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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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----
[[Upgrade 09/GreenLock/Noise Requirement|Noise Requirement]]

 . 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]]

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

Detailed design

Green Preliminary Design

green_vertex_preliminary_design.png green_ETM_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

Noise Requirements

jump to Noise Requirement

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