Study Of Filter Film Technology Used In Laser(1.064μm)/Infrared (3～5μm) Optical System

Because of good performance in near middle infrared waveband with high transmittance, as well as optical, mechanical, thermal and shock resistance property in normal temperature, sapphire is the preferred selection of material for laser infrared optical system. The lack of material processing technology makes transmittance of sapphire less than its theoretical value. Moreover, the poor strength at high temperature limits other performance of the sapphire. Depositing AR coating and protecting coating on the sapphire dome or window is an effective way to improve both optical properties and strength at a high temperature.The laser infrared optical system always requires a high transmittance at1.064μm and3-5μn band. Although DLC, SiC, and Si3N4possess high hardness and good transparency at3-5μm waveband, the absorption there at1.064μm stays in an unacceptable level, so they cannot be the protecting film of the laser infrared system. Amorphous Al2O3have been chosen as the protecting film considering the good mechanical properties and high transmittance at1.064μm and3-5μm waveband.Plasma enhanced chemical vapor deposition (PECVD) method, which has been used for deposition of AR and protecting film, choosing SiO2and TiO2as the low and high refractive index material respectively, and Al2O3as the external protection material, the preparation processing and performance of the film has been studied. The specific contents are as follows:According to the characteristics of the laser infrared optical system,AR and protecting film have been deposited with assistance of plasma enhanced chemical vapor deposition (PECVD) technology on the sapphire substrate, the requirements of the laser infrared optical system has been met.The SiO2and TiO2thin films has been fabricated on the substrate of sapphire using PECVD method. The effection of dominating processing on deposition rate, adhesion, and residual stress has been revealed. With simulation of the electrical field by Femm software, and the aid of taguchi method, the uniformity of the film thickness on Dome has been greatly improved. The uniformity of film thickness is less than8%, the requirements of film uniformity on laser infrared optical system has been achieved.The Al2O3protective film have been prepared using PECVD method, and choosing ATSB as the precursor and Ar as the carrier gas,revealing the effect of the main processing parameters on deposition rate, hardness, adhesion, residual and stress. According to the optical dispersion data of SiO2, TiO2, and Al2O3, the AR protection film system have been designed to increase the transmittance of the whole dome by8%, which made it meet the using requirements successfully.The hardness test and the bending strength test on coated and uncoated substrate have all been made to show that the average flexural strength of coated substrate, which is better than the uncoated sample. The average flexural strength of coated substrate turns out to be1.27times stronger than the uncoated sapphire at600℃. It has been proved that, Coating can improve the surface quality of sapphire,and then enhanced the strength at high temperature.