Space Radiation Environment Tests on HOEs Geary Schwemmer* NASA GSFC Work Supported by NASA and IPO *new affiliation: Science and Engineering Services, Inc. Columbia, MD

Radiation Environment Electron (gamma) radiation Proton radiation Ultraviolet

Five-HOE ShADOE Samples 5.7 mm PPG Starphire glass 10 µm DCG hologram 10 µm Epoxy

Optical Tests Before & After Exposure Diffraction efficiency at 355 nm 0° incidence transmission at 355 nm and 2-µm wavelengths 355 nm absorption 30°

Gamma Tests Mission profile (polar orbits) Approximate dose 1-3 year, 400 km3 KRad 5-10 year, 833 km30 KRad >10 yr, >1000 km altitude or planetary 300 KRad

Gamma exposure effect on diffraction efficiency, preliminary results Radiation Dose (KRad) η 0, Pre-radiation % Diffraction Efficiency η m, Post-radiation % Diffraction Efficiency 30050±1014.5± ±1341.2± ±1536.6±8.0 Control

Gamma exposure effect on transmission at 355 nm, preliminary results Radiation Dose (KRad) T 0, Pre- radiation % Transmissio n (sum of 0+1 orders) T m2, Post- radiation % Transmissio n (sum of 0+1 orders) T m1, Post- radiation % Transmission (0°-incidence) T m3, Post- radiation % Transmission (spectro- photometer) ±  ±   ±   ± Control76.8±

Co MeV gamma ray exposures 300 KRad 30 KRad 3 KRad 0 KRad

Spectral Transmission

254 nm UV 100 nW/cm^2 for 12 min = 3.15 J/cm 2 equivalent to ~ 1 year in orbit

355 nm transmission loss vs. 254 nm exposure

Conclusions & future tests Moderate 355 nm absorption due to gamma radiation over NPOESS mission life: ~25% thru 11.4 mm of glass. Little to no hologram fading due to 254 nm or gamma radiation exposure. No degradation at 2-microns. Thinner glass will decrease absorption. Proton radiation & high intensity 355nm UV tests TBD