1. Optical Subsystem Roy Esplin Dave McLain

2. Internal Optics Bench Subassembly 2 Gut Ray Dichroic Beamsplitter (MWIR reflected, LWIR transmitted) LWIR Lens Cold Entrance Aperture Fold Mirror MWIR Lens Fold Mirrors Thermal Isolator Mount LN2 Heat Exchanger LWIR FPA Fold Mirror (MWIR Grating Replacement) LWIR Grating

3. Cold Entrance Aperture Position of cold aperture precisely controlled by mounting cold aperture assembly on MWIR/LWIR dichroic mount Cold aperture covers larger hole in cold shield that is less accurately positioned Cold aperture size can be changed by replacing the aperture assembly Making this cold aperture the aperture stop rather than the telecope exit pupil would reduce the sensitivity to temperature changes of the optics in front of COB, but it would decrease the optical throughput. 3 Cold Aperture Assembly Cold Shield MWIR/LWIR Dichroic Mount Replacement P2 Splitter Mount

4. Optical Design Highlights New optical prescriptions for the Port 4 (LWIR) and Port 3 (MWIR) were developed starting from the ZMAX prescriptions MASModelPort4.zmx and MASModelPort3.zmx and provided to SDL by UCSC New optical prescriptions use the telescope ±0.065º by ±0.065º IFOV used in MASModelPort4.zmx and MASModelPort3.zmx Telescope field stop 0.381 mm x 0.381 mm, entrance pupil diameter 150mm, afocal magnification 6X, exit pupil diameter 25 mm Lenses optimized together with the telescope and other optics in front of COB using Code V LWIR prescription name: EMAS_Port4_V5f_Cold.len MWIR Single-Element prescription name: EMAS_Port4_SE_V2f_Cold.len MWIR Path-Forward prescription name: EMAS_Port3_V3e_Cold.len Focal length of both the LWIR and MWIR lenses combined with the telescope is 250 mm. The focal length for the lenses alone is 250/6=41.7 mm Lens optimized with operational temperature indices of refraction Fabrication specifications for lens radii and the length of lens spacers adjusted for CTE difference between operational and ambient temperatures 4

5. 5 Lens elements made of Germanium and ZnSe as shown on drawing View looking down at lens shows direction of dispersion Rays for only bands L1 and L12 are shown 5 LWIR Lens ZnSe Ge ZnSe Ge

6. Location of L1 Image of Field Stop 6 LWIR Grating LWIR Fold Mirror LWIR Filter L1 rays (Zoom 1) L1 Image of Field Stop

7. LWIR Lens Elements 7 Lens 1 Lens 3 Lens 2 Lens 4 Lens 5 Coatings R ≤ 1.5% avg. 6.4µm-14.0µm wavelengths both ZnSe & Ge elements Supplier: RMI

8. MWIR Single-Element Lens 8 Lens Material: Silicon First surface, S2 is an ellipse with conic constant K= -0.112339 Coating R ≤ 1.0% avg. 3.0 µm - 5.0 µm wavelengths Supplier: ISP

9. Worst-Case Total Wavefront Errors (Design Residual + 2σ Tolerance Contribution) Worst-case means across IFOV Optics with a wavefront error of 0.07 RMS waves are essentially diffraction limited Tolerances include all optical components including nominal tolerances on telescope and other optics in front of COB 1 mrad primary tilt 1.5 mrad secondary tilt 9

10. Lens barrel showing spring-loading of lenses 10

11. Lens barrel with first element removed to show hard stops for radial locating 11

12. Selection of Grating Blaze Wavelength 12 9.73 µm Blaze Selected

13. Incidence and Diffracted Rays for 9.730 µm Wavelength 13 Incident Gut Ray Diffracted Gut Ray at 9.730 µm Grating Bisector of Angle Formed by Incident and Diffracted Rays is Facet Normal LWIR Fold Mirror LWIR Lens

14. Plane of Grating facet and Plane Containing Incident and Diffracted Rays and Facet Normal for 9.730 µm Wavelength 14 Plane of Grating Facet Plane of Incident & Diffracted Rays and Facet Normal at 9.730 µm Diffracted Gut Ray at 9.730 µm Incident Gut Ray Facet Normal

15. Grating Blazed for 9.730 µm Wavelength with Facets Shown Oversize (Grating Blaze Angle 15.73º) 15 Yellow Line Outlines Plane of Grating Facet

16. Grating 16 Material: Stress-Relieved Aluminum Type: Original Burnished Rulings Coating: Gold Grating spacing: 0.020 mm Ruling Spatial Frequency: 50 lines/mm Operational temperature: 80K

17. Optical Beam Footprint on Grating 17

18. LWIR Images of Field Stop on Detector Array 18 BandCENTER WAVELENGTH label(µm) L16.715 L27.325 L38.280 L48.550 L59.730 L610.200 L711.030 L812.020 L912.600 L1013.335 L1113.635 L1213.935

19. LWIR Detector Active Areas & Field Stop Images 19 Dimensions: millimeters (mm) Solid lines: Active Areas Phantom Lines: Field Stop Images

20. LWIR Channel Passbands 50% points estimated by ascertaining wavelength gut ray strikes the left and right edges of detector active area 0% points estimated by finding wavelength for with ray moves from the left edge to right edge and vice versa The values given for Band L4 need to be moved slightly longer because the spatial gap between L3 and L4 recently had to be increased from 13µm to 19µm to accommodate the capabilities of the detector fabrication process 20 Band0%50%100%50%0%Width at 50%Width at 0% label(µm) L16.4596.5896.7156.8426.9720.2530.513 L27.0657.1957.3257.4557.5860.2600.521 L38.0178.1478.2808.4118.5410.2640.524 L48.2878.4178.5508.6818.8110.2640.524 L59.4689.5999.7309.8619.9920.2620.524 L69.93910.07010.20010.33110.4620.2610.523 L710.76910.90011.03011.1611.2910.2600.522 L811.76011.89112.02012.14912.2800.2580.520 L912.34212.47312.60012.72812.8590.2550.517 L1013.07213.20413.33513.46713.5980.2630.526 L1113.37613.50713.63513.76613.8970.2590.521 L1213.67413.80513.93514.05814.1890.2530.515

21. LWIR Detector Array Layout 21

22. FPA Mother Board 22

23. LWIR Detector Package Solid Model Order Sorting Filter 1 6.565µm -10.450µm passband Order Sorting Filter 2 10.780µm -14.085µm passband L1 detector L12 detector

24. LWIR Detector Package Drawing L6 L7 Drawing dimensions are in inches Connector mounted on circuit board 0.250 mm space between filter and detectors

25. LWIR Order-Sorting Filter Two bandpass filters on a monolithic Germanium substrate No uncoated areas except at edges Filter 1 and Filter 2 coatings overlap in 0.240 mm wide transition region Filter 1 Transmittance: ≥ 80% average 6.565 µm - 10.450 µm ≥ 72% absolute 6.565 µm - 10.450 µm ≤ 0.1% absolute UV – 5.85 µm ≤ 0.1% absolute 11.6 µm – 18 µm Filter 2 Transmittance: ≥ 80% average 10.780 µm – 14.085 µm ≥ 72% absolute 10.780 µm – 14.085 µm ≤ 0.1% absolute UV – 9.45 µm ≤ 0.1% absolute 15.45 µm – 18 µm 25 Drawing dimensions in millimeters (mm) 0.240 mm wide region where Filter 1 and Filter 2 coatings overlap Diffraction orders greater than 1 are blocked: Wavelengths > 5.85 µm in diffraction orders > 1 are dispersed to the right of Filter 1. (2*5.85 = 11.7) Wavelengths > 9.45 µm in diffraction orders > 1 are dispersed to the right of Filter 2. (2* 9.45 = 18.9)

26. Zero-Order Diffraction is Blocked by LWIR Lens 26

27. Spacer Between the First Two Lens Elements of LWIR Lens Painted To Minimize Scattered Light From Zero-Order 27 SpacerLens 1Lens 2 Zero-Order Rays

28. Mirrors Substrates: 6061-T6 Aluminum Machining, stress-relieving, and thermal cycling to be done by SDL Diamond turning, post-polishing, lapping and coating to be provided by NU-TEK Optical Surface Coating: Protected Gold Reflectance ≥ 97.5% @3.6 µm to 14.1 µm and 22.5º AOI Flatness ≤ λ/4 @ 633 nm Surface Roughness ≤ 250 Angstroms Mounting Pads Lapped or Diamond Turned 3 Identical Fold Mirrors Diameter 1.307 inches Clear Aperture 1.246 inches 1 Grating Replacement Mirror Diameter 1.417 inches Clear Aperture 1.279 inches 28 Fold Mirrors MWIR Grating Replacement Mirror Drawing Dimensions in inches

29. New Port 3 Dichroic Beamsplitter New Port 3 Beamsplitter required for new cryogenic mounting inside COB Operational temperature: 80K Substrate: ZnSe Diameter: 38.10 mm Thickness: 6.00 mm Clear Aperture: 34.0 mm Surface Flatness: Before coating: λ/4 @ 633 nm After coating: 2λ power, λ/2 irreg. @633 nm Angle of incidence: 25º Reflectance: ≥ 93% average 3.66µm to 5.552 µm ≥ 83% minimum absolute 3.66µm to 5.552 µm Transmittance: ≥ 80% average 6.56µm to 14.09 µm ≥ 70% minimum absolute 6.56µm to 14.09 µm 29 DSI Design

30. Window Substrate: ZnSe Diameter: 44.00 mm Thickness: 3.00 mm Clear Aperture: 37.0 mm Coated Area: ≥ 41.0 mm Surface Flatness: ≤ λ/4 @ 633 nm Angle of incidence: 30º BAR Coating Surface Reflectance: ≤ 2% avg. 3.6 µm to 14.1 µm ≤ 4% max. 3.6 µm to 14.1 µm 30 BAR Coating Reflectance Curve From ISP Optics

31. Optical Component Status & Drawing Numbers 31

32. 32 “Path Ahead” There is room in COB for this MWIR lens and grating in future Si Ge Filter MWIR Grating Si Ge Prescription: EMAS_Port3_V3e_cold.len