Wind Lidar Working Group

1
Ultraviolet and Multiplexed HOEs Current
Performance and Future Prospects

• Geary Schwemmer, NASA/GSFC
• Sangwoo Lee, SSAI
• Richard Rallison, Ralcon, Inc.

2
Rotating HOE and SHADOE Concepts
U. S. Patent No. 6,479,808 B1 Nov. 12, 2002
U.S. Patent No. 5,255,065 Oct. 19, 1993
3
Improved UV performance

• Smaller spots 130 µrad for 40 cm diameter 70
  µrad for 20 cm diameter. (Spots containing 85 of
  diffracted energy)
• Greater efficiency 58 for 40 cm diameter, after
  10 lost to Fresnel reflections.

4
UV SHADOE focal spots1 m focal length, 5 FOVs
85 µm diameter
5
Remaining Issues

• Loss Mechanisms
• Scattered Light and Cross-Talk 10
• Zero-order 10
• Absorption 10
• Solutions
• Reduce scattered light by increasing refractive
  index.
• Reduce cross-talk and zero order using thicker
  films (16 microns), decreasing index modulation,
  and increasing incident and diffraction angles.
• Tradeoff between absorption and increased
  diffraction.
• Investigate alternate diffractive technologies
  for higher efficiency
• High-power laser beam-steering solutions using
  refractive optics.

6
Reducing Cross-talk
12 µm film
7 µm film
7
Multiplexed Progress-Shared Aperture Diffractive
Optical Element (SHADOE)

• UV 5-muxed HOEs being made with small spots
  (70µm)
• 1st-order diffraction efficiency 60
• Improvements in processing and design expected to
  improve efficiency to 85, based on recent
  experimental results.

8
Future Prospects

• Improved UV SHADOE in the lab undergoing testing
  (?80).
• 40 cm UV HOE for Direct Detection Doppler Lidar
  this year.
• Designs for large aperture (10-20 m2) mosaic HOE
  telescope contemplated for Mars Optical Comm.