Rresearch Of The Gradient Refractive Index Thin Film For Laser Protection

Minus filters for laser protection need filter out some specific wavelengths in the wide high transmission wave band, which is mainly used to protect the photodetectors and soldiers from laser damage. In recent years, with the development of laser technology, the application of laser weapons in the military is uesd more and more widely, and the laser protection technology has become one of the focal point of research. Gradient refractive index film is a kind of graded-index films. It has many advantages compared to the traditional optical thin films. How to acquire a given refractive index between the high and low refractive indexes has become a hot and difficult point in the field of optical thin film technology now.The materials (SiO2 and TiO2) are selected to explore the feasible way to get the mixed refractive index films by single source mix evaporation and double source electron beam co-evaporation, respectively. The experimental results show that the ideal mixed refractive index films can not be achieved in the current device conditions because of the difference of evaporation properties of SiO2 and TiO2. The uniform mixed refractive index film can be obtained by the double source electron beam co-evaporation only when the deposition rate of SiO2 and TiO2 both are strictly controled and deposited stably. The result shows that when SiO2 and TiO2 are deposited by the deposition rate ratio (1:2), the measured refractive index value at 550nm (2.029) is close to the calculated value (2.056)Several methods are used to design the minus filter, including the traditional irregular system of two materials and the gradient system of three materials. Three types of gradient layer systems are given using the different layer system structure. The final layer syetem is determined as S|0.4 (LMHML) 14|Air by comparation and error analysis.The minus filter which meets the technical requirements is obtained by adjusting the preparation parameter according to simulating results. The reflectance of this minus filter is greater than 99.99% at 1315nm.