Infrared laser protection of multi-wavelength with high optical switching efficiency VO2 film

Abstract

Vanadium dioxide (VO2) film with nanoparticles is fabricated by reactive ion beam deposition (RIBD) technology and post-annealing method on a quartz glass substrate. RIBD can enhance the damage threshold of VO2 film and reduce its scattering at insulator-state. And post-annealing can eliminate the structure defects and residual stress. VO2 film exhibits first-order and reversible metal-to-insulator (MIT) phase transition at a temperature of 68 ℃. It also exhibits photo-induced MIT, in which process a metal-like phase of monoclinic VO2 appears. With many surprising features in heat-induced and photo-induced MIT processes, VO2 film turn to satisfy all the characteristics needed for a laser protection system. The thickness of VO2 film used in these experiments and simulations is about 100 nm. The double-frequency He-Ne laser at a wavelength of 3 m is used to perform the experiment of heat-induced MIT, with a temperature controlling system. The exact optimal annealing temperature is demonstrated to be 465 ℃, as the sample annealing at this temperature shows the sharpest transition properties and unmixed VO2 phase peaks in X-ray diffraction pattern. Drude and Drude-Lorentz dispersion models are taken to analyze the dielectric constant of VO2. Then, the complex refractive index is calculated for simulation. Simulations with the TFCale software show that the transmissions at high temperature and low temperature have high contrasts in the infrared range. MIT experiments at multi-wavelength, which cover heat-induced and photo-induced MIT phase transition, are performed to investigate the applicability of VO2 film in multi-wavelength laser protection for both continuous wave and pulsed lasers Thus the excellent performance of VO2 film for laser protection is roundly verified. The laser protection experiments on silicon photocell exhibit that the VO2 film enhances the anti-jamming capability of photocell system by about 2.6 times, demonstrating the applicability of VO2 film to laser protection system. The power density of MIT transition threshold of VO2 film with a thickness of 100 nm is 4.35 W/cm2 at room temperature, which is investigated with a continuous wave laser at a wavelength of 1.08 m with a continuous tunable system. In addition, atomic force microscope is used to observe the film surfaces, which are irradiated by lasers with different power densities for different times The experimental results demonstrate that the power density damage threshold of VO2 film becomes very high (404 W/cm2). The low MIT transition threshold and high damage threshold of VO2 film further demonstrate its applicability as a key role for a laser protection system. With the high switching efficiency ratio and high damage threshold, VO2 thin film can be used in optical switch, smart windows and photoelectric device.