Study on the design and preparation technology of ultra-low profile wideband high reflection thin films

The surface shape deviation of the optical thin film element will cause the wavefront distortion of the transmitted beam in the high-precision laser system, which will seriously affect the performance of the optical equipment. The traditional surface profile deviation control technology uses double-sided coating, but it is necessary to repeatedly polish the substrate to obtain a high-precision surface profile, which will greatly increase the development cost and limit the use of this method. Based on ion beam sputtering deposition technology, a stress-deformation model was used to predict the shape change after coating, and then the coating surface of the component to be plated was pre-processed into a surface shape opposite to the deformation direction, compensating for the deformation of thin film components caused by the stress of the film after coating. Finally, an ultra-low-profile broadband high-reflection film was prepared on the pre-processed substrate to achieve reflectivity R≥99.5% and PV≤0.15λ@632.8 nm at the working wavelength of 550-750 nm. Through calibrating the mechanical parameters of thin film materials, this technology predicts the surface shape changes of any multilayer film under the same process conditions, realizes the introduction of mechanical synchronization design while designing the ultra-wide spectrums, and prepares high-quality optical films that meet the dual indicators of light and force.