Semiconductor-metal phase transition in metal oxides have attracted much attention due to their scientific significance in condensed matter physics and their possibilities in a variety of applications. During the last half century, experimental and theoretical studies on phase transition mechanism have been discussed. Vanadium dioxide (VO₂) has attracted much attention due to its phase transition properties at room temperature. The VO₂ phase transition can be triggered by a variety of excitations, such as thermal, electrical, optical, magnetic field, and strain, and because the phase transition process is reversible and its optical properties change significantly, it is widely used in optical switches, smart windows, optical storage, and laser protection. With the rapid development of femtosecond laser technology, more and more researchers are involved in the study of laser-material interactions. The control of VO₂ phase transition on ultrafast time scale using optical means will benefit its potential applications in memory devices, ultrafast optical switches and bistable optoelectronic devices.Firstly, we briefly introduce the basic properties of VO₂. The material undergoes a phase transition at room temperature (~68°C), which is reversible and non-destructive. Stimulated by external conditions, VO₂ transforms from a monoclinic semiconducting phase (P2₁/c) to a tetragonal rutile phase (P4₂/mnm) with a distortion of the lattice structure, accompanied by a change in electrical resistance of about four orders of magnitude and a consequent change in its optical properties. A common method for inducing semiconductor-metal phase transition is thermal triggering. Below the phase transition temperature, VO₂ is a semiconducting phase with a high transmittance, and when the temperature is heated above 68°C, VO₂ changes into a metallic phase with abrupt changes in its optical properties such as refractive index, transmittance, and reflectance. The phase transition can also be triggered on sub-picosecond time scales under femtosecond laser induction. Due to the extremely high response rate and significant optical property changes of laser-induced phase transition, it is important to study the laser-induced phase transition process, which will help to expand its applications in optical devices and systems.Secondly, we prepared VO₂ film using magnetron sputtering, a kind of physical vapor phase deposition which is widely used for the synthesis of VO₂ thin films due to high deposition rate, uniform film formation, high reproducibility and suitable for large area preparation. The Atomic Force Microscope (AFM) image clearly shows the surface morphology of the sample, which is found to be uniform with a high flatness, and the thickness of the sample is ~195.5 nm. The XRD pattern shows a distinct diffraction peak at 2θ = 40°, corresponding to the (001) crystal plane, indicating that the sample is a well crystallized pure phase VO₂(M). A typical thermogenic echo line is observed in the temperature-dependent transmittance curve, with the most pronounced change in transmittance near the phase change temperature, which drops sharply from ~42.1% to ~11.6%. The sample recovery temperature is at ~53 ℃ with an average hysteresis of ~15 ℃.Thirdly, the optical response of VO₂ film under femtosecond laser induction was measured using a home-built transmission and reflection I-scan experimental setup. As the incident laser intensity increases, the sample changes of transmittance and reflectance show four different stages: nonlinear absorption process, phase transition process, steady state process and damage process. At lower laser intensities (less than ~26.2 mJ/cm²), the VO₂ film maintains a high transmittance, showing a slight decrease from 43.9% to 40.3% with increasing laser intensity, while the reflectance remains essentially constant at ~6.3%, indicating that the sample does not undergo a phase change and remains in the semiconducting phase. This change is mainly attributed to the two-photon absorption process of the VO₂ semiconductor. When the laser intensity reaches ~26.2 mJ/cm², the sample transmittance suddenly decreases from ~40.2% to ~12.8%, while the reflectance sharply increases from ~6.6% to ~12.0%, which is the result of the laser-induced phase transition of VO₂ from the semiconducting phase to the metal phase. Compared with the temperature-induced transmittance change in VO₂, the same effect can be achieved by laser-induced, and it can be inferred that the phase change induced under the laser action is caused by the laser thermal effect. The steady state process is that the transmittance and reflectance remain in relative equilibrium after the sample phase changes to the metallic phase without significant change. When the laser intensity rises above ~104.4 mJ/cm², the transmittance of the sample starts to decrease, and the reflectance also starts to decrease after a slow increase, which is due to the thermal damage of the sample under the laser action. In order to further analyze the change process of optical properties of VO₂, especially the phase change mechanism of laser thermal effect, the transmittance (T) and reflectance (R) as a function of laser intensity are measured at different laser repetition frequencies, and calculated the sample absorbance (A) using the equation A = 1-R-T. The experimental results at all laser repetition frequencies show the four stages of laser-induced VO₂. With the increase of the repetition frequency, the laser-induced phase transition turn-on threshold decreases from ~45.4 mJ/cm² to ~1.3 mJ/cm² and the damage threshold decreases from ~176.8 mJ/cm² to ~5.9 mJ/cm². The laser thermal effect is enhanced and the thermal accumulation of the sample increases due to the increase of the laser repetition frequency, leading to more susceptible to phase transition and damage.Finally, a brief summary of the work is given, and we expect that this study will have a contribution to the further development of this material in the field of optics.