Differences between revisions 53 and 56 (spanning 3 versions)

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

<<TableOfContents: execution failed [Argument "maxdepth" must be an integer value, not "[2]"] (see also the log)>>aLIGO ALS wiki

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

Plan

time line

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]

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)

Green Preliminary Design

Development roadmap

End table arrangement
- NPRO placement / optical assembly at the end
- 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
- 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

Control information

Laser Frequency vs Crystal Temperature

Plots of the laser frequency vs temperature (measured by beating against a second laser) are shown below. [http://nodus.ligo.caltech.edu:8080/40m/2794 Also, see the elog here].

Laser	df/dT	df/dV - within a mode	df/dV - average
Lightwave	2.8MHz/mK	5GHz/V	1.6GHz/V
Innolight	3.3MHz/mK

Lightwave laser

attachment:lightwave_temperature_sweep.png

Innolight laser

attachment:innolight_temperature_sweep.png

Noise Requirements

jump to Noise Requirement

-  ⇤ ← Revision 53 as of 2010-04-23 19:14:22 → 
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-<<TableOfContents([2])>>
= Arm Length Stabilization by injecting green laser beams from the arm ends =
== aLIGO ALS wiki ==
+= Arm Length Stabilization by injecting green laser beams from the arm  ends =
<<TableOfContents([2])>>aLIGO ALS wiki
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-[http://ilog.ligo-wa.caltech.edu:7285/advligo/Arm_Length_Stabilisation]
+http://ilog.ligo-wa.caltech.edu:7285/advligo/Arm_Length_Stabilisation

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-  * 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]]
+  * 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]]
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-   * [[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]]
+   * [[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]]
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-    .  [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)]
+    . [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)]
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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)]
+    . [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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-    .  [attachment:manual_oven.pdf manual for the covesion oven]
+   . [attachment:manual_oven.pdf manual for the covesion oven]
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-==== Green Preliminary Design: ETM region ====
attachment:green_ETM_preliminary_design.png
+==== Green Preliminary Design ====
<<ImageLink(green_vertex_preliminary_design.png,Preliminary design for the end,height=200)>>
<<ImageLink(green_ETM_preliminary_design.png,Preliminary design for the vertex,height=200)>>
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-==== Green Preliminary Design: Vertex region ====
attachment:green_vertex_preliminary_design.png
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-|| Lightwave   ||   2.8MHz/mK ||       5GHz/V  ||  1.6GHz/V ||
|| Innolight   ||   3.3MHz/mK ||    ||   ||
+|| Lightwave ||   2.8MHz/mK ||       5GHz/V ||  1.6GHz/V ||
|| Innolight ||   3.3MHz/mK || || ||
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-----
 . attachment:greenskeleton.jpg   

== 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 ?''

=== 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).
+= Noise Requirements =
[[Upgrade 09/GreenLock/Noise Requirement|jump to Noise Requirement]]