Wind Lidar Working GroupOxnard, CA Feb 2003

Ultraviolet and Multiplexed HOEs: Current

Performance and Future Prospects

Geary Schwemmer, NASA/GSFC

Sangwoo Lee, SSAIRichard Rallison, Ralcon, Inc.

Wind Lidar Working GroupOxnard, CA Feb 2003

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

Wind Lidar Working GroupOxnard, CA Feb 2003

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.

Wind Lidar Working GroupOxnard, CA Feb 2003

UV SHADOE focal spots1 m focal length, 5 FOVs

85 µm diameter

Wind Lidar Working GroupOxnard, CA Feb 2003

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.

Wind Lidar Working GroupOxnard, CA Feb 2003

Reducing Cross-talk

7 µm film 12 µm film

Wind Lidar Working GroupOxnard, CA Feb 2003

Multiplexed Progress-Shared Aperture Diffractive Optical Element (SHADOE)

• UV 5-mux’ed 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.

Wind Lidar Working GroupOxnard, CA Feb 2003

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.