Acknowledging contributions by others to the TWiLiTE Scanning Holographic Telescope Team: Marc Hammond (SDL & Diffraction Ltd.) – Consultant & Designer Matthew McGill (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 Ultraviolet Holographic Telescope for TWiLiTE J. Hancock*, J. Swasey*, A. Shelley*, G. Schwemmer, C. Marx §, S. Schicker*, G. Bowen*, T. Wilkerson* *Space Dynamics Laboratory Logan, UT § NASA-Goddard space Flight Center Greenbelt, MD Presentation for the Working Group on Space Based Lidar Winds Monterey, CA February 5 – 8, 2008

Outline of Presentation Background of TWiLiTE 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 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 SDL’s UV Cornerstone HOE 355 nm, (design 2003/2004) Geary Schwemmer et al.

TWiLiTE Telescope Design ConceptSDL Optics Laboratory, December 2007 TWiLiTE telescope delivered to NASA-Goddard December 14, 2007

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: ParameterValue Field of View800 µrad Nominal alignment time1 sec Maximum alignment time2 sec Feedback control time constant 100 ms

HOE L1BS L2 Auto-alignment Optics (AAS) Laser Feedback to fast steering mirror Auto-alignment FOV 800 urads Telescope FOV 200 urads Focal spot size ~150 urads Automatic Boresight Alignment Design goals

Drive Design for HOE Rotation Requirements Step size and time – Turn HOE 90 deg in 1 second Velocity error budget for azimuth angle < 0.2m/s  1 mrad Drive System Motor - Animatics SM 3430 –Encoder – 4000 counts/rev –Low Pressure Grease Bearing – Kaydon SG180XP0A –440C Stainless Steel Sprockets and Belt – Gates GT2 –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 HOE Receiver Fiber Beam Splitter Advance in HOE technology UV operation at 355 nm Tertiary Secondary (flat)

Displacement Analysis for Optical Elements Displacements Due to –Thermal 20 +/-5C –Vibration Critical Optics –Tertiary Mirror –Secondary Mirror Tertiary MirrorSecondary Mirror Axial (μm) Radial (μm) Tilt (μrad) Axial (μm) Radial (μm) Tilt (μrad) Thermal ±25±35±5±40±10±20 Vibration ±40±25±30±70±94±121 Displacement Total ±65±60±35±110±104±141 Required Tolerances ±250±100±349±250±150±175 Summary: Mechanical displacements are within optical tolerances

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

Throughput Link Budget ParameterCDR ValueBasis / Explanation Clear aperture diam. (cm)38.8TWiLiTE HOE #1 measurement Effective area (cm 2 )786(area-obscuration) x cos 45° HOE efficiency0.60Pre-TWILITE Laboratory measurement Boresight and alignment losses0.59TWiLiTE HOE #2 measurement Boresight pickoff.985Calculation for S/N=10 per pixel Fiber throughput0.93 Other optics0.96 Total Optical Efficiency0.32Product of optical efficiencies Total throughput (cm 2 )254Area * Total Optical Efficiency (296 desired) FOV (µrad) µm field stop / 1m focal length Slew time1 sSelected motor and gearing Bore sight time1 sAuto-alignment SNR calculation

Predicted Solar Background Signals for TWiLiTE 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) 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) Estimated minimum total SNR 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 1 range bin = 250 meters (range gate =1.67  sec)

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 45.0 º, but Diffraction angle for initial, bearing-centered HOE = 45.9 º Small shims and tilt for HOE de-centration: adjusts to 45.0 º Mutual alignment  20  rad between AAS and TWiLiTE 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 (TWiLiTE)  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 TWiLiTE Telescope

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

TWiLiTE Telescope Requirements to meet System Measurement Goals ParameterValueTelescope Impact Velocity accuracy (LOS projected) (m/s)1.5Throughput Nadir angle (deg)45Throughput Step-stare scan pattern (1-16 steps)8 nominalScanner torque Scan cycle time seconds (km)112 s (22.4 km)Scanner torque Horizontal integration per LOS (seconds) & ground track (km) 10 s (2 km)Throughput & torque Slew period (s)2 - 4Scanner torque Field Of View200 µradFocal spot size, Throughput Pointing knowledge accuracy & precision900 µradScan motor system Mechanical Optical

TWiLITE Shot Noise Limited Velocity Error

Solar Irradiance at the Top of Earth’s Atmosphere 355 nm 160  W/cm 2 -nm Source: Kitt Peak National Solar Observatory ftp://nsokp.nso.edu/pub/atlas/ 400 nm 300 nm HOE — Diffracted UV light Undiffracted visible light Wavelength of laser and interference filter  λ Filter = 0.15 or 0.25 nm blocking = otherwise

Diffracted light (300 – 400 nm) Undiffracted light (400 – 700 nm) Fiber Diam. = 200  m FOV = 200  rad A tel = 786 cm 2 Diam. = 200  m FOV = 440 mrad A fiber = cm 2 Fiber AAS Principal Wavelength Bands of Upward Scattered Sunlight HOE pickoff mirror (1.5 %)

Optical Design Radius of Curvature Diam.SubstrateDescription Secondaryflat8.5”, 8” CAPyrex Made by Nu-Tek, 0.5” thick, flat to 2 waves PV, Coated R> 99% Tertiary515 mm3” SFused SilicaCVI Collimator77.3 mm1”Fused SilicaCVI Beam Splitterflat wedge1.5”Fused Silica CVI, 1 degree wedge, R = 1.5% front side, R<0.75 back side Focus Lens20.6 mm1”Fused SilicaCVI

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

Mechanical Interface Envelope Dimensions: 25” Height 30” Diameter (includes mounts and motor, 25” without) Mounting Points (3) Metering rods (3) Top Plate 2.49” 3.00” 0.30” HOE Face Center of Laser HOE Mount Structure Telescope Mass: 46kg (101lb)

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