ZTF Optics Design P. Jelinsky ZTF Technical Meeting 1

Optics Outline Overview of Requirements Trade Studies Conceptual Design Future Work ZTF Technical Meeting 2

Requirements Overview Use the Oschin Schmidt telescope primary and corrector Illuminate 12 CCD231-C6 e2v detectors (6k x 6k, 15 µm pixels (~ 1 arcsecond)) –16 detectors had large vignetting and worse imaging (see next slide) R band average FWHM < 1.1 arcseconds (final, including alignment and manufacturing) –Allow 1.0 arcseconds for the optical design G band average FWHM < 1.2 arcseconds (final, including alignment and manufacturing) –Allow 1.1 arcseconds for the optical design Use materials that transmit in the U and I band –May add these filters later ZTF Technical Meeting 3

Requirements Overview (continued) ZTF Technical Meeting 4 Detector Pattern (with vignetting) No Vignetting 10%Vignetting 20%Vignetting 30%Vignetting

Initial Trade Study Inputs Distance from flattener to CCD is >= 2mm Allow distance from Schmidt corrector to mirror to vary Window diameter/thickness <= 14.4 (same as QUEST camera) –Safe to have atmospheric pressure across Window is Fused Silica All spherical surfaces –Aspheric surfaces did not change performance much Optimize over 5 wavelengths in the g’, r’ bands as below (allowing a focus change). Optimize over 9 field points Merit function is the 2D FWHM (RMS radius * ) ZTF Technical Meeting 5

Bandpass Definition ZTF Technical Meeting 6 u’g’r’i’ Wavelength (nm) Wavelength (nm) Wavelength (nm) Wavelength (nm)

Initial Trade Study Initially did not include a filter in the trade study and concentrated only on the R band –Filter seemed to always make design worse Quicker to analyze to limit trade space ZTF Technical Meeting 7

Initial Trade Study ZTF Technical Meeting 8 DesignDescriptionG Band FWHM R Band FWHM Classical Schmidt (just for a limiting case) 0.78” 0.65” Curved Focal Plane Powered window 1.85” 1.48” Flat focal plane Powered window 2.20” 1.86” 4 segment focal plane 4 segment window 1.53” 1.21” No designs with flat detectors and vacuum windows met requirements

12 Segment Focal Plane Schematic ZTF Technical Meeting 9 Filter Window 12 flatteners 12 detectors

12 Segment Focal Plane Schematic Each detector is flat but tilted with respect to the others (see previous slide) –12 chords on focal plane One vacuum window for all detectors (see previous slide) –After FEA center thickness fixed at ~22mm Each detector has its own field flattener (see previous slide) –Allow field flattener to be decentered and tilted ZTF Technical Meeting 10

12 Segment Telescope Schematic ZTF Technical Meeting 11 CorrectorPrimaryFocal Plane Corrector and primary are used as built –Corrector is moved 31mm farther from primary (then PTF) Dewar is “hidden” behind the filter –Obscuration dominated by the filter and its mount

Detector Optical Surface Field Flattener Detector Gap If t is the thickness of the flattener, d is the distance from detector to the flattener, c is the chamfer of the flattener, g is the gap between the flatteners, f is the f/# of the beam, n is the index of refraction of the glass, and s is the spacing between the optical surface of the detectors, then For g = 2mm, c = 1mm, t = 5mm, d=2mm, f=2.5, n = 1.5 then s = 8.2 mm –I assumed 8.4 mm in the analysis (closest allowed given e2v packaging) ZTF Technical Meeting 12

12 Segment Focal Plane Inputs Distance from flattener to detector > 2mm (smaller preferred) Distance from flattener to window from 3 mm to 110 mm –optics prefers larger; obscuration prefers smaller Distance from window to filter from 15 mm to 110 mm –optics prefers larger; obscuration prefers smaller Filter, Window, and flatteners are Fused Silica –Good transmission in UV and IR Only Optimized G and R band simultaneously (allowing focus change) Optimize over 5 wavelengths in the g’, r’ bands Optimize over 9 field points in each detector Merit function is the average 2D FWHM (RMS radius * ) –Use RMS field map with 50 x 50 points ZTF Technical Meeting 13

12 Segment Focal Plane Trends Thicker Windows degrade optical performance –22mm center window thickness gives factor of safety of 8 (from FEA analysis) Thicker filter degrades optical performance Flat filter degrades optical performance Larger CCD – flattener spacing degrades optical performance ZTF Technical Meeting 14

12 Segment Trade Study PTF Corrector Distance = mm; Original Corrector Distance = mm (A) = asphere; (S) = sphere ZTF Technical Meeting 15 CaseFilterWindowFlattenerR Band FWHMG Band FWHM Corrector Distance IMeniscus (5mm)Meniscus(A)Off axis9.1µm (0.60”)13.2µm (0.88”) mm IIMeniscus (5mm)Plano-Concave(S)Off axis9.1µm (0.61”)14.1µm (0.94”) mm IIIMeniscus (5mm)Meniscus(A)On axis9.0µm (0.60”)14.1µm (0.94”) mm IVMeniscus (5mm)Plano-Concave(S)On axis9.1µm (0.61”)14.0µm (0.93”) mm VMeniscus (5mm)Meniscus(A)Identical9.0µm (0.60”)13.7µm (0.92”) mm VIMeniscus (5mm)Plano-Concave(S)Identical9.4µm (0.63”)13.9µm (0.92”) mm VIIPlano-Convex (5mm)Concave-Plano(S)Off axis9.4µm (0.63”)14.8µm (0.98”) mm VIIIPlano-Convex (5mm)Concave-Plano(S)On axis9.4µm (0.63”)16.8µm (1.12”) mm IXPlano-Convex (5mm)Concave-Plano(S)Identical9.5µm (0.63”)16.8µm (1.12”) mm XMeniscus (10mm)Meniscus(A)Off axis9.7µm (0.65”)14.5µm (0.97”) mm XIMeniscus (10mm)Meniscus(S)Off axis9.8µm (0.65”)15.5µm (1.04”) mm XIIMeniscus (10mm)Meniscus(S)On axis9.8µm (0.65”)15.5µm (1.03”) mm XIIIMeniscus (10mm)Meniscus(S)Identical10.1µm (0.67”)15.5µm (1.04”) mm XIVPlano-Convex (10mm)Biconcave(S)Identical9.7µm (0.65”)16.8µm (1.12”) mm XVPlano-Convex (5mm)Biconcave(S)Identical9.1µm (0.60”)14.9µm (1.00”) mm XVIPlano-Plano(10mm)Meniscus(A)Identical20.5µm (1.37”)27.7µm (1.85”) mm XVIIPlano-Plano(10mm)Meniscus(A)Off axis20.5µm (1.37”)27.9µm (1.86”) mm XVIIIPlano-Plano(5mm)Meniscus(A)Off axis18.0µm (1.20”)24.6µm (1.64”) mm

Case XV Imaging Results (1 Quadrant) R Band average FWHM = 0.60 arcseconds; maximum FWHM = 0.88 arcseconds G Band average FWHM = 1.00 arcseconds; maximum FWHM = 1.26 arcseconds ZTF Technical Meeting 16 R BandG Band FWHM (arcseconds)

Future Work Complete I and U band results of current system (quick) Complete optical tolerance analysis –Budget/split tolerances into telescope and cryostat sections E.g. filter location (part is telescope filter mechanism/ part is cryostat manufacture) Complete manufacturability/cost studies Add guider and its optics to the system Complete vignetting/obscuration analysis Complete ghosting/scattered light analysis ZTF Technical Meeting 17

BACKUP SLIDES ZTF Technical Meeting 18

Detector Layout Two Detectors layouts have been considered –Minimize the gap in each direction (asymmetrical, need 3 detectors in Zemax) –Place detectors centers on a square grid (symmetrical, need 2 detectors in Zemax) ZTF Technical Meeting 19 Only the minimize gap has been studied at the moment The square grid version will be a slight modification to the optics DetectorX (mm)Y (mm)xfield ( o )yfield ( o ) Field locations for minimum gap DetectorX (mm)Y (mm)xfield ( o )yfield ( o ) Field locations for square grid

RMS Zemax settings RMS field map settings –Ray density = 6 –Data = Spot Radius –Wavelength = All –Method = Gauss Quad –Center field = 5 –Refer To = Centroid –X field size = –Y field size = –X field sampling = 50 –Y field sampling = 50 –Surface = Image Use the text->Window->Copy clipboard to place the data into excel for analysis ZTF Technical Meeting 20

Case XV Optical Prescription (Detector 1) ZTF Technical Meeting 21 #TypeSurface ROC = (1/c) (mm) Thickness (mm) Glass Diameter (mm) A2A2 A4A4 A6A6 A8A8 1STANDARDCORRECTOR LLF EVENASPHCORRECTOR BK E EVENASPHCORRECTOR E E-200 4STANDARD Infinity STANDARDM MIRROR STANDARDR band FocusInfinity STANDARDG band FocusInfinity STANDARDfilter SILICA STANDARD Infinity EVENASPHwindow SILICA EVENASPH STANDARDDet 1 focusInfinity Decenter XDecenter YTilt XTilt Y 13COORDBRKFlat1 tiltInfinity STANDARDDet1 flat SILICA STANDARD Infinity Decenter XDecenter YTilt XTilt Y 16COORDBRKDet1 TiltInfinity STANDARDFILMInfinity

Case XV Optical Prescription (Detector 2) ZTF Technical Meeting 22 #TypeSurface ROC = (1/c) (mm) Thickness (mm) Glass Diameter (mm) A2A2 A4A4 A6A6 A8A8 1STANDARDCORRECTOR LLF EVENASPHCORRECTOR BK E EVENASPHCORRECTOR E E-200 4STANDARD Infinity STANDARDM MIRROR STANDARDR band FocusInfinity STANDARDG band FocusInfinity STANDARDfilter SILICA STANDARD Infinity EVENASPHwindow SILICA EVENASPH STANDARDDet2 focusInfinity Decenter XDecenter YTilt XTilt Y 18COORDBRKFlat2 tiltInfinity STANDARDDet2 flat SILICA STANDARD Infinity Decenter XDecenter YTilt XTilt Y 21COORDBRKDet2 tiltInfinity STANDARDFILMInfinity

Case XV Optical Prescription (Detector 3) ZTF Technical Meeting 23 #TypeSurface ROC = (1/c) (mm) Thickness (mm) Glass Diameter (mm) A2A2 A4A4 A6A6 A8A8 1STANDARDCORRECTOR LLF EVENASPHCORRECTOR BK E EVENASPHCORRECTOR E E-200 4STANDARD Infinity STANDARDM MIRROR STANDARDR band FocusInfinity STANDARDG band FocusInfinity STANDARDfilter SILICA STANDARD Infinity EVENASPHwindow SILICA EVENASPH STANDARDDet3 focusInfinity Decenter XDecenter YTilt XTilt Y 23COORDBRKFlat3 tiltInfinity STANDARDDet3 flat SILICA STANDARD Infinity Decenter XDecenter YTilt XTilt Y 26COORDBRKDet3 tiltInfinity STANDARDFILMInfinity