CaF2 has become the most important substrate for vacuum ultraviolet (VUV) optical coatings. The popularity of CaF2 relies on its transparency range, which extends down to 120 nm. A major drawback of the material is, however, its mechanical softness. Hence careful assessment of the surface quality is necessary in order to obtain low loss components. By combining roughness data from Nomarski Microscopy and Atomic Force Microscopy (AFM) measurements with total and angle resolved scattering measurements at 157 nm scatter losses due to interface roughness as well as bulk inhomogeneities are being studied. Measured losses are furthermore compared with theoretically predicted results. Results are also presented on VUV coatings. The question of the coupling between the substrate surface finishing quality and the optical properties of the coatings is specially addressed.
We report on an arrangement that measures angle resolved scattering (ARS), total scatter (TS), transmittance (T), and reflectance (R) at 157 nm and 193 nm. The ARS set-up is based on a high precision double goniometer arrangement, which can be inserted into the measurement chamber without removing the TS set-up. The TS set-up for detection of forward scatter and backscatter with extremely low background scatter levels of 1 ppm consists of an excimer laser, a Coblentz sphere with detection system, and a beam preparation path. The sphere and preparation path are housed in vacuum chambers allowing operation in vacuum or purge gas. The measurement options altogether constitute a multifunctional system: VULSTAR (VUVLight Scatter, Transmittance, and Reflectance). We present total scatter measurements on deep ultraviolet (DUV) and vacuum ultraviolet (VUV) substrates and optical components with antireflective (AR) and highly reflective (HR) coatings, angle resolved measurements on optical components and R and T measurements on substrates for VUV optical coatings.
We have developed a system that measures total and angle resolved light scattering, reflectance and transmittance at 193 nm and 157 nm. This system allows the investigation of substrates and coatings for vacuum-ultraviolet (VUV) components with high sensitivity, down to scattering levels of 1 ppm for total scatter measurement. The dynamic range of the angle resolved scatter measurement set-up exceeds 9 orders of magnitude. Methods for evaluating the quality of CaF2 substrates for low loss optical components for 157 nm are presented. By using roughness data from Atomic Force Microscopy (AFM) measurements combined with scattering measurements surface roughness as well as inhomogeneities in the bulk of the material can be studied. Results are also presented of anti-reflective (AR) and highly reflective (HR) multiplayer coatings on CaF2.
Methods for evaluating the quality of CaF2 substrates for vacuum ultraviolet (VUV) low loss optical components are presented. Today superpolished CaF2 is available. However, major differences might still occur between batches and careful control is therefore necessary. By using roughness data from AFM measurements combined with total scattering measurements at 193 nm and 157 nm surface roughness as well as inhomogeneities in the bulk of the material can be studied. Results are also presented of anti-reflective (AR) and highly reflective (HR) multilayer coatings on CaF2 where reduced total backscatter scattering was found for the AR-coating as compared to the substrate.
Thin films were made by spinning a dispersion of tin-doped indium-oxide particles, having an average diameter of 14 nm, onto glass substrates. As-deposited thin films displayed a resistivity (rho) of 0.3 (Omega) m and some optical absorption. Annealing in vacuum at 200 to 400 degree(s)C for 2 h, and subsequently in air at 500 degree(s)C for 2 h, produced films with (rho) equals10--3 (Omega) m and a visible transmittance exceeding 90 %. Leaving out the vacuum treatment yielded higher resistivity.