The TSIS Spectral Irradiance Monitor: Prism Optical...

Richard - 1 Transmission Degradation for TSIS SIM SSI Variations Workshop 2/ 28- 3/1, 2012 (NIST Gaitherburg)

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The TSIS Spectral Irradiance Monitor: Prism Optical Degradation Studies

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!!


• 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?

TSIS Optical Degradation Trade Study


TSIS SIM Development Approach TSIS SIM designed for long-term spectral irradiance measurements (climate research) 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 3rd 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)

SORCE SIM

TSIS SIM


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


Aperture area ESR

Absorptance

prism transmission

Slit diffraction

Spectral Transfer function

Measurement Equation Overview

ESR detected power


Overview of TSIS SIM

Vacuum Door Mechanism

ESR Detector Assy

Fery Prism Assy Shutter/Photodiode Assy

CCD Assy

Fine Sun Sensor

Focal Plane Module

CCD Aperture Ch. A Aperture Ch. B Aperture Ch. C Aperture

Rotational Prism Carrier

External Flex


Train wreck occurs here!

Prism Assembly


• 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

Material Considerations for Refractive Optics


Fresnel Refl. Loss Suprasil 1 / 2A Suprasil 311 / 312 Suprasil 300 / 3001

TSIS SIM Level 1 wavelength range

Suprasil (Fused Silica) Transmission


• Suprasil 3001 is a high purity synthetic fused silica manufactured by flame hydrolysis of SiCl4

• High index homogeneity – ∆n/n ≤ 1 ppm over CA volume (optically isotropic “3D”-material) – No striations

• Low NIR absorption – Low OH & trace impurities

• 0.25 ppm/cm @ 1064 nm

• 1 ppm/cm @ 1319 nm

Suprasil 3001 Properties


< 300 ppb/cm!

Refractive Index Homogeneity


Full Spatial & Spectral Transmission Mapping Prism measurement geometry is for ESR optical path Stabilized SIRCUS lasers cover 211 – 2400 nm range

Transmission measured over 10 x 10 grid for both s and p-polarizations

Refraction vs. wavelength (Suprasil 3001 fused silica)


Prism Transmission

55 λ’s x 100 spatial points x 2 polarizations x 4 prisms = 44,000 measurements! (5 months effort)


• Fabricate 6 super-polished (SR < 1 ÅRrms ) Suprasil 3001 window samples (same material and process as prisms) and 2 super polished Suprasil 312 windows

• Measure initial transmission from 200-850nm • Expose different windows to the equivalent of a 5-year solar dose

(15 orbits/day 218 days/year) at three different wavelength regions: – 2.5-15 nm : SURF facilities at 380 MeV beam energy – 5-85 nm : SURF facilities at 229 MeV beam energy – 112-165 nm : LASP facilities D2 lamp

• Measure transmission after exposure

• Use results in TSIS SIM exposure scenario (Channel duty-cycling)

Suprasil 3001 Degradation Study


Soft X-ray / EUV Exposure (NIST SURF)

SURF BL-2 (100 mA)


Mount to filter mech

3001 window (qty 3) 312 window

Interface holes to filter mech

Left to right positioning in beam line

Alignment view port

AXUV100 diode

To beam

Filter mech for diode Filter mech for window holder

BNC access

Exposed to 380 MeV beam

Exposed to 229 MeV beam

SURF Beamline-2 Setup


SURF Solar Equivalent Exposures

5-year solar equivalent for 5-85 nm

5-year solar equivalent for 2-15 nm

12 year solar equivalent

22 year solar equivalent

BL-2 current (m

A)


229 MeV 380 MeV 70 A-min. dose 12 yr. SE (5-85 nm)

4.5 A-min. dose 22 yr. SE (2-15 nm)

Unprotected Suprasil 3001


The unprotected 3001 Window exposed to the 380 MeV beam showed 0.8% change at 200nm

380 MeV 4.5 A-min. dose 22 yr. SE (2-15 nm)

380 MeV Induced Degradation


“Wet”, SS312 Protection Window

2.5-15nm at 22 years solar equivalent

Protected Window

This window protected behind the SS312 window, both of which were exposed to the 380 MeV beam. This window saw no significant degradation

SS312 Window saw small but significant loss of transmission (~0.5% at 200nm)

312

“Protected” Suprasil 3001: 380 MeV


Rotational feed thru

D2 light Into chamber

Window splitter

Mounting plate

Window mounting arm Chamber Interior

Diodes MgF2 Beam Splitter

Aperture 2

Window Identical, empty aperture

Second diode is used to account for the D2 lamp variability over exposure time

Window Housing

FUV Exposure Setup: “Frankentank”


Time integrated energy per unit area seen by the window (from D2 lamp) and solar output in 5 years (1AU). Result: 5+ year solar equivalent dose from about 112-165 nm.

FUV Exposure (112-165 nm)

Baked out tank until “clean” • criteria: considered clean if all masses above 50 amu are below 10-10 torr p.p.

Measured before and after irradiation

320 hours Total D2 lamp exposure

Residual Gas Analyzer (RGA) Scans


The unprotected 3001 Window exposed to 112-165 nm Showed 8% change at 200nm

FUV Induced Degradation


Initial


Final


Surface Cleaning


Surface Re-polish : 20 um removed


Protected Window Degradation

The protected 3001 Window exposed to λ > 200 nm Showed 2% change at 200nm


• 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

Contamination: Stycast 2850FT


Exposure Degradation over Mission Life

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