1 ANL LAPD Meeting 10/15/09 O.H.W. Siegmund Experimental Astrophysics Group, Space Sciences Laboratory, U. California at Berkeley Window Transmission and Reflection Considerations for LAPD Detectors GALEX M31

2 ANL LAPD Meeting 10/15/09 Window/Photocathode Configuration Windows for large area devices need to perform several functions  Support vacuum  Have high transmittance/ low reflection in the required bandpass  Be a good substrate for photocathodes AR coating ITO coating

3 ANL LAPD Meeting 10/15/09 Standard Windows Acceptable cutoff range

4 ANL LAPD Meeting 10/15/09 Standard Night Vision Windows A. Smith NIM 2002

5 ANL LAPD Meeting 10/15/09 Borofloat 33 General Parameters Composition Refractive Borofloat Air~1.0 Water~1.32

6 ANL LAPD Meeting 10/15/09 Transmittance and Reflectance of Borofloat 33 Transmittance is typical for borosilicate glasses Standard AR coating is bad for LAPD - need re-optimization or don’t use AR coating??

7 ANL LAPD Meeting 10/15/09 Graded Film, Porous Borosilicate, AR Minot, JOSA 1977

8 ANL LAPD Meeting 10/15/09 Si Anti-Reflectance Coatings

9 ANL LAPD Meeting 10/15/09 Anti-Reflectance Coatings Sample AR optimization for NaI(Tl) scintillator

10 ANL LAPD Meeting 10/15/09 Conductive Layer Properties for Windows Braem, NIMA 2003 ITO is a good choice for the conductive underlayer

11 ANL LAPD Meeting 10/15/09 Photocathode Reflectance GaAs S20 photocathodes Red cathode Blue cathode

12 ANL LAPD Meeting 10/15/09 Window Treatment Summary Prospects for large windows - borofloat 33 looks good AR coatings can be very important, but may be unnecessary? Photocathode reflectivity is potentially a big issue Have to have a conductive underlayer, ITO good candidate