Overview

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

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]

Developer's page

Category	Links
Optical Layout	[attachment:green_optics.png Table] / In-vac
end table	Picture of ETMY table / Picture of ETMX table
Lasers	Lasers (specs, temp settings, etc.)
Optics	ITM wedge effect / 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]
Doubling Oven	[attachment:PV40.pdf drawing of PV40 oven], [attachment:PVP2.pdf drawing of the base plate PVP2], [attachment:manual_oven.pdf manual for the covesion oven]
Performance	Noise Requirement
Purchase list	[:Upgrade 09/Purchase List/Green Locking]

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/

Documents

Title	Locations
Description of the optical / servo configuration	https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=6888
Arm Length Stabilization at the 40m prototype	https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=39965

-  ⇤ ← Revision 10 as of 2009-12-22 23:47:03 → 
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+   ← Revision 141 as of 2011-09-23 06:23:17 → ⇥
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-<<TableOfContents([2])>>
= Arm length stabilization injecting green laser from the end of the arm =
== Plan ==
 * '''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'''
  * Optical design / item list

  * Electronics / control design / item list

 * '''Detailed considerations'''
  * Optical Layout (Table / In-vac)
  * Mode matching
  * Main optics specs
  * Green generation
  * Expected performance / noise / control system range
+   . attachment:god_of_green.png
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-  * Digital servo / operation
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-  * Alignment (initial / fine / automatic)
 * '''Development roadmap
'''
  * '''At the end table arrangement'''
+= Overview =
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-   * 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 (Arm Length Stabilization) 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
+= Plans =
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-   * Absolute length / mode spacing measurement by green'''
'''
+|| ''' 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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-----
== 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 ?
+= Developer's page =
||<:> ''''' Category ''''' ||<:> ''''' Links ''''' ||
||''' Optical Layout '''|| [attachment:green_optics.png Table]  /   [[Optical_Layout|In-vac]] ||
|| ''' end table ''' || [[ETMY_table|Picture of ETMY table]] / [[ETMX_table|Picture of ETMX table]]||
|| ''' Lasers ''' || [[Advanced_Techniques/Green_Locking/Lasers|Lasers (specs, temp settings, etc.)]] ||
|| ''' Optics ''' ||  [[Optical Layout#wedge|ITM wedge effect]] /  [[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] ||
|| ''' Doubling Oven ''' ||  [attachment:PV40.pdf drawing of PV40 oven], [attachment:PVP2.pdf drawing of the base plate PVP2],  [attachment:manual_oven.pdf manual for the covesion oven] ||
|| ''' Performance ''' ||[[Advanced_Techniques/Green_Locking/Noise Requirement|Noise Requirement]] ||
|| ''' Purchase list ''' ||  [:Upgrade 09/Purchase List/Green Locking] ||
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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).
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-attachment:Cavity-Common-Diff.png
+= 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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-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 ''''' ||
|| ''' Description of the optical / servo configuration ''' || https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=6888  ||
|| ''' Arm Length Stabilization at the 40m prototype ''' || https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=39965 ||