NASA GSFC s CHARMS Facility

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Sophia Mason
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$limits on accuracy in minimum deviation refractometry design approach / measurement technique for highest accuracy technologies we rely on data products$

1 NASA GSFC s CHARMS Facility Doug Leviton / NASA GSFC / Optics Branch with Manuel Quijada and Ross Henry what is CHARMS? limits on accuracy in minimum deviation refractometry design approach / measurement technique for highest accuracy technologies we rely on data products and examples materials we ve measured

2 What is CHARMS? Cryogenic High Accuracy Refraction Measuring System developed in ~003 to support design of JWST s NIRCam all refractive optical design with two triplet lenses of ZnSe, LiF, BaF differential, absolute, minimum deviation refractometer dense sampling in both wavelength and temperature current wavelength coverage: 400 nm (violet) to 5.6 microns in mid-ir aiming to extend range to 10 nm in FUV, and 0 microns in mid-ir temperature coverage 15 K to 330+ K (60 C) rated accuracy +/ to +/ depending on material and temperature

3 Measuring angles in refractometry apex: measure angle of prism face A measure angle of prism face B measure direction of undeviated beam measure direction of deviated beam for each wavelength n abs (,T) = sin (/ + /) / sin (/) (T) A B (,T)

4 Limits on accuracy in minimum deviation refractometry n(α, δ(λ, T)) explore dn/dα Δα Prism apex dn/dδ Δδ Deviation angle dn/dλ Δλ Spectral dispersion dn/dt ΔT Thermo-optic coefficient uncertainty should be listed as a function of both wavelength AND temperature

5 Textbook uncertainties Sources of uncertainty in measuring absolute index giving n = 1 x 10-6 for example, in air with a Ge prism of 17 of index 4. at.5 m apex angle (arcseconds) ± half-deviation angle (arcseconds) ± 0.04 level (arcminutes) + 9 sample temperature (C) ± 0. wrt T standard (15 C) air temperature (C) ± 0.6 wrt T standard (15 C) atmos. pressure (mm Hg) ± 1.9 wrt P standard (760 mm) humidity (H 0 mm Hg) ± 3 wrt dry air (0 mm) wavelength (nm) ± 0.03 Aspects with black arrows need not be considered for measurements in vacuum, i.e. absolute measurements

6 Example for absolute accuracy in IR Demonstrated capabilities of CHARMS in vacuum at any temperature and associated uncertainties in n x 10 6 for Ge prism of apex 17 and index 4. at.5 m wavelength capability n x 10 6 apex angle (arcseconds) ± half-deviation angle (arcseconds) ± level (arcminutes) +9 1 sample temperature (C) ± wavelength (nm) ± RSS uncertainties n abs < 5 x 10-5 This uncertainty may be different and should be so stated for each wavelength, temperature for a given prism specimen

7 Bookkeeping error budget index n apex α deviation δ dn/dλ dn/dt dn/dα dn/dδ dλ dt da dδ dn SENSITIVITIES FOR SPECIFIED PRISM FOR SPECIFIED PRISM index n apex a alpha delta d dn/dwv dn/dt dn/da dn/d dwv dn(dwv) dt dn(dt) da dn(da) dd dn(dd) dn r.s.s deg rads deg rads /nm /K -.64/rad 5.690/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -6.4E deg 5.4 sec ### 1.5E E rads deg rads /nm /K -1.35/rad.786/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -3.3E deg 5.4 sec ### 7.3E E rads deg 0.50 rads /nm /K -0.93/rad 1.789/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -.3E deg 5.4 sec ### 4.7E E rads deg rads /nm /K -0.73/rad 1.67/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -1.8E deg 5.4 sec ### 3.3E E rads deg rads /nm /K -0.63/rad 0.93/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -1.5E deg 5.4 sec ###.4E E rads deg rads /nm /K -0.58/rad 0.730/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -1.4E deg 5.4 sec ### 1.9E E rads deg 0.83 rads /nm /K -9.7/rad 5.588/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -.3E deg 5.4 sec ### 1.5E E rads deg rads /nm /K -6.7/rad 3.603/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -1.5E deg 5.4 sec ### 9.4E-05 1.E rads deg rads /nm /K -4.80/rad.569/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -1.E deg 5.4 sec ### 6.7E E rads deg rads /nm /K -3.95/rad 1.910/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -9.7E deg 5.4 sec ### 5.0E E rads deg rads /nm /K -3.4/rad 1.49/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -8.4E deg 5.4 sec ### 3.7E E rads deg 0.47 rads /nm /K /rad 5.479/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -3.4E deg 5.4 sec ### 1.4E E rads deg rads /nm /K /rad 3.734/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -.5E deg 5.4 sec ### 9.8E-05 1.E rads deg rads /nm /K -8.03/rad.707/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -.0E deg 5.4 sec ### 7.1E E rads deg 1.08 rads /nm /K -6.75/rad 1.994/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -1.6E deg 5.4 sec ### 5.E E rads deg rads /nm /K /rad 5.377/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -4.3E deg 5.4 sec ### 1.4E E rads deg rads /nm /K /rad 4.134/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -3.5E deg 5.4 sec ### 1.1E E rads deg rads /nm /K -11.9/rad 3.67/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -.9E deg 5.4 sec ### 8.6E E rads deg rads /nm /K /rad.608/rad 0.10 nm 4.0E K 1.E deg 0.5 sec # -.5E deg 5.4 sec ### 6.8E E-05 uncertainty governed by all eight quantities in the red box for each measurement for a given specimen (green box) so, a refractometer should not list a single number for accuracy

8 On precision CHARMS precision for fused silica at a given wavelength precision often well exceeds and should not be confused with accuracy Typical day-to-day repeatability Absolute refractive index Day 1 Day Day 3 Day 4 Day 5 Day 6 Day Temperature [K]

9 CHARMS design approach / measurement technique limit contribution of each error source by design / know each contributor well automate to eliminate human factor build best practical machine for measuring apex angle use similar hardware for measuring beam direction in refractometer use multiple, calibrated high accuracy temperature sensors calibrate monochromator carefully with laser lines and measure only at wavelengths for calibrated order number wavelength make differential measurements have access to undeviated beam and refer to it frequently! measure spectral index over and over as temperature of sample slowly drifts in temperature builds rich data set for fitting immerse entire refractometer in vacuum measurements thus absolute no window effects eliminates most environmental effects all reflective design: broadband and achromatic

10 CHARMS optical layout cryo-refrigerator chamber f = 1.1 m rotating flat prism monochromator exit slit MIR camera slit image flat flat flat flat UVIS camera f = 1.5 m 0.5 m

11 CHARMS opto-mechanical layout monochromator (not shown) rotating fold flat sample chamber shield fixed fold flat collimator cryo refrigerator focus flat camera mirror UVIS camera detector select mirror MIR camera (not shown) collimator fold flat

12 Technologies we rely on high accuracy, high resolution, absolute Leviton encoders installed on apex measuring setup rotating fold mirror spindle sample stage monochromator grating shaft absolute electronic autocollimator long focal length collimating and camera mirrors high accuracy calibrated Si diode temperature sensors CCD for NUV/Vis/NIR wavelengths InSb array camera for NIR to mid-ir wavelength QTH and globar light sources numerous order sorting filters

13 Calibrated monochromator monochromator grating encoder scale encoder LED illumination encoder camera

14 Sample assembly sample chamber prism sample platform sample isolator scale hold-down encoder scale precision bearing thermal isolators

15 CHARMS automation Rack contains: control PC motor controllers encoder readouts temperature monitors programmed power supplies turbopump control pressure gauges monochromator control

16 Standard data product: Sellmeier Model ) ( j i i i i i j ij i T S T S T S T S S T S T S m 1 i i i (T) (T) S 1,T) ( n ) ( 3 ) ( 3 ) ( ) ( ) ( 1 ) ( 1 1 ), ( T T S T T S T T S T n, where

17 Prismatic Specimens Measured optical properties of JWST NIRCam lens materials ZnSe - 9 BaF -58 LiF - 60

18 Absolute refractive indices of BaF absolute refractive index Absolute refractive index of Barium Fluoride with temperature wavelength [microns] 50 K 60 K 70 K 80 K 90 K 100 K 110 K 10 K 150 K 00 K 50 K 75 K 95 K 300 K

19 Absolute refractive indices of LiF absolute refractive index Absolute refractive index of Lithium Fluoride with temperature wavelength [microns] 65 K 70 K 75 K 80 K 90 K 100 K 10 K 150 K 00 K 50 K 75 K 95 K 300 K

20 Absolute refractive indices of ZnSe Absolute refractive index of ZnSe with temperature absolute refractive index wavelength [microns]

21 Spectral dispersion in BaF dispersion [1/microns] Spectral dispersion in Barium Fluoride with temperature 50 K 150 K 95 K wavelength [microns]

22 Spectral dispersion in LiF Spectral dispersion in Lithium Fluoride with temperature dispersion [1/microns] K 150 K 95 K wavelength [microns]

23 Spectral dispersion in ZnSe dispersion [1/microns] Spectral dispersion in Zinc Selenide with temperature 0 K 150 K 95 K wavelength [microns]

24 Thermo-optic coefficient (dn/dt) for BaF Thermo-optic coefficient for Barium Fluoride with temperature 0.E+00 dn/dt [1/K] -1.E K 80 K 100 K 10 K 150 K 00 K 95 K -.E wavelength [microns]

25 Thermo-optic coefficient (dn/dt) for LiF Thermo-optic coefficient for Lithium Fluoride with temperature dn/dt [1/K] 0.E+00-5.E-06-1.E-05 -.E K 80 K 10 K 150 K 00 K 50 K 95 K -.E wavelength [microns]

26 Thermo-optic coefficient (dn/dt) for ZnSe Thermo-optic coefficient for Zinc Selenide with temperature 1.5E-04 dn/dt [1/K] 1.0E E-05 0 K 40 K 60 K 80 K 100 K 00 K 95 K 0.0E wavelength [microns]

Measurement campaigns to date JWST / NIRCam BaF Ge, LiF, Si, ZnS, ZnSe Ball Aerospace / Kepler Photometer Corning 7980 fused silica (5 samples from 1 m corrector boule) ESO / ESA ZnSe Harvard

27 Measurement campaigns to date JWST / NIRCam BaF Ge, LiF, Si, ZnS, ZnSe Ball Aerospace / Kepler Photometer Corning 7980 fused silica (5 samples from 1 m corrector boule) ESO / ESA ZnSe Harvard College Observatory S-TIM 8 UC Lick Observatory CaF, S-FTM16, S-FPL15 University of Oxford BaLKN3, E-SF03, N-BK7, SF15 NASA proposals Corning 7940, CaF, Infrasil 301, SF4, SF6, S-TIH1 We want you!

Temperature-dependent refractive index of CaF 2 and Infrasil 301

$Temperature-dependent refractive index of CaF 2 and Infrasil 301$ Temperature-dependent refractive index of CaF 2 and Infrasil 301 Douglas B. Leviton!, Bradley J. Frey, Timothy J. Madison NASA Goddard Space Flight Center, Greenbelt, MD 20771 ABSTRACT In order to enable