Paper and Progress Report Artoni Kevin R. Ang July 1, 2009
Progress Report • Changed substrate holder • Added a new pair of electrodes and boat holder
Progress Report • Coated Cr-Cu-Cr mirror (4 designs) • Measured transmission of the Cr-Cu-Cr coatings using the Ocean Optics Spectrophotometer
Things to do: • Get micrograph of Cr-Cu-Cr mirrors • Schedule FTIR analysis for mirrors • Perform adhesion tests on Cr-Cu-Cr mirrors • Finalize anti-reflection design • Modify evaporation set-up to allow evaporation of new film materials.
Paper Report • Multilayer antireflection coatings for the visible and near-infrared regions • H. Ganesha Shanbhogue, C. L. Nagendra, M. N. Annapurna, S. Ajith Kumar, and G. K. M. Thutupalli • 1 September 1997 Vol. 36, No. 25 APPLIED OPTICS
Introduction • Current research involves improving: • optical performance over a wider spectral range • transmission efficiency • spectral coverage • angle-of-incidence stability • durability • efficiency (residual reflection loss)
Introduction • Problems: • AR coatings on a variety of glass substrates • Different indices, chemical compositions, hardness, environmental stability, etc. • Different uses • Residual reflection loss, transmission efficiency, angle of incidence stablity, etc.
Optical material combinations • MgF2 and medium or high index materials • MgF2 and ZrTi04 and Zr02 (sub2) • MgF2 and Si02, Al2O3, oxides of tantalum, titanium zirconium, and niobium • Sub1 and Ta2O5+SiO2,TiO2+Ta2O5 and SiO2+TiO2
Optical Material Preparation and Characterization • Sub2 • E-beam evaporation • Base pressure: 10-5 mbar • Added high purity dry oxygen: 10-4 mbar
Optical Material Preparation and Characterization • Hitachi double-beam spectrophotometer, Model U 3400
Optical Material Preparation and Characterization • MgF2 • Same fabrication set-up • Substrate temperature: 200°C • 2x10-5 mbar
Optical Material Preparation and Characterization • Tpeak: transmission peak • A: Cauchy dispersion constant
Optical Material Preparation and Characterization • MgF2 index of 1.35±0.01 • Literature value of 1.38-1.37
Design optimization • Seven layer system of MgF2 and Sub2 coatings in alternate layers • Wideband (WB) AR coatings • Limited band (LB) AR coatings • OPTOSOFT- software to optimize design
Experimental investigation • Leybold Hereaus vacuum evaporation plant Model 560L • Optically polished and cleaned glass substrates • Substrate temperature: 200 ±5° • Rate: 0.3-0.5 nm/s for MgF2 and 0.05-0.1 nm/s for Sub2
Experimental investigation • Optical transmittance and reflectance • Durability tests • High-temp. humidity • Thermal shock/ cycling • hot-cold soak.
Conclusions • IRL R*, Rav, ripple Rmax are interlinked to spectral bandwidth. The higher the bandwidth, the higher R*/Rav and the Rmax. 2.Higher-ripple designs can also have global optical properties (R*/Rav and Tav) that are comparable with those of lower-ripple designs but they have higher spectral instability.
Conclusions 3. Sub2 high-index material in combination withMgF2 allows the production of efficient AR coatings with the electron-beam evaporation technique, in terms of both optical properties and durability of the coatings.