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| = Green Laser Injection for Arm Pre-Lock = | <<Anchor(TOP)>> = 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. | . attachment:god_of_green.png |
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| == Basic Concept == | |
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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. |
= Conceptual Design = |
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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 |
<<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)>> 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]] Mode matching ([attachment:modematch_END.png mode matching at end table]) Green generation [attachment:manual_oven.pdf manual for the covesion oven] [[Upgrade 09/GreenLock/Electronics|Electronics]] [[Upgrade 09/Purchase List/Green Locking|Purchase list]] [[Upgrade 09/GreenLock/Control Information|jump to Control Information]] [[Upgrade 09/GreenLock/Noise Requirement|jump to Noise Requirement]] = links = || ''' 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] || |
Arm Length Stabilization using green laser beams
- attachment:god_of_green.png
Conceptual Design
- Optical Layout ([attachment:green_optics.png Table]/ In-vac)
ETM / end table
Mode matching ([attachment:modematch_END.png mode matching at end table]) Green generation [attachment:manual_oven.pdf manual for the covesion oven]
ITM wedge effect Purchase list jump to Control Information jump to Noise Requirement
links
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] |