Waves and Interference

1. The slides in this collection are all related and should be useful in preparing a presentation on SIM PlanetQuest. Note, however, that there is some redundancy in the collection to allow users to choose slides best suited to their needs.

2. Waves and Interference With one wavelength (color): With all wavelengths (white light): Constructive Interference Destructive Interference

3. Interferometry and Fringes The Resolution of an interferometer depends only on the separation of the two openings, or telescopes, that admit light. Small Separation Low Resolution Large SeparationHigh Resolution Fringes Fringes

4. What is a Michelson Interferometer? • Light from two collectors (telescopes) is combined optically onto a single detector. • When the two beams have traveled the same distance from the star to the detector, then the two beams interfere constructively. • Pathlength is adjusted to find this maximum brightness condition. • With this knowledge and precise measurements of SIM’s internal geometry, the angle to the target can be calculated. • The process gives only one component of angle precisely. • Two measurements are required with baseline rotated ~90° about the line to the star.

5. Interferometry – The Path to High Resolution Interferometers can combine light from two or more mirrors as if they were pieces of a single large telescope. Albert Michelson used interferometry to extend the capabilities of the then largest telescope in the world on Mt. Wilson in Southern California.

6. Michelson Stellar Interferometry detector • An interferometer combines the light from several small telescopes to yield the angular resolution of a much larger telescope ResolutionSensitivity Telescope l/D µD Interferometer l/B µÖ(2*d*B) Telescope Interferometer Combiner & detector Telescope (d) Telescope (d) diameter (D) baseline (B)

7. Measuring Fringe Positions With an Interferometer detected intensity External path delay x = B sin(q) direction to star q external delay- internal delay 0 Siderostat 1 Baseline Vector Siderostat 2 detector Internal path delay Beam Combiner Delay Line The peak of the interference pattern occurs when the internal path delay equals the external path delay

8. A Michelson Astrometric Interferometer ABC

9. How Does SIM Work?  d = differential delay d = differential delay External path delay B telescope 1 telescope 2 detector detected intensity delay line Internal path delay beam combiner Pathlength control to ~ 10 nm (l/50) required for high fringe visibility. f = fringe position on detector 0 The peak of the interference pattern occurs at zero OPD to star