Ultraviolet Holographic Telescope for TWi Li TE J

Ultraviolet Holographic Telescope for TWi. Li. TE J. Hancock*, J. Swasey*, A. Shelley*, G. Schwemmer, C. Marx §, S. Schicker*, G. Bowen*, T. Wilkerson* *Space Dynamics Laboratory Logan, UT 84341 § NASA-Goddard space Flight Center Greenbelt, MD 20771 Presentation for the Working Group on Space Based Lidar Winds Monterey, CA February 5 – 8, 2008 Acknowledging contributions by others to the TWi. Li. TE Scanning Holographic Telescope Team: Marc Hammond (SDL & Diffraction Ltd. ) – Consultant & Designer Matthew Mc. Gill (GSFC) – Scientist & Adviser Richard Nelson (SDL) – Designer Quinn Young (SDL) – Thermal Engineering Brent Bos (GSFC) – Optical Engineering, ex-COTR Richard Rallison (Wasatch Photonics) – HOE Consultant Elroy Pearson (Wasatch Photonics) – HOE Consultant

Outline of Presentation • Background of TWi. Li. TE Telescope • Telescope Requirements • Auto-alignment System • HOE Rotary Drive • Optical System • Opto-mechanical Integrity • Properties of First UV HOEs • Solar Background Light • Alignment and Test Results • Backup Information Slides

Heritage: HOE Telescope Development PHASERS refl. HOE, 532 nm 1995/1999 HARLIE trans. HOE 1064 nm, 1998 Geary Schwemmer et al. SDL’s UV Cornerstone HOE 355 nm, (design 2003/2004) • • Receiver: UV HOE (355 nm) 45 -deg off-axis FOV Folded optical path 3 -rod metering structure Rotating HOE (Step/Stare) Coaxial laser transmission via periscope through HOE Designer: Marc Hammond

TWi. Li. TE Telescope SDL Optics Laboratory, December 2007 TWi. Li. TE telescope delivered to NASA-Goddard December 14, 2007 Design Concept

Telescope Functional Requirements • • • Rcvr FOV and laser beam; conical, 45° off-nadir, N-step-stare Integrated rotating HOE and beam steering mirrors – Step Interval 1 – 2 seconds, Alignment settling time < 1 sec Provide pointing knowledge to ± 1 mrad – Scan motor encoder + backlash ≤ 1 mrad Throughput to Doppler RCVR – Aperture * efficiency > 296 cm 2 Automatic bore sight (± 40 urad) – Detector & beam steering mirror (AAS system) – AAS boresight specifications: Parameter Field of View Value 800 µrad Nominal alignment time 1 sec Maximum alignment time 2 sec Feedback control time constant 100 ms

Automatic Boresight Alignment Design goals Auto-alignment FOV 800 urads Telescope FOV 200 urads Focal spot size ~150 urads L 1 BS L 2 Auto-alignment Optics (AAS) HOE Laser Feedback to fast steering mirror

Drive Design for HOE Rotation • • Requirements Step size and time – Turn HOE 90 deg in 1 second Velocity error budget for azimuth angle < 0. 2 m/s 1 mrad Drive System • Motor - Animatics SM 3430 – Encoder – 4000 counts/rev – Low Pressure Grease • Bearing – Kaydon SG 180 XP 0 A – 440 C Stainless Steel • Sprockets and Belt – Gates GT 2 – 176 Tooth Custom Sprocket – 22 Tooth Pulley – 1600 Tooth Belt – Gear Ratio 8: 1 Azimuth Angle Pointing Knowledge • • • Motor Resolution – 0. 20 mrad Pulley Backlash – 0. 62 mrad Sprocket Backlash – 0. 16 mrad • • RSS Total – 0. 67 mrad Sum Total – 0. 98 mrad

Telescope Optical Design Tertiary Secondary (flat) HOE Receiver Fiber Beam Splitter Advance in HOE technology • UV operation at 355 nm

Displacement Analysis for Optical Elements • • Displacements Due to – Thermal 20 +/-5 C – Vibration Critical Optics – Tertiary Mirror – Secondary Mirror Tertiary Mirror Secondary Mirror Axial (μm) Radial (μm) Tilt (μrad) Thermal ± 25 ± 35 ± 40 ± 10 ± 20 Vibration ± 40 ± 25 ± 30 ± 70 ± 94 ± 121 Displacement Total ± 65 ± 60 ± 35 ± 110 ± 104 ± 141 Required Tolerances ± 250 ± 100 ± 349 ± 250 ± 175 Summary: Mechanical displacements are within optical tolerances

Focal Length, Diffraction Angle and Efficiency Focal Length: 998. 2 mm Diffraction Angle: 44. 86 degrees Focal Length HOE # 1: Throughput ~ 60 % Fraction of energy (200 m spot) = 59 % Estimated size ~ 340 m

Throughput Link Budget Parameter CDR Value Basis / Explanation Clear aperture diam. (cm) 38. 8 TWi. Li. TE HOE #1 measurement Effective area (cm 2) 786 (area-obscuration) x cos 45° HOE efficiency 0. 60 Pre-TWILITE Laboratory measurement Boresight and alignment losses 0. 59 TWi. Li. TE HOE #2 measurement Boresight pickoff . 985 Calculation for S/N=10 per pixel Fiber throughput 0. 93 Other optics 0. 96 Total Optical Efficiency 0. 32 Product of optical efficiencies Total throughput (cm 2) 254 Area * Total Optical Efficiency (296 desired) FOV (µrad) 200 µm field stop / 1 m focal length Slew time 1 s Selected motor and gearing Bore sight time 1 s Auto-alignment SNR calculation

Predicted Solar Background Signals for TWi. Li. TE Telescope (Nadir FOV) No solar background contribution below 300 nm: Borofloat glass absorption Visible light (400 – 700 nm) produces background (per shot per bin) at most • 0. 63 photon counts (small fiber) • 2. 52 counts (AAS system) 1 range bin Ultraviolet light (300 – 400 nm) background (per shot per bin): • 1. 0 photon counts (small fiber, narrow filter) • 4. 0 counts (AAS, narrow filter) • 2. 2 counts (small fiber, wide filter) • 8. 9 counts (AAS, wide filter) = 250 meters (range gate =1. 67 sec) Estimated minimum total SNR 14 - 15 for the perfectly aligned AAS signal, integrated over all altitude range bins. Adjusted simulations needed to refine the predictions of SNR as a function of AAS degree of alignment

Succesful Alignment & Test at SDL for Goddard Delivery, December 2007 Mutual alignment of all telescope optics with HOE normal and rotation axis: 10 radians Best spot size (~ 340 m) for HOE # 1 & 2 at 45. 0º, but Diffraction angle for initial, bearing-centered HOE = 45. 9º Small shims and tilt for HOE de-centration: adjusts to 45. 0º Mutual alignment 20 rad between AAS and TWi. Li. TE sensors (requirement: 40 rad) Alignment settling time = 0. 6 seconds (requirement 1 sec) Pointing accuracy < 650 rad, SD = 250 rad (res. 160 rad) (requirement: 1000 rad) FOV (TWi. Li. TE) 320 -380 rad (required 200 rad) Inference: excess due to excess spot size FOV (AAS) ± 800 rad per channel (required 800 rad) Improved performance expected with recent HOE fabrication

Backup Slides on TWi. Li. TE Telescope

TWi. Li. TE System Block Diagram Power Dist/Sw DOPPLER RECEIVER PRESSURE VESSEL ETALON SPACING/PARALLELISM ETALON ANALOG/PHOTON COUNTS, SYS DATA SIGNAL FIBER INS/GPS Laser Cooling Laser Power Scanner Ctrl HOE Window Det. Box Temp PRESSURE VESSEL Computer Scanning Telescope Laser RECEIVER TEMP CONTROL Data Acq. Timing/Control AFT OPTICS PRESSURE VESSEL Etalon Control SYNC PRESSURE VESSEL A/D SIGNAL FIBER WATER POWER INS/GPS Data

TWi. Li. TE Telescope Requirements to meet System Measurement Goals Mechanical Optical Parameter Value Telescope Impact Velocity accuracy (LOS projected) (m/s) 1. 5 Throughput Nadir angle (deg) 45 Throughput Step-stare scan pattern (1 -16 steps) 8 nominal Scanner torque Scan cycle time seconds (km) 112 s (22. 4 km) Scanner torque Horizontal integration per LOS (seconds) & ground track (km) Slew period (s) 10 s (2 km) Throughput & torque 2 - 4 Scanner torque Field Of View 200 µrad Focal spot size, Throughput Pointing knowledge accuracy & precision 900 µrad Scan motor system

TWi. LITE Shot Noise Limited Velocity Error

Solar Irradiance at the Top of Earth’s Atmosphere Source: Kitt Peak National Solar Observatory ftp: //nsokp. nso. edu/pub/atlas/ 300 nm HOE—Diffracted UV light 355 nm 160 W/cm 2 -nm Wavelength of laser and interference filter λFilter = 0. 15 or 0. 25 nm blocking = 10 -6 otherwise 400 nm Undiffracted visible light

Principal Wavelength Bands of Upward Scattered Sunlight Fiber Diam. = 200 m FOV = 200 rad A tel = 786 cm 2 AAS Fiber Diam. = 200 m FOV = 440 mrad Afiber = 0. 00031 cm 2 pickoff mirror (1. 5 %) AAS HOE Diffracted light (300 – 400 nm) Undiffracted light (400 – 700 nm)

Optical Design Radius of Curvature Secondary Diam. Substrate Description Made by Nu-Tek, 0. 5” thick, flat to 2 waves PV, Coated R> 99% flat 8. 5”, 8” CA Pyrex Tertiary 515 mm 3” S Fused Silica CVI Collimator 77. 3 mm 1” Fused Silica CVI Beam Splitter Focus Lens flat wedge 1. 5” Fused Silica CVI, 1 degree wedge, R = 1. 5% front side, R<0. 75 back side 20. 6 mm 1” Fused Silica CVI

Alignment: Secondary, Tertiary, Periscope Diffraction angle alignment O-ring mount Diffraction plane alignment Translation adjustment Tilt adjustment

Mechanical Interface Top Plate Center of Laser 3. 00” 2. 49” 0. 30” HOE Mount Structure Metering rods (3) Mounting Points (3) HOE Face Envelope Dimensions: Telescope Mass: 46 kg (101 lb) 25” Height 30” Diameter (includes mounts and motor, 25” without)

HOE and Bearing Mount Telescope Base Ring Bearing Sprocket Interface Sprocket Bearing HOE Ring Tab