It is well known that the optical property of an optical thin film can be influenced by even small inhomogeneity of refractive index (RI). In order to investigate the RI inhomogeneity of LaF3 single layer in deep ultraviolet (DUV) range, single-layer LaF3 samples deposited on fused silica and CaF2 substrates are prepared by resistive heating evaporation at different deposition temperatures. The reflectance and transmittance spectra of LaF3 film samples are measured with a spectrophotometer, and
