Relationship between gradient of antireflection film and laser induced damage threshold

Optical antireflection film is an important part of laser systems, and it is also most likely to be destroyed under laser irradiation. How to improve the laser induced damage threshold of antireflection film is one of the research hotspots. The relationship between different gradient antireflection films and laser induced damage threshold were studied without changing the target transmission and the total optical thickness of the films. Firstly, a hybrid inhomogeneous film was designed by MATLAB with hybrid design method, namely G/H₁→H/L/A. Secondly, the inhomogeneous film was graded into different layers by the inhomogeneous film grading equivalent method. And using the plasma enhanced chemical vapor deposition (PECVD) technology, different inhomogeneous antireflection film structures (multilayer graded-index antireflection film structures and corresponding inhomogeneous film structures) satisfying optical performance indicators were deposited on K9 glass. Finally, the laser induced damage threshold (LIDT) of the films were measured. The results show that, without changing the target transmission and the total optical thickness of the films, the inhomogeneous antireflection film has a significant improvement in the LIDT compared to the conventional antireflection film. When the number of gradient layers increases, the LIDT of the inhomogeneous film structures decreases. And for the inhomogeneous films of the same layer, the LIDT of the sample prepared by the slope method is better than that of the sample prepared by the gradient.