The TSIS Spectral Irradiance Monitor: Prism Optical Degradation Studies

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Rosaline Phoebe Gilmore
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The TSIS Spectral Irradiance Monitor: Prism Optical Degradation Studies Lo Erik Richard, Dave Harber, Joel Rutkowski, Matt Triplett, Kasandra O Malia

1 The TSIS Spectral Irradiance Monitor: Prism Optical Degradation Studies Lo Erik Richard, Dave Harber, Joel Rutkowski, Matt Triplett, Kasandra O Malia Laboratory for Atmospheric and Space Physics (LASP) University of Colorado, Boulder, Colorado USA Special thanks to entire NIST SURF and SIRCUS Teams!! Richard - 1

Which wavelengths were responsible? Surface contamination or bulk volume effect?

2 TSIS Optical Degradation Trade Study SORCE SIM saw > 30% transmission degradation in 5 years at 220nm What caused this degradation? Which wavelengths were responsible? Surface contamination or bulk volume effect? Can we mitigate this degradation on TSIS? Can we reduce uncertainties in quantifying over mission? Richard - 2

TSIS SIM Development Approach TSIS SIM designed for long-term spectral irradiance measurements (climate research) SORCE SIM Incorporate lessons

in TSIS SIM development Reduce uncertainties in prism degradation correction to meet long-term stability requirement Ultra-clean optical environment

to meet measurement precision requirement ESR : Improved ESR thermal & electrical design Photodiodes : Larger dyn.

3 TSIS SIM Development Approach TSIS SIM designed for long-term spectral irradiance measurements (climate research) SORCE SIM Incorporate lessons learned from SORCE SIM (& other LASP programs) into TSIS SIM to meet measurement requirements for long-term JPSS SSI record Specific areas addressed in TSIS SIM development Reduce uncertainties in prism degradation correction to meet long-term stability requirement Ultra-clean optical environment to mitigate contamination Addition of 3 rd channel to reduce calibration uncertainties Improve noise characteristics of ESR and photodiode detectors to meet measurement precision requirement ESR : Improved ESR thermal & electrical design Photodiodes : Larger dyn. range integrating ADC s (21-bits) Improve absolute accuracy pre-launch calibration NIST SI-traceable Unit and Instrument level pre-launch spectral calibrations (SIMRF-SIRCUS) TSIS SIM Richard - 3

4 TSIS SIM Design Overview Féry prism spectrometer covering the full wavelength range from the UV to IR using only one optical element for spectral dispersion and image quality Richard - 4

5 Richard - 5

$Absorptance Slit diffraction Spectral Transfer function prism transmission$

6 Measurement Equation Overview ESR detected power Aperture area ESR Absorptance Slit diffraction Spectral Transfer function prism transmission Richard - 6

7 Overview of TSIS SIM CCD Assy Rotational Prism Carrier Shutter/Photodiode Assy Fery Prism Assy CCD Aperture Ch. A Aperture Ch. B Aperture Ch. C Aperture External Flex ESR Detector Assy Vacuum Door Mechanism Fine Sun Sensor Focal Plane Module Richard - 7

8 Prism Assembly Train wreck occurs here! Richard - 8

9 Material Considerations for Refractive Optics Transmission window Dispersion (dn/dλ) Absorption Leads to heating producing temperature dispersion (dn/dt) causing wavefront error Bubble & inclusion content Leads to scatter Striae layers Leads to wavefront distortion and scatter Radiation hardness Energy or power density Compaction & Color center formation Richard - 9

10 Suprasil (Fused Silica) Transmission TSIS SIM Level 1 wavelength range Fresnel Refl. Loss Suprasil 1 / 2A Suprasil 311 / 312 Suprasil 300 / 3001 Richard - 10

11 Suprasil 3001 Properties Suprasil 3001 is a high purity synthetic fused silica manufactured by flame hydrolysis of SiCl 4 High index homogeneity n/n 1 ppm over CA volume (optically isotropic 3D -material) No striations Low NIR absorption Low OH & trace impurities nm nm Richard - 11

12 Refractive Index Homogeneity < 300 ppb/cm! Richard - 12

13 Richard - 13

$range Refraction vs.$

14 Full Spatial & Spectral Transmission Mapping Prism measurement geometry is for ESR optical path Stabilized SIRCUS lasers cover nm range Refraction vs. wavelength (Suprasil 3001 fused silica) Transmission measured over 10 x 10 grid for both s and p-polarizations Richard - 14

15 Richard - 15

16 Prism Transmission 55 λ s x 100 spatial points x 2 polarizations x 4 prisms = 44,000 measurements! (5 months effort) Richard - 16

17 Suprasil 3001 Degradation Study Fabricate 6 super-polished (SR < 1 Å Rrms ) Suprasil 3001 window samples (same material and process as prisms) and 2 super polished Suprasil 312 windows Measure initial transmission from nm Expose different windows to the equivalent of a 5-year solar dose (15 orbits/day 218 days/year) at three different wavelength regions: nm : SURF facilities at 380 MeV beam energy 5-85 nm : SURF facilities at 229 MeV beam energy nm : LASP facilities D 2 lamp Measure transmission after exposure Use results in TSIS SIM exposure scenario (Channel duty-cycling) Richard - 17

18 Soft X-ray / EUV Exposure (NIST SURF) SURF BL-2 (100 ma) Richard - 18

19 SURF Beamline-2 Setup Filter mech for window holder Filter mech for diode Mount to filter mech To beam 312 window 3001 window (qty 3) BNC access Interface holes to filter mech Left to right positioning in beam line AXUV100 diode Alignment view port Exposed to 380 MeV beam Exposed to 229 MeV beam Richard - 19

20 SURF Solar Equivalent Exposures 12 year solar equivalent 22 year solar equivalent 5-year solar equivalent for 5-85 nm 5-year solar equivalent for 2-15 nm BL-2 current (ma) Richard - 20

21 Unprotected Suprasil MeV 380 MeV 70 A-min. dose 12 yr. SE (5-85 nm) 4.5 A-min. dose 22 yr. SE (2-15 nm) Richard - 21

22 380 MeV Induced Degradation 380 MeV 4.5 A-min. dose 22 yr. SE (2-15 nm) The unprotected 3001 Window exposed to the 380 MeV beam showed 0.8% change at 200nm Richard - 22

Protected Suprasil 3001: 380 MeV 2.5-15nm at 22 years solar equivalent This window protected behind the SS312 window, both of which were exposed to the 380 MeV beam.

23 Protected Suprasil 3001: 380 MeV nm at 22 years solar equivalent This window protected behind the SS312 window, both of which were exposed to the 380 MeV beam. This window saw no significant degradation Wet, SS312 Protection Window 312 Protected Window SS312 Window saw small but significant loss of transmission (~0.5% at 200nm) Richard - 23

Rotational feed thru Window mounting arm

24 FUV Exposure Setup: Frankentank Chamber Interior D 2 light Into chamber Rotational feed thru Window mounting arm Aperture 2 Window Housing Window splitter MgF 2 Beam Splitter Diodes Mounting plate Second diode is used to account for the D 2 lamp variability over exposure time Window Identical, empty aperture Richard - 24

25 FUV Exposure ( nm) Residual Gas Analyzer (RGA) Scans Time integrated energy per unit area seen by the window (from D 2 lamp) and solar output in 5 years (1AU). Result: 5+ year solar equivalent dose from about nm. 320 hours Total D 2 lamp exposure Baked out tank until clean criteria: considered clean if all masses above 50 amu are below torr p.p. Measured before and after irradiation Richard - 25

26 FUV Induced Degradation The unprotected 3001 Window exposed to nm Showed 8% change at 200nm Richard - 26

27 Initial Richard - 27

28 Final Richard - 28

29 Surface Cleaning Richard - 29

30 Surface Re-polish : 20 um removed Richard - 30

31 Protected Window Degradation The protected 3001 Window exposed to λ > 200 nm Showed 2% change at 200nm Richard - 31

32 Contamination: Stycast 2850FT One final test was done to test the Suprasil 3001 NUV degradation A sample of Stycast 2850FT was added to the tank The RGA scans of before and after the test still appeared to be fairly clean. In this test we saw an 18% difference at 200 nm in our transmission, from 90% down to 73%. To compare: previous tests gave transmission degradations of only 8%. This gives impetus for rigidly cleaning and baking out all optical cavity components before assembly. *Note the sample was not baked- out before this test Richard - 32

33 Exposure Degradation over Mission Life Richard - 33

Capabilities of NIST SIRCUS for Calibrations of SSI Vis-IR Instruments

Capabilities of NIST SIRCUS for Calibrations of SSI Vis-IR Instruments Steve Brown National Institute of Standards & Technology Gaithersburg, MD steve.brown@nist.gov; 301.975.5167 Answer: Ask LASP folks