Investigations of MgF_2 Optical Thin Films Prepared from Autoclaved Sol

摘要

MgF_2 thin films with ultra low refractive indices were obtained by sol-gel method using sols prepared from magnesium acetate and hydrofluoric acid.The sols were autoclaved in a Teflon cell at 100-180degC for 24 h and then coated on SiO_2 glass or CaF_2 crystal substrates by spin coating.Subsequently,the samples were heat treated at 150degC for 1 h.The optical properties of the thin films,such as refractive index and transmittance,were investigated in the UV region,especially in the deep UV (DUV,below 250 nm) region.Though the coatings consist of single layers,both samples exhibited high transmittance.In addition,they exhibit such antireflection effect over a very wide range of wavelength.Such a good antireflection effect was produced only by low refractive indices.It has also been confirmed that,even in the range of vacuum UV (VUV,200-150 nm),CaF_2 samples with antireflection coatings could keep such a good antireflection effect.