Acknowledging contributions by others to the TWiLiTE Scanning Holographic Telescope Team:

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Acknowledging contributions by others to the
TWiLiTE Scanning Holographic Telescope Team
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 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

• 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

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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

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Heritage HOE Telescope Development
PHASERS refl. HOE, 532 nm 1995/1999
HARLIE trans. HOE 1064 nm, 1998
Geary Schwemmer et al.
SDLs 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

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TWiLiTE Telescope
Design Concept
SDL Optics Laboratory, December 2007
TWiLiTE telescope delivered to NASA-Goddard
December 14, 2007
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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 lt 1 sec
• Provide pointing knowledge to 1 mrad
• Scan motor encoder backlash 1 mrad
• Throughput to Doppler RCVR
• Aperture efficiency gt 296 cm2
• Automatic bore sight ( 40 urad)
• Detector beam steering mirror (AAS system)
• AAS boresight specifications

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Automatic Boresight Alignment
Design goals
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Drive Design for HOE Rotation

• Requirements
• Step size and time Turn HOE 90 deg in 1 second
• Velocity error budget for azimuth angle lt 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 81

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Telescope Optical Design
Secondary (flat)
Tertiary
HOE
Receiver Fiber
Beam Splitter

• Advance in HOE technology
• UV operation at 355 nm

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Displacement Analysis for Optical Elements

• Displacements Due to
• Thermal 20 /-5C
• Vibration
• Critical Optics
• Tertiary Mirror
• Secondary Mirror

Summary Mechanical displacements are within
optical tolerances
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Focal Length, Diffraction Angle and Efficiency
Focal Length 998.2 mm Diffraction Angle 44.86
degrees
HOE 1 Throughput 60 Fraction of energy
(200 ?m spot) 59 Estimated size 340 ?m
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Throughput Link Budget
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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)

1 range bin 250 meters (range gate 1.67 ?sec)

• 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 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
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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
TWiLiTE sensors (requirement ? 40
?rad) Alignment settling time 0.6 seconds
(requirement 1 sec) Pointing accuracy lt 650
?rad, SD 250 ?rad (res.160 ?rad) (requirement
1000 ?rad) FOV (TWiLiTE) 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
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Backup Slides on TWiLiTE Telescope
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TWiLiTE System Block Diagram
Power Dist/Sw
DOPPLER RECEIVER
INS/GPS Data
PRESSURE VESSEL
ETALON
ETALON SPACING/PARALLELISM
Etalon Control
ANALOG/PHOTON COUNTS, SYS DATA
Data Acq.
SIGNAL FIBER
SYNC
Timing/Control
AFT OPTICS
Computer
PRESSURE VESSEL
Scanning Telescope
Laser Cooling
Laser
Laser Power
RECEIVER TEMP CONTROL
INS/GPS
Scanner Ctrl
HOE
PRESSURE VESSEL
Window
Det. Box Temp
PRESSURE VESSEL
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TWiLiTE Telescope Requirements to meet System
Measurement Goals
Mechanical
Optical
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TWiLITE Shot Noise Limited Velocity Error
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Solar Irradiance at the Top of Earths Atmosphere
Source Kitt Peak National Solar Observatory
ftp//nsokp.nso.edu/pub/atlas/
HOEDiffracted UV light
Undiffracted visible light
400 nm
300 nm
355 nm 160 ?W/cm2-nm
Wavelength of laser and interference
filter ??Filter 0.15 or 0.25 nm blocking 10-6
otherwise
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Principal Wavelength Bands of Upward Scattered
Sunlight
Fiber
Fiber
Diam. 200 ?m FOV 440 mrad Afiber 0.00031 cm2
Diam. 200 ?m FOV 200 ?rad A tel 786 cm2
AAS
pickoff mirror (1.5 )
AAS
HOE
Undiffracted light (400 700 nm)
Diffracted light (300 400 nm)
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Optical Design
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Alignment Secondary, Tertiary, Periscope
Diffraction angle alignment
O-ring mount
Diffraction plane alignment
Translation adjustment
Tilt adjustment
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Mechanical Interface
Top Plate
Center of Laser
Metering rods (3)
3.00
2.49
Mounting Points (3)
0.30
HOE Mount Structure
HOE Face
Envelope Dimensions 25 Height 30 Diameter
(includes mounts and motor, 25 without)
Telescope Mass 46kg (101lb)
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HOE and Bearing Mount
Telescope Base Ring
Bearing Sprocket Interface
Sprocket
Bearing
HOE
Tab
HOE Ring