The Research Of Thermal Dissipation In LD End-Pumped Nd: GdVO₄ Laser

In the process of pump wavelength transferring, part of the pump power transforms into thermal power inevitably, which will lead to the uneven spatial distribution of temperature inside the crystal, so it will arouse the thermal deformation, thermal stress and birefraction. Thermal effect of laser crystal has already become the bottleneck problem in the power scaling, Q-switch operation and frequency doubling with the rapid development of solid-state laser technology. So we discuss how to solve the thermal dissipation problem in the thesis.In the paper, modeling of temperature and thermal stress distribution in the crystal, calculation of focal length of thermal-lens and the heat load comparison among Nd:GdVO4, Nd:YVO4 and Nd:YAG were made theoretically. Meanwhile, the temperature field and thermal stress distribution in the crystal were simulated by LASCAD software. All of these provide theoretical basis for our elimination of heat. Then based on the principle of thermal conductivity and fluid mechanics, radiating mechanism of the microchannel heat-sink and the indium solder are discussed, which provides basis for the following experiment.In the experiment, by comparing the experimental results of the three different kinds of heat-sink, i.e., traditional common heat-sink, indium-wrapped microchannel heat-sink and, indium solder microchannel heat-sink, we demonstrate the good performance of our novel-designed equipment.In the experiment, we used LD end-pumped Nd:GdVO4 scheme and plano-plano cavity was employed. Under 28W pump power, we obtained 8.66W(in traditional common heat-sink) and 10.5W(in indium-wrapped microchannel heat-sink) output respectively. The optical-optical efficiency is 31% and 36%, slope efficiency is 38% and 42%, correspondingly. But when adding indium-soldered technique to microchannel heat-sink, 17.5W output was obtained under 40W incident pump power, corresponding to the optical-optical efficiency of 44% and slope efficiency of 49%. What's more, the laser output has not been saturated. Comparing the three groups of data, we can see the effect of indium-soldered microchannel heat-sink is evident. We also measured the absorbed pump power under the same thermal lens (f=350mm). When using the indium-wrapped heat-sink, the crystal can absorb 6.5W pump power; but for the indium-soldered heat-sink, the crystal can absorb 39.5W pump power, which can also demonstrate superiority of the new technique in thermal dissipation.Especially, we measured the spatial distribution of transversal mode by the laser beam analyzer. 4W and 8W fundamental mode was obtained in common heat-sink and indium-wrapped microchannel heat-sink, respectively. However, 13W fundamental mode was achieved in the indium-soldered microchannel heat-sink. This obvious progress in beam quality is pretty valuable for the research and design of CW, Q-switch and frequency doubled operation in DPSL.