Virgo alignment system overview Linear Alignment principle Optical

Virgo alignment system overview ● Linear Alignment principle ● Optical configuration ● Present situation ● Foreseen developments 1 LA electronics meeting, Cascina, 25. 01. 2006

The VIRGO Interferometer Task of the alignment system: Keep 6 mirrors and input beam aligned W N 5 output beams for obtaining error signals EOM 2 LA electronics meeting, Cascina, 25. 01. 2006

Basics of error signal retrieval Phase modulation of input beam Demodulation of photodiode signals at different output beams => longitudinal error signals Quadrant diodes in output beams => Alignment information (differential wavefront sensing) Anderson-Giordano technique 2 quadrant diodes after arm cavities Quadrant diode 3 LA electronics meeting, Cascina, 25. 01. 2006

Detection Can have 1 normal diode and 2 quadrant diodes at each output port 4 LA electronics meeting, Cascina, 25. 01. 2006

Linear alignment setup 5 LA electronics meeting, Cascina, 25. 01. 2006

Present Virgo noise budget Control noise 6 LA electronics meeting, Cascina, 25. 01. 2006

Optimized alignment noise budget Maximized power Optimized mirror centering (0. 2 mm) 7 LA electronics meeting, Cascina, 25. 01. 2006

Present situation Frascati group is leaving Virgo Since 01/2006 Frascati’s responsibilities Original design of alignment system Strategy, optics, prototype experiments, … Design & realization of electronics Problem Continue support for alignment electronics Make new modules / spare modules Continue development for new requirements 8 LA electronics meeting, Cascina, 25. 01. 2006

Developments Present developments More modules needed Installation of 9 th quadrant diode (maybe 10 th) Spares needed New Annecy local oscillator boards, compatible with alignment Phase shifters for standard photodiodes Possible developments Substitute Si diodes with In. Ga. As diodes Better quantum efficiency Lower bias voltage => higher power capability Þ lower noise Reduction of electronics noise Better preamplifier: 5 p. A/rt. Hz -> 1. 6 p. A/rt. Hz (? ) DC signals: pre-amplification / pre-shaping Fast quadrant centering system (Napoli is working on that) LA noise limits sensibility (especially at low frequ. ) 9 LA electronics meeting, Cascina, 25. 01. 2006

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Quadrant photodiode • type EG&G YAG 444 • sensitivity = 0. 45 A/W • DC power = 3 m. Wmax • transimpedance = 2 k • Bias voltage = 180 V 11 LA electronics meeting, Cascina, 25. 01. 2006

QD electronics Quadrant diode box 12 LA electronics meeting, Cascina, 25. 01. 2006

Scheme of LA electronics 13 LA electronics meeting, Cascina, 25. 01. 2006

Noise measurements 14 LA electronics meeting, Cascina, 25. 01. 2006

C 7 matrix Theta. X B 2_q 1_DC B 5_q 1_DC B 2_q 1_ACp B 1 p_q 1_ACp B 7_q 1_ACq B 7_q 2_ACq B 8_q 1_ACp B 8_q 1_ACq Theta. Y B 2_q 1_DC B 5_q 1_DC B 1 p_q 1_ACq B 7_q 1_ACp B 7_q 2_ACq B 8_q 1_ACp B 8_q 2_ACp PR 2. 5 BS -4. 5 NI -6. 4 -24 0. 052 0. 042 -0. 25 9. 41 -0. 108 -0. 035 0. 65 -0. 65 17. 9 0. 0375 0. 052 -0. 052 PR BS NI 0. 33 0. 68 -0. 36 -0. 46 0. 36 -0. 36 -1 1 NE WI 10 1 NE 1 WI 10 WE 15 5. 38 0. 0729 -0. 027 0. 071 -0. 071 WE 1 Theta. X has undergone second diagonalization => mixing of all signals 15 LA electronics meeting, Cascina, 25. 01. 2006

Electronics noise vs. C 7 noise (NE ty) 16 LA electronics meeting, Cascina, 25. 01. 2006

Total LA electronics noise (C 7, calculated) WE ty pure DC error signal => no extra noise vs. AC WI under local control Simulated WI LA curves for comparison C 7 noise not limited by LA electronics noise (but: excess noise) 17 LA electronics meeting, Cascina, 25. 01. 2006

Influence of QD power 18 LA electronics meeting, Cascina, 25. 01. 2006