Fabrication and damage characteristics of low stress HR films for femtosecond laser system

With the development of femtosecond laser system, the laser damage threshold of optical components becomes more important. Meanwhile, in order to obtain better laser beam quality and avoid wavefront distortion caused by optical components, more stringent requirements are put forward for the surface shape of the coated surface of mirrors. HfO2-SiO2 high reflective films were fabricated by e-beam thermal evaporation method. Internal stress of the multilayer dielectrics was modulated by changing the design of films and coating process. Finally, the film with an absolute internal stress less than 100MPa was obtained. The laser damage characteristics of the films at 35fs, 1000Hz were studied, and the damage mechanism was analyzed.