Differences between revisions 6 and 86 (spanning 80 versions)

Arm Length Stabilization using green laser beams

. attachment:green_man.jpg

We are developing a technique of Arm Length Stabilization (ALS) 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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Designs and Plans

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

Installation status

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
- Electronics
- Digital servo / operation
- Alignment (initial / fine / automatic)
jump to Control Information

-  ⇤ ← Revision 6 as of 2009-08-25 09:31:57 → 
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+   ← Revision 86 as of 2010-07-13 03:16:41 → ⇥
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-= Green Laser Injection for Arm Pre-Lock =
+= Arm Length Stabilization using green laser beams =
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-We plan to install green lasers, which are phase locked to the PSL laser, at each end station to pre-lock the arm cavities before the lock acquisition.
+ <<Anchor(TOP)>>   .   attachment:green_man.jpg
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-== Basic Concept ==
+   . We are developing a technique of Arm Length Stabilization (ALS) 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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-== 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 ?
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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] for derivation).
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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.
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-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
+-------

== Designs and Plans ==
=== time line ===
 * The time line describes where we are now and where we go. B) [[Upgrade 09/GreenLock/timeline|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 ====
   .     <<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)>>



[[BR]]

-------
== Installation status ==

 * '''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)]

    . [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
  *  B) [[Upgrade 09/GreenLock/Electronics|Electronics]]
 
  * Digital servo / operation
  * Alignment (initial / fine / automatic)


 .  B) [[Upgrade 09/GreenLock/Control Information|jump to Control Information]]

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== Links ==
 .  B) [[Upgrade 09/GreenLock/Noise Requirement|jump to Noise Requirement]]

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

 . [#TOP back to the page top]
<<ImageLink(god_of_green.png,#TOP,width=80[,height=90]][,alt=alttag])>>