Sylvia Baggett (STScI) Ray Boucarut (GSFC)

1. WFC3 Replacement Filters Sylvia Baggett (STScI) Ray Boucarut (GSFC) GSFC Randal Telfer Manuel Quijada Petar Arsenovic Morgan Dailey Randy Kimble Jeff Kirk Tim Madison Steve Rice Jennie Chu Brad Greeley Jackie Townsend Lori Tyahla Weijun Su STScIJessica Kim Quijano Tom Brown George Hartig John MacKenty Massimo Robberto Barr George Allen Kevin Downing John Potter

2. Outline • Introduction • Procurement of replacements • Characterization of candidates • Approved filters • Replacement status

3. Flight SOFA Introduction WFC3 designed as a two-channel instrument UVIS Channel SOFA: 12 wheels, each with 4 filters + clear 63 filters (includes 5 quads, 1 grism) x12 • Excellent performance from 51 of 63 UVIS filters, majority consistent with spec but instrument level testing showed filter ghosts in some filters • Procurement of replacements: new technology provides reduction in ghosts and frequently an improvement in throughput as well IR Channel 17 filters (15 filters and 2 grisms) • Excellent performance from all IR filters, consistent with spec; no ghosts • Procurement of replacements for two filters to add blue blocker (new substrate-removed IR detector has significant QE in blue); addition of new red edge coat to grism (G141), to block higher background seen in TV data

4. Flight F225W ~15% total UVIS filter ghosts: airgap design Filter ghosting due to design of element (either air-gap or multi-substrate) • UV and narrowband air-gaps • Ghosts show elaborate shapes • Strong field dependence: both position of ghost relative to source and morphology of ghost • Strength varies with wavelength and peaks outside of bandpass Image from WFC3 ISR 2004-04

5. AR coating Coating Substrate BK7 Epoxy Coating Substrate GG435 Epoxy Substrate BK7 Coating AR coating UVIS filter ghosts: multi-substrate design Flight – monochromatic • VIS/medium bands • Compact, pointlike ghosts • Strong wavelength dependence • (strongest out of band) • Slight field dependence 470nm F606W: multi-substrate construction Epoxy layer << air gap 500nm Flight – whitelight Instrument-level results<0.1% each ~0.3% total in spots 725nm Expected window ghosts Brightest spot ~24% peak at 470nm Stimulus artifact

6. Working Plan With Science Oversight Committee recommendation, focus has been on obtaining and testing the following new UVIS filters • UV (F218W, F225W, F275W, F300X) • F606W • Medium bands (F410M, F467M, F621M, F689M) • Narrowbands (F656N, F658N – plus F280N) Green: high priority Blue: medium priority Red: low priority

7. Manufacturing Process Barr Associates, Lead: George Allen Polish glass Verify thickness, flatness, wedge, surface quality Procure substrate Check index of refraction Radiation tests Receive customer requirements Design filter Input from GSFC/IPT/SOC Predict ghost level Measure bandpass And blocking Shape glass Deposit coatings Inspect and label selected filters Search for blemishes, scratches, Cosmetic defects. (UV: paint pinholes) Ship to GSFC for characterization tests Test witness samples (abrasion, adhesion, humidity, temperature)

8. Characterization Test Flow Receipt of filter from Barr Tests by vendor (such as thickness, flatness, wedge, surface quality, bandpass, blocking, cosmetics) Analysis by filter team Confirm dimensions; check for blemishes Inspection Front/backlit photos Results presented and discussed (GSFC/IPT) Whitelight + monochromatic ghost levels Imaging Wavefront and wedge verification Focal shift confirmation Final results posted to GSFC WWW Spectral Scans Inband scans in 5x5 grid Out of band scans in 5 positions SOC/IPT/GSFC choose flight/spare Flatfields Check for coating problems Environmental tests on witness pieces Verify no changes

9. 200 pixels Flight – whitelight instrument-level tests Source in each quad center Brightest ghost ~10%; totals ~15%. Example: F225W Before After F225W-303 – images taken in lab at 16 UVIS field points and mosaic’d together into relative positions on WFC3 FOV 1” Setup ghost Filter ghost <0.3%

10. Approved UV filter set In all cases, ghosting has been reduced and in most cases, other improvements were achieved as well such as simplified ghost shapes (thanks to switch from air-gap to single substrate design), higher grasp, better uniformity. Transmission curves of replacement and original flight filters

11. In all cases, ghosts have been reduced (or eliminated) and grasp improved. Approved Medium Bands Original medium band filters consisted of layers of substrates with coatings on both sides joined with epoxy – giving rise to numerous small, pointlike ghosts. In the new filters, bandpass coatings are on one side, AR coat on the other. Transmission curves of replacement and original flight filters

12. Installing New F606W

13. = high priority 1 4 11 3 6 7 8 9 UVIS Filter Status at a Glance DONE DONE N/A DONE DONE N/A Wheels Slots F300X F225W F280N F606W F621M F275W F467M F689M F658N F656N F218W F600LP F547M F410M fatUV Made at Barr Tested @GSFC Approved by SOC Sent to Ball F689M, F658N replacement deemed not worth risk Original F600LPflight spare fully tested. New filter from Barr to serve as spare. F656N replacement deemed not worth risk. New F280N to go into F280N slot (fatUVs not useful). Legend done in progress DONE = old filters removed, new installed; wheels air-cured and baked