Tri-wavelength broadband antireflective coating built from refractive index controlled MgF2 films

Regulation of the refractive index over a wide range is very important in the realization of tri-wavelength antireflective (AR) coating in high power laser systems, but many regulation approaches are too complex or violent to satisfy the practical requirements. Here, a simple, template-free sol-gel route was proposed to regulate the refractive index of MgF 2 film by heat treating MgF 2 sol and hence to control the self-assembly process of colloidal MgF 2 nanocrystals. In this self-assembly process, the originally packed nanocrystals gradually evolved into bigger hollow vesicles, which reduced the refractive index of the MgF 2 film from 1.38 to 1.2. When the refractive indices of the bottom and top layers were set as 1.34 and 1.2, the tri-wavelength broadband AR coating was finally realized on a quartz substrate, with the transmittance of 99.54%, 98.65% and 98.58% at 351 nm, 527 nm and 1053 nm, respectively. Tri-wavelength broadband AR coating derived from refractive index controlled MgF 2 films was realized through controlling the self-assembly process of MgF 2 nanocrystals.