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Automatic Alignment system Improvements after the VSR1 M. Mantovani for the Alignment team

Automatic Alignment system Improvements after the VSR1 M. Mantovani for the Alignment team. Summary. Installation of the galvo system for the terminal bench quadrant diodes (actually we are using only for one WE bench quadrant) Angular control system noise performances

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Automatic Alignment system Improvements after the VSR1 M. Mantovani for the Alignment team

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  1. Automatic Alignment system Improvements after the VSR1 M. Mantovani for the Alignment team

  2. Summary • Installation of the galvo system for the terminal bench quadrant diodes (actually we are using only for one WE bench quadrant) • Angular control system noise performances Optimization of the control filters Improving the sensor electronic noise • Input mirrors angular control Rearranged the end benches optical components and retuned the Gouy phase for the end bench quadrant diodes

  3. Why are the galvo useful? Translation stages: too noisy (centering rate ~4sec)‏ Galvo: bandwidth of tens of Hz The miscentering of the beam on the diode spoils the error signal

  4. Q81 galvo installation

  5. Asymmetry fluctuations at step 12 Beam fluctuations on WE bench Q81 Q81 Galvo on Galvo off Loop unity gain frequency ~ 20Hz

  6. Control Filters optimization improving the high frequency cut off Sensitivity improvement

  7. Control Filters optimization improving the low frequency stability improving the low frequency gain of the differential mode improves the accuracy of the alignment, visible also on the dark fringe

  8. Sensor electronic noise reduction Q81AC to control the BS Q1pAC to control the differential end mode Q21DC to control the common end mode

  9. Sensor electronic noise reduction Starting fro 10 Hz most of the sensors are limited by electronic noise thanks to the new electronics the electronic noise can be reduced

  10. End bench optics rearrangement the quadrant diodes have been placed in the optimum Gouy phase to detect the input mirrors

  11. Input mirrors control • The error signals are able to detect the input mirror angular displacement, but these are strongly affected by the air currents inside the acoustic enclosure. • Thus: • the air currents have to be reduced by improving the insulation of the optical bench (not trivial) • the error signals have to be made insensible to the air flow and to the bench motions by retuning slightly the Gouy phases (not clear if it is feasible) Bench movements Air flow

  12. Conclusions and next steps • The galvos have been installed on the terminal benches, for the moment we are actually using only one of them • The angular control system noise can be reduced below the design sensitivity by acting on the control filter performances, on the electronics and on the mirror/beam centring. • The input mirrors can be controlled by using the terminal quadrants if the low frequency noise on the sensors can be reduced • Improve the beam/mirror centering by using a permanent frequency line excitation on the terminal mirrors

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