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| <<TableOfContents([2])>> = Arm length stabilization injecting green laser from the end of the arm = |
= Arm Length Stabilization by injecting green laser beams from the arm ends = <<TableOfContents([2])>>aLIGO ALS wiki http://ilog.ligo-wa.caltech.edu:7285/advligo/Arm_Length_Stabilisation ------- ------- |
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| === '''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] |
=== time line === * [[Upgrade 09/GreenLock/timeline|time line]] describes where we are now and where we go. |
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| * '''Detailed design''' * Optical design / item list |
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| * Electronics / control design / item list | === 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] |
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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]] |
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| * Optical Layout (Table / In-vac) * Mode matching * Main optics specs |
* 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]) |
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| . [attachment:manual_oven.pdf manual for the covesion oven] | |
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| * Digital servo / operation * Alignment (initial / fine / automatic) |
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| * Digital servo / operation | ==== Green Preliminary Design: ETM region ==== attachment:green_ETM_preliminary_design.png |
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| * Alignment (initial / fine / automatic) * '''Development roadmap ''' * '''At the end table arrangement''' * NPRO placement / optical assembly at the end |
==== Green Preliminary Design: Vertex region ==== attachment:green_vertex_preliminary_design.png |
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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 |
=== Development roadmap === * '''End table arrangement''' * NPRO placement / optical assembly at the end |
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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 |
* 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 |
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| * Ready-to-go panels for AdvLIGO * Automatic alignment of the green beam * . * Green Michelson for precise ETM calibration |
* Relative f_noise between the PSL green and the Arm transmitted green * ALS performance * '''Sophistication of the scheme''' * Automatic handing off scripts |
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| * Absolute length / mode spacing measurement by green''' ''' | * 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''' ''' |
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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 ? |
== 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]. |
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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). |
|| '''Laser''' || '''df/dT''' || '''df/dV - within a mode''' || '''df/dV - average''' || || Lightwave || 2.8MHz/mK || 5GHz/V || 1.6GHz/V || || Innolight || 3.3MHz/mK || || || |
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| attachment:Cavity-Common-Diff.png | |
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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. | ==== Lightwave laser ==== attachment:lightwave_temperature_sweep.png |
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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 | ==== Innolight laser ==== attachment:innolight_temperature_sweep.png |
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| 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]] |
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
Detailed considerations
- Optical Layout ([attachment:green_optics.png Table]/ In-vac)
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)
- Optical Layout ([attachment:green_optics.png Table]/ In-vac)
Green Preliminary Design: ETM region
attachment:green_ETM_preliminary_design.png
Green Preliminary Design: Vertex region
attachment:green_vertex_preliminary_design.png
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