采用泵浦探测技术研究VO2薄膜相变特性

为研究纳秒激光作用下的VO₂薄膜的相变特性，采用泵浦-探测技术进行实验。首先，利用直流磁控溅射法制备VO₂薄膜，经X射线衍射（XRD）和原子力显微镜（AFM）分析表明样品质量较高。然后，测量VO₂薄膜在波长532 nm处的透过率随温度的变化情况，发现透过率随温度升高由32%上升到37%，与红外波段完全相反。在此基础上，选择1 064 nm泵浦光和532 nm探测光研究激光参数中能量密度和重频对VO₂薄膜相变特性的影响，同时结合ANSYS有限元软件对纳秒激光作用下VO₂薄膜的单脉冲温升情况进行分析。结果表明：VO₂薄膜在大于30 mJ/cm²的纳秒激光能量密度作用下，单脉冲温升可达相变温度，最小相变响应时间在14 ns左右。进一步提高纳秒激光能量密度，其相变响应时间略有增加但变化不大。在100 Hz以内改变纳秒激光重频对VO₂薄膜的相变响应基本无影响。VO₂薄膜的相变恢复时间随着纳秒激光能量密度的增大而呈自然指数增加，其变化过程与基底材料和纳秒激光参数密切相关。因此，可以通过优化VO₂薄膜基底材料参数提高其激光防护效果。

Study on Phase Transition Properties of VO2 Based on Pump-probe Technique

The phase transition properties of VO₂ thin films irradiated by nanosecond laser were researched using the pump-probe method. At first, VO₂ thin films were successfully deposited by DC magnetron sputtering method, and the samples were identified as high quality thin films by analysis of (X-ray diffraction)XRD and (Atomic force microscope)AFM. Then, the transmittance of vanadium oxide thin films at the wavelength of 532 nm with temperature change was measured. It is found that the transmittance increases from 32% to 37% with the temperature going up, which is completely opposite to the situation in infrared band. On this basis, we chose 1 064 nm pump laser and 532 nm probe laser to research the effect of nanosecond laser parameters, energy density and repeat frequency, on the phase transition properties of VO₂. In addition, the ANSYS software is also used to analyze the per pulse heating range of VO₂ thin films under nanosecond laser. The results suggest that the per pulse heating can reach the phase transition temperature of VO₂ when the nanosecond laser energy density is more than 30 mJ/cm². The response time increases slightly with the increase of the nanosecond laser energy density, and the minimum response time is around 14 ns. The repetition frequency of nanosecond laser within 100 Hz has no obvious effect on the phase transition response of VO₂ thin films. The recovery time varies with nanosecond laser energy according to natural exponential law, and it correlates closely with substrate material and nanosecond laser parameters. We can improve the laser protection effect by optimizing the substrate material parameters of VO₂ thin film.