LIGO Document T0900144-v6
- The design of the arm length fluctuation system. This system aids in the lock acquisition of the interferometer by stabilising the arm cavity length fluctuations to within ~1.3 nm.
- Added the following comments in 'Version History -v6'
- updated the introduction
- added more supporting documents
- Updated ’Requirements’. Added ’The ALS will provide a maximum differential arm length error of 10 Hz/rtHz the ALS provides the ability to control the PSL frequency to tune the DC offset with respect to the common arm length., and stated to provide a stability to a ’tenth’ of the arm cavity line width at 1064nm.
- updated ’Mirror Coating Modifications’
- In ’End Station Phase Stabilisation’ added link to the ALS fiber distribution and updated the use of a CMB instead of a TTFSS for the phase locked loop in the end- station.
- In ’Arm locking at 532 nm’ modified the PDH locking bandwidth to say ’5-10 kHz’, and state that we have a minimum green laser power requirement of 20 mW (last paragraph).
- renamed ’Beam Steering’ to ’Beam Steering and Wavefront Sensing’. Clarified the use go the DC QPDs and added a footnote wrt use of a WFS to stabilise the beam motion on the ITM.
- In ’Beam Interception’ added a footnote stating ’The Hartmann wavefront sensor at the end-stations are currently not in use’. Also added links to the mirrored periscope designs on the ISCTEX/Y tables.
- Cleaned up ’Vertex heterodyne measurements’ a little, and stated ’A detailed descrip- tion of the heterodyne implementation is found in Arm Length Stabilization (ALS) Vertex Detection System, T1400317’ twice.
- in ’Lock Acquisition Procedure’ modified the residual arm length fluctuations to not exceed 0.13 nm rms. This is obtained in figure 1, with TM current and force limits seen in figure 8.
- Moved ’Single Arm Test at LHO’ in to the appendix.
- removed ’Draft’
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