1. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY Violin-Mode Detector N.A. Lockerbie and K.V. Tokmakov Hannover 27 January, 2010

2. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY Shadow sensor. One required per fibre. Infrared LED source. One split-photodiode detector, per fibre—differential output. Need compensation for drift in each fibre’s position (  0.5 mm). –use multiple LED sources (no moving parts) –use sub-miniature LEDs + ‘Galilean’ optical arrangement. Overview of VM detection system for Advanced LIGO = 890 nm. Gold-coated mirrors. 5 x columns of 16 IR LEDs. Increments of 0.6  in shadow offset angle.

3. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY Violin-mode (VM) detection: Mechanical / Optical: 1

4. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY Mockup of a bar (column) of infrared LEDs in aluminium alloy MACOR found to be unsuitable. Aluminium Nitride found to be unsuitable. PEEK has been used.

5. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY Dual split-PD-detector housing

6. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY 4 x IR LED sources 2 x dual PD detectors Violin-mode (VM) detection: Mechanical / Optical: parts

7. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY Violin-mode (VM) detection: Electronics 19” rack- mounted units Plan view

8. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY VM detection electronics—for 19" rack mounting

9. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY AC amplification Could now make R F >> R i i is the ‘Violin-Mode’ signal.

10. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY Violin-mode differential Amplifier (x4)

11. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY Frequency Response of Violin-Mode Amplifier: theory = 100= 10 Therefore expect mid-band AC/DC gain ratio = 1000. Two zeroes (at s = 0, i.e., no DC response):  40 dB/decade roll-off towards DC. Transfer Function of V-M Amplifier (ratio of AC / DC gain): - Three (Four) poles:  20 dB (  40 dB)/decade roll-off towards high frequencies, (since a 1- or 2- pole excess over the number of zeroes).  3 dB frequencies: 240 Hz and 12.16 kHz. Theoretical frequency response of VM amplifier

12. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY Performance of prototype Violin-mode differential Amplifier (680 pF)

13. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY A dual-rail version of the “noise finessing” circuit was also constructed. It had a significant impact on the broadband VM Amplifier’s AC output noise. Such ‘Noise Finessing’ circuits now have been added to all internal regulated supplies within the VM detection system’s 19” rack:  15 V,  15 V (IR LED source supply),  12 V, and  5 V. Ref.: “Finesse voltage regulator noise !” http://www.wenzel.com/documents/finesse.html ‘Noise Finessing:’ Voltage Regulator Noise Reduction: 1

14. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY ‘Noise Finessing:’ Voltage Regulator Noise Reduction: 2 (at output of  100 AC Amplifier ). at AC output. 50 Hz

15. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY Expect sensitivity of approx. 5 x 10  11 m/  Hz. Expected displacement sensitivity of VM detection system

16. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY Electrostatic Driver (T080038-00-K )

17. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY ES Driver: Performance 800 V p-p output, DC-20 kHz Power Spectral Density 26.4 nV/  Hz, referred to input (newer non water-cooled version is 17.4 nV/  Hz, 2 kHz BW).

18. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY Future areas of interest Interferometric sensing of test- mass modes. QND displacement sensing. Low-noise electronics. Control theory and application. Digital filtering. Local microcontroller-based control (programmed in C).