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LISA Autocollimator

LISA Autocollimator. Jenna Walrath 8/19/09. Laser Interferometer Space Antenna (LISA). Mission Will detect gravitational waves within a frequency range from 0.03 mHz to above 0.1 Hz Structure Three spacecraft in equilateral triangle with 5 million km sides.

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LISA Autocollimator

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  1. LISA Autocollimator Jenna Walrath 8/19/09

  2. Laser Interferometer Space Antenna (LISA) • Mission • Will detect gravitational waves within a frequency range from 0.03 mHz to above 0.1 Hz • Structure • Three spacecraft in equilateral triangle with 5 million km sides

  3. Laser Interferometer Space Antenna (LISA) http://www.nasa.gov/centers/goddard/images/content/181573main_lisa_LO.jpg

  4. What is an autocollimator? • Optical device for measuring angles • Basic idea is to image something on a camera and measure the deflections of the image Laser Beam splitter CCD or other readout device Lens Mirror

  5. Specifications • Dynamic range of 1° • Noise level of 1nrad/√Hz • Work at a distance of 1m

  6. Initial Design Goal • Instead of point source of light, use a grating • Instead of imaging just one grating, image three—two stationary reference patterns and one dynamic pattern

  7. The Plan LED w/ diffuser Top View Grating CCD Camera Mirror Beamsplitter Lens Two Beamsplitters

  8. Humble Beginnings Side View (sort of) Paper Diffuser Grating Red LED Lens w/ aperture CCD Camera Mirror

  9. Humble Beginnings 6/23/09 High-tech light-shielding device Mirror Light with diffuser and grating Lens with aperture Camera

  10. Improvements to the Plan • double black line in the grating • converging lens between the LED and the grating • Allowed us to get rid of the diffuser • Switched from red (627nm) LED to green (530nm) LED • Encased the whole thing in Styrofoam • Instead of 3 images, just use 1 reference pattern and 1 dynamic pattern (so only one beamsplitter at the end rather than two)

  11. Current Design Green LED light source Auxiliary lens 40R/60T Beamsplitter Grating w/ 135 μm slits Mirror CCD Camera 450mm Planar-Convex Lens 50R/50T Beamsplitter

  12. 8/16/09 High-tech light-shielding device LED 40R/60T beam splitter Auxiliary Lens Grating Camera 50R/50T beam splitter Main Lens Mirror

  13. 8/11/09

  14. Computer Interface Main Pattern Reference Pattern Double black line

  15. Current Status • Dynamic range • We can move our pattern across the length of the camera (3648 pixels) • only limited by the size of the pattern • about 25 peaks in each pattern • Operating distance • still able to get a clear pattern at 1m • The mount was so unstable though, the noise was useless to measure

  16. 8/12/09

  17. Noise

  18. Noise • We have shown that some of our noise is coming from fluctuations in the magnification of the image • Possible causes: • Most likely the expansion and contraction of our grating, which is composed of thin plastic • Vibrations might be causing tiny physical movements of the optical components

  19. Next steps/Improvements • Test photomask grating • Stabilize mirror and beam splitter mounts • Find the best way to take advantage of the reference pattern in the data analysis Photomask AutoCAD drawing with test patterns

  20. In the long run • Make the setup more compact • Folding the beam path • Finding the ideal size for the main lens—as small as possible without sacrificing the quality of the image • Design stable mounting structure and housing for the device • While it’s being designed for LISA, its low noise level and large dynamic range make it useful for a variety of applications

  21. Acknowledgements • I’d like to thank • my advisors, Jens Gundlach and Stephan Schlamminger, as well as everyone at CENPA • The REU directors, Wick Haxton, Warren Buck, and Deep Gupta, as well as Janine Nemerever and Linda Vilett for providing such a great REU experience

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