Status of the ExAO Testbed

1. Status of the ExAO Testbed Julia Wilhelmsen LLNL/LAO

2. Acknowledgements Gary Sommargren, Lisa Poyneer, Bruce Macintosh, Daren Dillon, Scott Severson, Don Gavel, David Palmer, Nella Barrera

3. The LAO at UCSC We moved!

4. Layout of the Testbed Features • PSDI for built in metrology • Simple optical design for low wavefront error • Shaped pupils for producing regions of high contrast in the image plane PSDI Front End Lens and Aperture Stop Short temporal coherence laser Half-wave retardation plate Variable neutral density filter aperture Variable delay path Optical MEMS Device Polarizers Optical fibers Pinhole Aligner Testbed Area Polarization beam splitter Quarter-wave retardation plates Interferometer CCD camera Piezoelectric phase shifter Image CCD replaces pinhole aligner for Far-Field mode. Computer system

5. Inside the enclosure

6. Stability of Testbed Work by Nella Berrara

7. Normalized unsaturated core Semi-saturated core Bleeding from nearby saturated pixels Dark region behind focal mask (noise floor of camera) Region of 10-7 Contrast Normalized unsaturated core Semi-saturated core Bleeding from nearby saturated pixels Dark region behind focal mask (noise floor of camera) Region of 10-7 Contrast Contrast with Flat

8. The MEMS Deformable Mirror • We have received 4 devices from BM to date • Each device is 10 mm on a side • 1024 -300µm actuators • About 1-1.5 µm stroke with 160 volts • Approx 10 dead actuators per device • 13 bit electronics (4-288 channel boards from Red Nun)

9. Superposition Tests run by Lisa Poyneer at LLNL indicate that superposition works well for estimating MEMS shape.

10. Engineering Lessons • Humidity sensitive • Correct mapping • Dead actuator locations

11. Humidity Sensitivity Oxidation caused by a combination of high voltage and high humidity = dead actuators

12. Solution to humidity • Controlled environment (not as easy as we thought) to below 50% humidity • MEMS device with window • In experiments to date the window has not been a problem

13. Mapping/types of dead actuators • Mapping has been corrected • 188 mis-mapped actuators • Approx. factor of 2 improvement in Flattening • Three types of bad actuators • Dead Actuators that do not move • No response actuators that are not actively moved but “float” with their neighbors • Coupled adjacent actuators that move together

14. Closed Loop Operation IDL Calibrate alignment Calibrate voltage response Directs data acquisition Directs back propagation Calculates wavefront error Calculates actuator voltages Commands MEMS driver Lickdata acquisition Stitchback propagation MEMS Driver

15. Before and after wavefronts Wavefronts taken before and after flattening on Oct 18 162.50 nm RMS total wavefront error 6.13 nm RMS total2.66 nm RMS within control radius

16. Before and after power spectra

17. Simulated Far Fields with MEMS

18. Improving Contrast • Contrast improves by • Number of Actuators2 • Larger aperture covers more of the MEMS • Currently limited by dead actuators on the mems • Wavefront error2 • Correct mapping improved WFE by factor of 2 translates to factor of 4 in contrast • Wavelength2 • Testbed operates in the visible, final instrument will be IR- factor of 10 in contrast

19. Actual far field data with MEMS • Old result at 10-4 • Attempted to take far field data Tuesday but having trouble with consistency of the MEMS device • Improvement between the two simulated far fields is promising for actual far field data Bleeding in CCD Here is a sample image… not an example of what we can do, but the structure seen in the simulation is evident in the real data.

20. Conclusions and Next Steps • Improved far field data with the MEMS • Improve flattening • Measurement with better MEMS (fewer dead actuators) • Wavefront sensor

21. Discussion?

22. Stitch Numerical Back Propagation

23. No response actuators

24. Mapping

25. Influence function