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<<TableOfContents([2])>>
= Arm Length Stabilization by injecting green laser beams from the arm ends =
== Plan ==
=== time line ===
 * [[Upgrade 09/GreenLock/timeline|time line]] describes where we are now and where we go.
=== 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]		 ## page was renamed from Upgrade 09/GreenLock
<<Anchor(TOP)>>
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=== Detailed design ===
 * '''Design and Purchasing Lists'''
  * Optical design / [[Upgrade 09/Purchase List/Green_Locking|item list]]
  * Electronics / control design / [[Upgrade 09/Purchase List/Green_Locking|item list]]
  * [[Upgrade 09/Purchase List/Green_Locking|Purchase list]]
 * '''Detailed considerations'''
  * Optical Layout ([attachment:green_optics.png Table]/ In-vac)
   * [[Upgrade 09/GreenLock/end_table|ETM / end table]] <<ImageLink(endtable.jpg,Upgrade 09/GreenLock/end_table)>>
   * [[Upgrade_09/Optical_Layout#wedge|ITM wedge effect]]
   * [[Upgrade_09/Optical_Layout|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)] 		   . attachment:god_of_green.png
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    . [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)]
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  * Main optics specs (review)
  * Mode matching
  * Green generation
    . manual for the covesion oven
  * Expected performance / noise / control system range
  * Digital servo / operation
  * Alignment (initial / fine / automatic)
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==== Green Preliminary Design: ETM region ====
attachment:green_ETM_preliminary_design.png
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==== Green Preliminary Design: Vertex region ====
attachment:green_vertex_preliminary_design.png		 = Overview =
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=== Development roadmap ===
 * '''End table arrangement'''
  * NPRO placement / optical assembly at the end		  The diagrams below show a conceptual design of the green locking technique
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  * SHG at the end table
  * Control system placement
  * Coarse alignment to the cavity
  * Fine alignment
  * 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		    <<ImageLink(green_vertex_preliminary_design.png,Upgrade 09/GreenLock/Preliminary design for the vertex,height=200)>>
   <<ImageLink(green_ETM_preliminary_design.png,Upgrade 09/GreenLock/Preliminary design for the end,height=200)>>
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  * Relative f_noise between the PSL green and the Arm transmitted green
  * ALS performance
 * '''Sophistication of the scheme'''
  * Automatic handing off scripts		 = Plans =
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  * Ready-to-go panels for AdvLIGO
  * Automatic alignment of the green beam
  * ---
  * Green Michelson for precise ETM calibration		  || ''' long term plans ''' || ''' action item list ''' || [:Advanced_Techniques/Green_Locking/action_item_list] ||
 ||<|3> ''' past plans ''' ||''' October 2010''' || [:Advanced_Techniques/Green_Locking/October_2010] ||
 || ''' November 2010 '''||[:Advanced_Techniques/Green_Locking/November_2010] ||
 ||'''January 2011''' || [:Advanced_Techniques/Green_Locking/January_2011] ||
[[BR]]
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  * Absolute length / mode spacing measurement by green''' ''' = Developer's page =
 ||<:> ''''' Category ''''' ||<:> ''''' Links ''''' ||
 ||''' Optical Layout '''|| (1) [attachment:green_optics.png Table layout] (2) [[Optical_Layout|In-vac layout]] ||
 || ''' Pictures of End tables ''' || (1) [[ETMY_table|Picture of ETMY table]] (2) [[ETMX_table|Picture of ETMX table]]||
 || ''' Lasers ''' || [[Advanced_Techniques/Green_Locking/Lasers|Lasers (specs, temp settings, etc.)]] ||
 || ''' Optics ''' || (1) [[Optical Layout#wedge|ITM wedge effect]] (2) [[Upgrade_09/Optics/RTmeasurement|Mirror RT measurement]]||
 || ''' Mode matching ''' || ([attachment:modematch_END.png mode matching at end table]) ||
 || ''' Electronics ''' || [:Advanced_Techniques/Green_Locking/Electronics]||
 || ''' SHG ''' || [:Advanced_Techniques/Green_Locking/SHG] ||
 || ''' Servos ''' ||[[Advanced_Techniques/Green_Locking/Servos|Servos]] ||
 || ''' Performance ''' ||[[Advanced_Techniques/Green_Locking/Noise Requirement|Noise Requirement]] ||
 || ''' Purchase list ''' || [:Upgrade 09/Purchase List/Green Locking] ||
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----
 . attachment:greenskeleton.jpg
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== Noise Requirement ==
I'd say the arm cavity length should not change more than 1/100 of the resonance width in the time scale of 10sec.[[BR]] For this to be fulfilled, the RMS fluctuation of the cavity length must be suppressed below 1e-11m level.[[BR]] ''Does this make sense ?''		 = Links =
 || ''' aLIGO ALS wiki ''' || http://ilog.ligo-wa.caltech.edu:7285/advligo/Arm_Length_Stabilisation ||
 || ''' Servo modeling (!SimLink) ''' || https://nodus.ligo.caltech.edu:30889/svn/trunk/docs/upgrade08/Green_Locking/Servo_modeling/ ||
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=== Noise Sources ===
==== PLL phase noise ====
==== Phase noise from the cavity common mode motion ====
When the cavity is locked to the green laser, the differential motion of the two mirrors will be suppressed by the servo.[[BR]] However, the common motion of the cavity mirrors will not be suppressed. This common motion will show up as phase noises [[BR]] of the lasers. The time derivative of phase noise is equivalent to frequency noise. The equivalent displacement noise seen [[BR]] by the cavity is dL=(w*x*L)/c, where w is the angular frequency, x is the displacement noise spectrum of the common motion, [[BR]] L is the length of the cavity and c is the speed of light (see [attachment:PhaseNoise.pdf attachment:PhaseNoise.pdf] for derivation).

attachment:Cavity-Common-Diff.png

The two lasers (PSL and green) see the same motion of the cavity but from the opposite sides. Hence, the effect of this phase [[BR]] noise to the two error signals of the green and the PSL lasers will be 180 deg. out of phase. The feedback from the green laser to [[BR]] the cavity length will, therefore, create a noise for the PSL laser.

In order to estimate the contribution of this noise to the green lock, I plotted the estimated phase noise in the following figure.[[BR]] attachment:PhaseNoise.png

I first took a spectrum of ETMX OSEM pos signal to see the motion of the mirror with damping.[[BR]] The blue curve in the figure shows the calibrated OSEM spectrum using the well known 2V/mm OSEM [[BR]] calibration and the whitening filter shape (3Hz zero, 30Hz and 100Hz pole).[[BR]] However, OSEM signal is not a good measure of the seismic noise below the pendulum resonant frequency[[BR]] because the suspension cage and the mirror move together at low frequencies.[[BR]] As a tentative solution, I put a filter to make the spectrum look like 1/f^2 below 0.8Hz.[[BR]] This is diffinitely a hacky solution, and should be replaced with a correctly measured [[BR]] seismic spectrum.

The estimated seismic motion was converted to the phase noise using the above formula.[[BR]] The RMS displacement noise above 0.1Hz is about 3e-12 m, which satisfies the requirement for [[BR]] the green lock stability (1e-11m).		 = Documents =
 ||<:> ''''' Title ''''' ||<:> ''''' Locations ''''' || ''''' Notes ''''' ||
 || ''' The 40m interferometer : prototyping aLIGO locking scheme ''' || [https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=67127 G1100820-v1] || - ||
 || ''' Description of the optical / servo configuration ''' || [https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=6888 DCC?] || - ||
 || ''' Arm Length Stabilization at the 40m prototype ''' || [https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=39965 G1100301-v1]|| - ||
 || ''' ALS at the 40m ''' || [https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=38604 G1100127-v2] || - ||
 || ''' Arm Length Stabilisation for Advanced LIGO ''' || [https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=14040 G1000735-v1] || Experiment done by ANU team ||
 || ''' Arm Length Stabilization for Advanced GW Detectors '''|| [https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=3134 G0900577-v3] || - ||
 || ''' Arm Length Stabilization VCO Noise requirements ''' || [https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=13520 G1000703-v2] || - ||
 || ''' Arm Length Stabilization (ALS): The Plan for Testing at The 40m ''' || [https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=10002 G1000293-v1] || - ||
 || ''' Advanced LIGO Arm Length Stabilization ''' || [https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=1331 G0900215-v1] ||
 || ''' Lock acquisition study for Advanced LIGO''' || [https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=12173 T1000294-v1] || - ||
 || ''' Adv. LIGO Arm Length Stabilisation Design ''' || [https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=1625 T0900144-v4] || -||
 || ''' Adv. LIGO Arm Cavity Pre-Lock Acquisition System ''' || [https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=27983 T080139-x0] || comparison with other techniques ||

  • attachment:god_of_green.png

Overview

  • The diagrams below show a conceptual design of the green locking technique

    • green_vertex_preliminary_design.png green_ETM_preliminary_design.png

Plans

  • long term plans

    action item list

    [:Advanced_Techniques/Green_Locking/action_item_list]

    past plans

    October 2010

    [:Advanced_Techniques/Green_Locking/October_2010]

    November 2010

    [:Advanced_Techniques/Green_Locking/November_2010]

    January 2011

    [:Advanced_Techniques/Green_Locking/January_2011]

BR

Developer's page

Links

Documents

Advanced_Techniques/Green_Locking (last edited 2015-06-23 03:44:00 by EricquinteroATligoDOTorg)