04. November 2004 A. Freise A. Freise, M. Loupias Collaboration Meeting November 04, 2004 Alignment Status

04. November 2004 A. Freise Overview Suspended bench External bench Output Mode-Cleaner Pre-alignment Non-linear alignment Linear alignment Drift control Simulation Hardware

04. November 2004 A. Freise Pre-Alignment Suspended bench External bench Output Mode-Cleaner Interferometer pre-aligned since more than one year Nevertheless, some pre-alignment is always necessary: re-alignment of a single component after an intervention: Procedure as in the beginning. Difficult with low light power (10% input light) but it was already successfully done for the input beam alignment (including automatic beam matching) manual re-alignment after a long period without (global) control: procedures exist for the recombined IFO and are currently being developed by the detector operation / locking groups

04. November 2004 A. Freise Non-Linear Alignment Suspended bench External bench Output Mode-Cleaner Non-linear alignment: every kind of computer algorithm performing alignment of the main optics or the main beam The current software from the Napoli group can automatically align the North and West arm cavity using a progressive accuracy (from several 10 urads to less than 1 urad) Automatically align PR to 2 urad (to be improved) The software is now regularly used in the detector operation The next version of the software is planned to also align the input beam and the BS to center the beam on the end mirrors (before the cavity alignment) Provide a new algorithm for the alignment of full VIRGO which is fully automatic and has a better resolution for the PR

04. November 2004 A. Freise Linear Alignment Output Mode-Cleaner VIRGO is the only project to employ the Anderson technique First time this technique is tried for interferometers with suspended mirrors Expected advantages and disadvantages Signals in transmission of the cavity are comparably `clean’ The different degrees of freedom can be detected with comparable strengths in all output ports Possibly a larger coupling of noise into the gravitational wave channel

04. November 2004 A. Freise Frequency Range of Alignment Control DC: beam positions are defined by reference marks, spot position control, below 0.1 Hz around the resonance frequencies of the suspension pendulums the beam follows the input beam from the laser bench, differential wave-front sensing, 0.1 Hz to 5 Hz no active control at the expected signal frequencies

04. November 2004 A. Freise Quadrant Sensors Linear Alignment: Differential wave-front sensing Drift Control: Spot position sensing

04. November 2004 A. Freise Linear Alignment: Current Status Suspended bench External bench Output Mode-Cleaner Interferometer until recently used in recombined mode (Recycling mirror is misaligned) North and West arm cavities are automatically aligned (to the beam) since: North arm: December 2003 West arm: May 2004 Linear alignment ON is the standard condition, no known problems Longest continuous lock >32h

04. November 2004 A. Freise Angular Fluctuations Residual fluctuations: ~ 1 10 Hz ~ <1urad RMS Limited by: input beam jitter resonance peaks of the main suspensions (e.g. 0.6 Hz)

04. November 2004 A. Freise Problems and Solutions (I) Suspended bench External bench Output Mode-Cleaner Large transient when switched from Local Control to Linear Alignment: problem originates in the low frequency components of the control filters could be solved by re-arranging the switches and filters in the DSP Difference between vertical and horizontal readout signals made it impossible to optimize the control matrix: believed to originate in the readout optics (not completely understood) can be solved completely by using independant control matrix for Tx and Ty. This requires one extra phase shifter (one electronic board) per detector. Currently a simple phase shifter (cable) is used. A new set of phase shifters are being made by Frascati, they will be ready in two weeks

04. November 2004 A. Freise Problems and Solutions (II) Suspended bench External bench Output Mode-Cleaner Beam position on terminal benches was moving Supports of terminal benches and of the first big lens after the end mirrors have been changed Beam profile on terminal benches could not be measured because of strong spherical aberration Two big lenses were replaced by doublets

04. November 2004 A. Freise Problems and Solutions (III) Suspended bench External bench Output Mode-Cleaner Several problems and changes with respect to the Global Control (see F. Cavalier’s talk tomorrow) A few minor problems with the Quadrant centering (QaServer), to be fixed by upgrading the software soon Most common problems were related to detector operation only: excited suspensions (300 mHz, 600 mHz) detuned demodulation phases for B7/B8 (1-5 Hz)

04. November 2004 A. Freise Problems and Solutions (…) Suspended bench External bench Output Mode-Cleaner …

04. November 2004 A. Freise From Recombined to Recycled (I) Suspended bench External bench Output Mode-Cleaner We only have one mirror more to control BUT the entire control scheme changes when the PR mirror is aligned: We CAN NOT use the control for the arm cavities any more because for the new alignment readout the `cavities’ as such do not exist any more In the recycling state: either we can control all mirrors or we can control none There are two new readouts to be implemented 2 quadrant diodes in the detection lab and 2 quadrant diodes in the laser lab

04. November 2004 A. Freise Optical Readout Quadrant readout on B2, B5, B7 and B8 The optical readout has been moved from B1 to B5 for the first implementation The telescope setup in the detection lab is different from the design due to lack of space, need to design a new telescope All quadrant diodes are on translation stages: all tested, one broken, can be replaced next week Gains have to be tuned for the full power

04. November 2004 A. Freise Linear Alignment Matrix (I) In total: 8 Gouy phases have to be tuned, 16 demodulation phases to be set. This yields 32 signals to control 10 degrees of freedom (5 horizontal, 5 vertical). Control topology (phases+control matrix) has been designed by G. Giordano. The optical matrix has to be measured to generate two 5x16 control matrices using a  2 reconstruction method. (Without BS control and drift control)

04. November 2004 A. Freise Linear Alignment Matrix (II) Suspended bench External bench Output Mode-Cleaner We want to measure the 32x10 matrix in a few minutes: Requires injecting high frequency lines via the reference mass coils, currently tested by P. Ruggi, requires all coils to be connected to DACs It might be possible to inject such lines continuously (as calibration lines) to measure the optical matrix online, to be discussed Matlab software has been written to automatically extract the matrix amplitude coefficients from frame data, currently extended to the full matrix

04. November 2004 A. Freise From Recombined to Recycled (II) Suspended bench External bench Output Mode-Cleaner As soon as the recycling lock has become more `natural’ we can implement Linear Alignment for full VIRGO The implementation will consist of an very experimental period: During a recycling lock the optical matrix has to be measured The misalignment angles can be reconstructed online using a chi^2 algorithm with this (static) matrix inside the Global Control With these one tries to close Linear Alignment control loops A stable control should be found by understanding the behavior of the control loops during locking tries and by doing an iterative series of matrix measurements and locking tries

04. November 2004 A. Freise Global Control Algorithm Suspended bench External bench Output Mode-Cleaner The current Alignment algorithm inside the Global Control makes use of all the available features: The configuration is performed via database objects Derived channels (triggers, error states, reconstructed angles) are send to the DAQ system On-the-fly switches allow to change between algorithms by clicking a button An extended algorithm has to be written for full VIRGO control: The new channels (error signals, feedback) have to be tested In addition, the chi^2 reconstruction method must be integrated

04. November 2004 A. Freise Beamsplitter Control Suspended bench External bench Output Mode-Cleaner In the final configuration also the local controls of the Beamsplitter should be switched off The Beamsplitter motion is associated to the same degree of freedom as the West input mirror, therefore it cannot be controlled independently Instead a `common’ feedback to BS and WI can be implemented, this requires an additional control loop for the DC position (drift control) In preparation of this work we have already demonstrated Sending WI feedback only to BS Sending `common’ feedback The drift control of the BS

04. November 2004 A. Freise Drift Control beam drifts : injection bench and beam splitter to control 2 axes (DC- 0.1 Hz) DC

04. November 2004 A. Freise Conclusion Output Mode-Cleaner First implementation of the Anderson technique on a large scale interferometer …

04. November 2004 A. Freise End

04. November 2004 A. Freise Example VIRGO Tilt Matrix (16x5)