1 / 18

Projection of small angle scattering

Projection of small angle scattering. Stefan Hild For the GEO-team March 2008, ILIAS WG1, Pisa. Overview. Intro: small angle scattering Measurement of the small angle scattering function of a GEO600 core optic Potential coupling paths of small angle scattering

nezs
Télécharger la présentation

Projection of small angle scattering

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Projection of small angle scattering Stefan Hild For the GEO-team March 2008, ILIAS WG1, Pisa

  2. Overview • Intro: small angle scattering • Measurement of the small angle scattering function of a GEO600 core optic • Potential coupling paths of small angle scattering • Projection of the scattered light noise of one of the GEO600 catchers ILIAS WG1 meeting, March 2008, Pisa

  3. How much scattered light is necessary to limit the sensitivity of GEO600 ? 1.5e-19 m/sqrt(Hz) sensitivity [m/sqrt(Hz)] Achieved displacement sensitivity Frequency [Hz] Accurary of the phase readout ILIAS WG1 meeting, March 2008, Pisa

  4. How much scattered light is necessary to limit the sensitivity of GEO600 ? • Assuming angle between EC and  to be 90 deg. • With EC = sqrt(2.7kW) we get EC tiny amount of light ILIAS WG1 meeting, March 2008, Pisa

  5. Small angle scattering in general • The amount of scattered light varies with the mirror. • We are interested in very small angles, for instance  = 0.1m/600m = 1.7mrad • Often the scattering funktion is assumed to be cosine-like Super polished mirror amplitude Sandblasted metal works scattering angle ILIAS WG1 meeting, March 2008, Pisa

  6. Photographs of the north end mirror ILIAS WG1 meeting, March 2008, Pisa

  7. Measurement of the small angle scattering of a GEO test mass • Can measure the light passes next to the mirror (red circle). • We get: • Since the modulation depth is similar to main beam: • Using: • We end up at: ILIAS WG1 meeting, March 2008, Pisa

  8. Two different scattering scenarios • A: Light on the mirror scattered directly into the incoming beam (instead of following the folded arm). • B: Scattered light hitting the metal works around the mirror is scattered back into the interferometer mode. ILIAS WG1 meeting, March 2008, Pisa

  9. Scenario A: Direct back scattering in the folded arms • Direct back scattering from MFn and MFe causes 1200m pathlength difference => increased frequency noise coupling (be covered by noise projection) • The position of MFn and MFe is only controlled with low bandwidth (0.1 Hz). MFe and MFn movement in combination with small angle scattering can cause noise in detection band. ILIAS WG1 meeting, March 2008, Pisa

  10. interferometer with „dual recycling“ modecleaner 12W Laser detector Slide stolen from Haralds talk at the LSC meeting Oct 2008 ILIAS WG1 meeting, March 2008, Pisa

  11. Scenario B: Light scattered back from the catchers. • Catchers are not isolated from ground motion. • If we know: • Scattering function of the mirror and catcher • The movement of the catcher • We can do a simple projection. ILIAS WG1 meeting, March 2008, Pisa

  12. The scattering processes required • All together 3 scattering processes are required: • light needs to be scattered onto the catcher. • light at the catcher needs to be scattered back onto a mirror (MCn). • at MCn the light needs to be scattered back into the interferometer mode ILIAS WG1 meeting, March 2008, Pisa

  13. Projection: Step 1 Light power at catcher (90mW) Effective mode diameter (from W. Winkler PhD thesis) ILIAS WG1 meeting, March 2008, Pisa

  14. Projection: Step 2 Transforming light power into effective scattering amplitude: EC ILIAS WG1 meeting, March 2008, Pisa

  15. Projection: Step 3 ASD of catcher movement ASD of displacement caused by scattered light from MFn catcher ILIAS WG1 meeting, March 2008, Pisa

  16. Projection: Step 3 ILIAS WG1 meeting, March 2008, Pisa

  17. More Details can be found in: ILIAS WG1 meeting, March 2008, Pisa

  18. E N D

More Related