Research On Laser Pretreatment And Mechanisms Of HfO₂Optical Thin Film

Optical films are an integral part of laser systems, but film itself is easily fragile and prone to damage under high power laser. It is extremely necessary to improve the LIDT of film in order to solve the problem. Currently, the laser pretreatment which can improve the LIDT of film is a research hotspot. The laser pretreatment mechanisms of films prepared under different conditions are not the same, research on laser pretreatment mechanisms is significant for improvement of film LIDT. HfO2materiel has many features that high melting point, high hardness, good thermal and chemical stability, wide transparency range, it is important that HfO2materiel has higher laser damage threshold in the high refractive index materials. So, HfO2film was chosen as study object on the laser pretreatment mechanism in this article.In this paper, the electron beam thermal evaporation was used to prepare HfO2single layer film which was processed with10%,30%,50%and70%of film LIDT in1-on-1. The laser pretreatment mechanisms were researched through the comparison of surface micro morphology, microstructure. optical properties and LIDT of film before and after the laser pretreatment. Based on the mechanism of impurity removal, firstly, three irradiation ways were used to process film and the LIDT of film were tested. Secondly, single layer film was prepared on the substrate cleaned and its LIDT were tested. The results show that:1. In1-on-1laser pretreatment method, the film pretreated was compared with film without pretreatment, the number of the impurities and the damage spots of film pretreated are reduced, what’s more, the LIDT of film is increased, which indicate that the laser pretreatment method can effectively remove the impurities in the film and improve the LIDT of film. 2. In1-on-1laser pretreatment method, the film pretreated was compared with film without pretreatment, the surface roughness of films pretreated is decreased, the refractive index is increased, the extinction coefficient is reduced, the transmittance is slightly drifted towards long wavelength, the diameter and depth of damage spots are reduced, which indicate that the laser pretreatment can smooth, tamp and reinforce film.3. The Film pretreated by30%of LIDT was compared with film pretreated by other energy, the decline of the roughness is the largest, the increase of the LIDT are the maximum, the drift amplitude of the transmittance curve is the maximum, the number of damage spot of film is the least, the diameter and the depth of damage spot are the smallest, which show that the laser pretreatment of30%energy order has the most obvious effect on the properties of film.4. By the1-on-1, s-on-1and n-on-1laser pretreatment, the LIDT of films are26.86J/cm2,28.03J/cm2,28.26J/cm2and were compared with the LIDT of film without pretreatment, LIDT are respectively increased by46%,53%and54%, which show that those three ways based on the mechanism of impurity removal can all strongly remove the impurities in the film, and the n-on-1laser pretreatment method has the strongest clearance ability, moreover the laser pretreatment can effectively improve the LIDT of film.5. The LIDT of film prepared by using composite cleaning process is22.10J/cm and was compared with the LIDT of film that is not processed by composite cleaning method, the LIDT is increased by22%.