Arm Length Stabilization by injecting green laser beams from the arm ends

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• We are developing a technique of Arm Length Stabilization (ASL) for advanced LIGO. The technique employs two auxiliary green lasers at each end of the arm. Basically these lasers are able to sense the displacement of the each arm independently on the main laser, eventually make full lock acquisition of advanced interferometer more robust and reliable.

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aLIGO ALS wiki http://ilog.ligo-wa.caltech.edu:7285/advligo/Arm_Length_Stabilisation

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Plan

time line

• The time line describes where we are now and where we go. time line

Conceptual design

• Description of the optical / servo configuration [https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=6888 LIGO DCC]

• Servo modeling (SimLink) [https://nodus.ligo.caltech.edu:30889/svn/trunk/docs/upgrade08/Green_Locking/Servo_modeling/ 40mSVN]

Green Preliminary Design

Development roadmap

• End table arrangement

  • NPRO placement / optical assembly at the end
  • SHG at the end table
  • Control system placement
  • Coarse/fine alignment to the cavity
  • Lock of the green beam to the cavity

• At the PSL table

  • SHG at the PSL table

• Digital control

  • Virtual Green lock by RCG
  • GPIB interfaces

• Vertex tank optical arrangement

  • In-vac steering (PO transmission / Periscope / Mirrors)
  • Vertex phase noise measurement
    • Electronics placement
    • Control system implementation

• Performance evaluation

  • f_noise of green beam / PDH performance
  • Relative f_noise between the PSL green and the Arm transmitted green
  • ALS performance

• Sophistication of the scheme

  • Automatic handing off scripts
  • Ready-to-go panels for AdvLIGO
  • Automatic alignment of the green beam
  • Green Michelson for precise ETM calibration

  • Absolute length / mode spacing measurement by green

Detailed design

• Design and Purchasing Lists

  • Optical design / item list

  • Electronics / control design / item list

  • Purchase list

• Detailed considerations

  • Optical Layout ([attachment:green_optics.png Table]/ In-vac)

    • ETM / end table

    • ITM wedge effect

    • Periscopes for beam steering from PR3/SR3 transmissions to the PSL viewport

    • PSL viewport modification (viewport cover / tube / PSL box / periscope on the PSL table)
    • PSL table

    • Laser & SHG specs --- power, polarization, Xtals

      • - references

      • [1] G.D.Boyd and D.A. Kleinman, [http://jap.aip.org/japiau/v39/i8/p3597_s1 "Parametric interaction of Focused Gaussian Light Beams", J.A. Phys. 39, 3597 (1968)]

      • [2] C. Zhang, Y.Qin and Y.Zhu, [http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-33-7-720 "Perfect quasi-phase matching for the third-harmonic generation using focused Gaussian beams",Opt. Lett. 33, 720 (2008)]

  • Main optics specs (review)
  • Mode matching ([attachment:modematch_END.png mode matching at end table])
  • Green generation
    • [attachment:manual_oven.pdf manual for the covesion oven]
  • Expected performance / noise / control system range
  • Digital servo / operation
  • Alignment (initial / fine / automatic)

Control information

• jump to Control Information

Noise Requirements

• jump to Noise Requirement