“Phase C” Design of the JWST/FGS Tunable Filter Imager TIPS/JIM June 15, 2006 Alex Fullerton STScI / UVic

TIPS/JIM June 15, 2006 Optical Design at PDR Wavelength Coverage SW: 1.2 to 2.1 microns LW: 2.0 to 4.8 microns

TIPS/JIM June 15, 2006 SAT Recommendation Wavelength Coverage SW: 1.2 to 2.1 microns LW: 2.0 to 4.8 microns

TIPS/JIM June 15, 2006 SAT Recommendation Wavelength Coverage SW: 1.2 to 2.1 microns LW: 2.0 to 4.8 microns No cost savings to NASA.

TIPS/JIM June 15, 2006 SAT Recommendation Wavelength Coverage SW: 1.2 to 2.1 microns LW: 2.0 to 4.8 microns No cost savings to NASA. Removes: 1 dichroic beamsplitter 1 pupil/filter wheel assembly 1 Fabry-Perot etalon 1 camera TMA 1 SCA Half an optical bench 80 kg

TIPS/JIM June 15, 2006 SAT Recommendation Wavelength Coverage SW: 1.2 to 2.1 microns LW: 2.0 to 4.8 microns No cost savings to NASA. Removes: 1 dichroic beamsplitter 1 pupil/filter wheel assembly 1 Fabry-Perot etalon 1 camera TMA 1 SCA Half an optical bench 80 kg Hard to achieve science goals with this wavelength coverage!

TIPS/JIM June 15, 2006 FGS-TFI Optical Layout at RDR / Phase C MM Pick-off Mirror Collimator TMA Camera TMA Fabry Perot Filters Fold Detector

TIPS/JIM June 15, 2006 FGS-TFI Optical Layout at RDR / Phase C MM Pick-off Mirror Collimator TMA Camera TMA Fabry Perot Filters Fold Detector

TIPS/JIM June 15, 2006 Fabry-Perot Etalons Optical path difference = 2µl cos  Phase difference = (2  / ) 2µl cos  +  r µ=index of refraction m = 2µl cos  +  r /2  Tuning: For fixed m, on-axis (  =0)  l Detuning: For fixed m, l, off-axis (  )  cos   1   2 /2

TIPS/JIM June 15, 2006 The SAT Challenge: Do More With Less  Improvements with respect to the PDR LW channel: Significantly extended spectral waveband (1.5 to 5 μm) Requirements: 1.6 to 4.9 μm [PDR LW: 2.0 to 4.8 μm] Simplified – just 17 layers ! [PDR LW: 21 layers] Minimal detuning of the etalon with angle-of-incidence An order of magnitude better than earlier versions of this coating!  Non-functional interval between 2.6 and 3 μm Requirements: 2.5 to 3.2 μm System operates at 2.4 μm, where NIRCam is non-functional

TIPS/JIM June 15, 2006 Reflectance and Phase Reflectance Phase (radian) Wavelength (nm) Reflectance Phase Non-Functional Waveband

TIPS/JIM June 15, 2006 Etalon Gap and Spectral Resolution Resolution Gap (nm) Wavelength (nm) Resolution Gap Non-Functional Waveband

TIPS/JIM June 15, 2006 Etalon Detuning - I  max for TFI

TIPS/JIM June 15, 2006 Etalon Detuning - II  max for TFI

TIPS/JIM June 15, 2006 Dual Wheel Configuration at PDR FFCal WCal ND Apo1Apo3 Apo4 Lyot Pupil Wheel Apo2 B1 B2 B3 B4 B5 B6 Open Filter Wheel Spare 8 position Filter Wheel allows for 6 blocking filters, an open for calibrations and one spare 8 position Pupil Wheel allows for a Lyot mask, up to 4 apodization masks, 2 calibration source positions and a neutral density position for target acquisition. Note: Calibration source positions on Pupil Wheel also serve as closed positions for dark calibrations

TIPS/JIM June 15, 2006 Current Dual Wheel Mechanism Nine Position Wheels Motors Resolvers Bracket

TIPS/JIM June 15, 2006 “Phase C” Dual Wheel Design  At least 9 positions are required to cover the full wavelength range (8 blocking filters + 1 “open” position) Otherwise: there is a risk that the wavelength range will be restricted by the blocking filters (not the etalon!)  A larger wheel was not considered (mass).  Spare positions are available in the Pupil / Calibration Wheel Open

TIPS/JIM June 15, 2006 Key Performance Requirements Parent*TFI Requirement DescriptionRequirement ValueDesign Current Value FGS-308TFI Channel FOV> 4.7 sq. arcmin4.88 sq. arcmin FGS-638TFI Pixel Size65 mas64.3 to 65.5 mas FGS-306TFI Wavelength Range 1.6 – 2.5  m 3.2 – 4.9  m 1.5 – 2.7  m 3.1 – 5.0  m FGS-311TFI Spectral Resolution> 70 & < to 105 FGS-315Wavelength Shift in FOV< 1.0% (50% of FOV)< 0.3% (complete FOV) FGS-317 TFI Sensitivity at 3.5  m 126 nJy105 nJy FGS-355Coronagraphic Capability2 Pupil masks 2 Lyot masks 4 Pupil masks 4 Lyot masks NIRCam bandpass TFI bandpass * CSA-JWST-RD-0002 Rev B (JWST-RQMT ) - Wavelength Selection Flexibility - Good Sensitivity for Emission Line Objects - Emission Line Diagnostic Imaging- Coronagraphy for AGN studies & Extrasolar Planet Spectra

TIPS/JIM June 15, 2006 Etalon Stability / Repeatability  Stability depends on temperature control of etalon electronics Etalon gap changes by 0.12 nm/K with prototype ECE Issue: will flight electronics exhibit a temperature drift? Assume: 1.2 nm/K (  10 worse) Implement: temperature control in ECE; stable to ~1 K Expect: Over the course of a typical observation, etalon gap may vary by ~1.2 nm, or ~7% of a resolution element at 1.5  m. This is consistent with scientific requirements for photometric stability. Can use onboard calibration lamp to check gap spacing during particularly long/critical observations.  Repeatability will depend upon the interval in question. Over ~month, expected to be the same as the stability Over longer intervals, will depend on aging of components Mitigate by checking/updating TFI wavelength calibration