Magnesium fluoride (MgF2) is a widely used optical window material in lasers. Laser-induced damage in MgF2 materials involves complex thermal-mechanical coupling issues. With the rapid development of high-power fiber laser technologies and application of optoelectronic countermeasures, it is necessary to investigate the damage mechanism of 1.06 μm high-power continuous-wave laser on MgF2 optical windows to clarify the laser damage threshold and factors influencing laser-irradiated MgF2 window mirrors. Therefore, based on the theory of heat conduction and elastic mechanics, a simulation study was conducted using the finite element method. First, based on the thermo-mechanical theory, established a thermo-mechanical damage model for a laser-irradiated MgF2 crystal. Second, we calculated the temperature, stress, and strain fields of single-crystal MgF2 material under the action of a 100 W / cm2 laser. When the laser was irradiated for 4.921 s, thermal stress-induced burst damage was observed, but no melting damage occurred. Finally, the impact of parameters such as the laser power density, spot size, and laser action time on the damage effect was discussed using the parametric scanning method. The calculation results showed that the aforementioned factors significantly impact the damaging effect. Moreover, under the same laser parameters, material burst due to thermal stress is expected to precede the melt damage.
An experimental setup of mid-infrared Fe:ZnSe laser operating at room temperature has been established, which was end-pumped by a non-chain pulsed HF laser. The temperature has significant influence on the level lifetime of Fe:ZnSe laser. As the crystal temperature changes from 85 to 295 K, the level lifetime of Fe ions changes from 57 to 0.35 μs, it is important for matching the pump pulse width and the level lifetime. Electronic excitation HF laser with short pulsed width is a good pump source for Fe2+:ZnSe laser at room temperature. For the Fe2+:ZnSe crystal with size of 20×20mm, when the pumping spot diameters is lower than 9.2mm, the phenomenon of transversal parasitic oscillation could been suppressed effectively. At room temperature, the output energy of Fe2+:ZnSe reaches 294mJ, the slope efficiency is about 36%, and the optical to optical efficiency respecting to the pump energy is 34%.
Crystal thermal characteristic is a key factor to affect output laser property. In some applications, the facets of crystal will be contaminated by dust in the air, which will enhance the heat absorption of laser and cause local thermal unbalance. Therefore a novel crystal heat dissipation method is proposed in this paper. Crystal is mounted in a specially designed heat sink, heat conducts between the contacting surfaces of crystal and heat sink. Pump incident laser irradiates from the end facet of crystal. The end facet of crystal is cooling by convection heat transfer with flowing protect gas. The experiment device is established, the pump laser is Hydrogen Fluoride laser with the wavelength of 2.8μm, pulse energy of 600mJ, and repetition rate of 50Hz. The crystal is Fe: ZnSe with the dimension of 20mm× 20mm× 6mm. The beam quality is measured in the condition with and without heat sink for comparison, the results indicate that the heat dissipation method proposed in this paper is benefit for improving the beam quality.
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