Characterizing Lenslet Arrays for the Keck Adaptive Optics

Characterizing Lenslet Arrays for the Keck Adaptive Optics System Laboratory for Adaptive optics (LAO) UC Santa Cruz Name: Abubakarr Bah Home Institution: Santa Rosa Junior College Advisor: Dr. Don Gavel Mentor: Dr. Renate Kupke

What are Lenslets? • • • Small lenses (50 um- 1 mm) Part of an array. Found in Shack-Hartmann wave front sensors. Lenslet on a Shack-Hartmann wavefront sensor Image taken from http: //www. ctio. noao. edu 2

My Project Information Characterizing Lenslets arrays for the Keck adaptive optics system: • Focal Length • Pitch Measurement • Transmission • Lenslet Optical Figure 3

Focal length setup Pinhole (5 µ) Aperture Lenslet . 633 um CCD Computer f Microscope Diode Objective (10 x) laser Collimated light Hartmann Spots Microscope Objective (50 x) 4

Focal length at a single wavelength (. 633 um) Depth of Focal length focus Meas. (mm) (uncertainty) Array Focal length spec. (mm) A 4. 9 ± 0. 5 4. 95 ± 0. 39 B 3. 1 ± 0. 3 3. 11 ± 0. 17 C 2. 4 ± 0. 2 2. 39 ± 0. 11 5

Focal length set up for different Wavelength. Microscope Objective (50 x) Filter CCD White light Source Microscope Objective (10 x) Computer Lenslet 6

Focal length at diff. wavelength Wavelength Focal length A Focal Length B Focal length C 400 4. 42 2. 90 2. 23 500 4. 81 3. 00 2. 42 600 4. 92 3. 14 2. 35 800 4. 86 3. 02 2. 23 700 4. 60 3. 02 2. 46 7

Pitch Measurements: • Spot Pitch Measurements: - Same as Focal Length Setup - Distance b/w Spots • Pitch Measurements: - LAO's Olympus microscope - 20 Lenslet at a time 8

Focal Spot Pitch Lenslet Focal Spot Pitch Spec (mm) Focal Spot Pitch Meas. (mm) RMS Error A 0. 200 0. 1996 ± 0. 00134 B 0. 200 0. 1995 ± 0. 00088 C 0. 200 0. 1997 ± 0. 00091 9

Pitch Measurements Using the LAO's Olympus microscope Measurements were taking 20 lenslet at time lenslet Up (mm) Down (mm) Right (mm) Left (mm) RMS Error A 4. 0000 3. 9980 4. 0000 ± 0. 0010 B 4. 0000 ± 0. 0000 C 4. 0000 3. 9660 ± 0. 0170 up= towards lenslet III 10 . Right= towards markings

Transmission of the Lenslets: Keck Specification: >97 % EXPERIMENTS: • Used The UCO Lick Optical Shop's spectrophotometer. • Made a simple optical setup 11

Throughput. Filter Lenslet Pin Hole White light Source Photometer 12

Transmission of Lenslet: Max 1. 00 Min 0. 84 13

Lenslets optical Figure: 14

Conclusions: . Focal length and Pitch meet specifications. Transmission meets the specifications within 500 -950 nm. Lenslet has a parabolic shape and steps patterns (surprising observation !) 15

Acknowledgments Dr. Don Gavel Dr. Renate Kupke Sandrine Thomas Daren Dillon Marco Reinig Members of the LAO lab Center for Adaptive Optics (CFAO) This work has been supported by the National Science Foundation Science and Technology Center for Adaptive Optics, managed by the University of California at Santa Cruz under cooperative agreement No. AST - 9876783. " 16