. We report a new kind of mode stripper using quartz tubes with etched dots on the surface. We studied the waveguide property of the mode stripper both the dots on the outer surface and on the inner surface of the tube. Then we produced some quartz tubes using green laser for the experiments, which demonstrated that the new model strippers can reduce the cladding light and improve the axial temperature distribution obviously.

Research of transparent materials bulk damage characteristics by using modulated laser pulse

The experiment is carried out with ns Q-switch 532nm laser focusing into the transparent material to research the damage characteristics. The theory models about modulated pulse series are built up. Some main parameters such as interval of modulated sub-pulse, single pulse energy, peak power, and pulse duration are studies in process of laser bulk damage in transparent material. Some useful conclusions are acquired.