1ANL LAPD Meeting 10/15/09

O.H.W. SiegmundExperimental Astrophysics Group,

Space Sciences Laboratory, U. California at Berkeley

Window Transmission and Reflection Considerations

for LAPD Detectors

GALEX M31

2ANL LAPD Meeting 10/15/09

Window/Photocathode Configuration 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

ARcoating

ITOcoating

3ANL LAPD Meeting 10/15/09

Standard WindowsStandard Windows

Acceptable cutoff range

4ANL LAPD Meeting 10/15/09

Standard Night Vision WindowsStandard Night Vision Windows

A. SmithNIM 2002

5ANL LAPD Meeting 10/15/09

Borofloat 33 General Parameters

Composition Refractive index@400nm

Borofloat 33 1.47Air ~1.0Water ~1.32

6ANL LAPD Meeting 10/15/09

Transmittance and Reflectance of Borofloat 33

Transmittance is typicalfor borosilicate glasses

Standard AR coating is bad for LAPD - need re-optimization or don’t use AR coating??

7ANL LAPD Meeting 10/15/09

Graded Film, Porous Borosilicate, AR

Minot, JOSA 1977

8ANL LAPD Meeting 10/15/09

Si

Anti-Reflectance CoatingsAnti-Reflectance Coatings

9ANL LAPD Meeting 10/15/09

Anti-Reflectance CoatingsAnti-Reflectance Coatings

Sample AR optimization for NaI(Tl) scintillator

10ANL LAPD Meeting 10/15/09

Conductive Layer Properties for Windows

Braem, NIMA 2003

ITO is a good choice for the conductive underlayer

11ANL LAPD Meeting 10/15/09

Photocathode ReflectancePhotocathode ReflectanceGaAs

S20 photocathodes

Redcathode

Bluecathode

12ANL LAPD Meeting 10/15/09

Window Treatment SummaryWindow 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