Title

Optical Follower feedback control loop for the photon calibrator at LIGO

Presenter Information

Rolf Minton

Document Type

Oral Presentation

Location

SURC Ballroom A

Start Date

17-5-2012

End Date

17-5-2012

Abstract

The Advanced Laser Interferometer Gravitational wave Observatory (LIGO) calibration will rely on power-modulated auxiliary laser beams to induce time-varying displacements of the end test masses (ETMs). Photon calibration (Pcal) induces two kinds of displacement noise, relative power noise (RPN) and harmonic noise due to impurities in the modulated signal. To minimize the injection of displacement noise, the sinusoidal power modulation needs to be purified. To improve the spectral purity, we employ an "Optical Follower" feedback control system. The Optical Follower samples a fraction of the modulated power and compares it with a reference waveform. The difference is fed back to an acousto-optic modulator (AOM) to reduce differences between the generated and the reference waveforms. The servo was able to meet the requirements for harmonic noise and extended the linear range of the AOM. However more work needs to be done to improve RPN. This project was a proof of principle to design and fabricate an Optical Follower servo during a summer Research Experience for Undergraduate (REU) at LIGO in 2011.

Poster Number

2

Faculty Mentor(s)

Michael Braunstein, Rick Savage, Paul Schwinberg, Jonathan Berliner

Additional Mentoring Department

Physics

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May 17th, 11:15 AM May 17th, 1:44 PM

Optical Follower feedback control loop for the photon calibrator at LIGO

SURC Ballroom A

The Advanced Laser Interferometer Gravitational wave Observatory (LIGO) calibration will rely on power-modulated auxiliary laser beams to induce time-varying displacements of the end test masses (ETMs). Photon calibration (Pcal) induces two kinds of displacement noise, relative power noise (RPN) and harmonic noise due to impurities in the modulated signal. To minimize the injection of displacement noise, the sinusoidal power modulation needs to be purified. To improve the spectral purity, we employ an "Optical Follower" feedback control system. The Optical Follower samples a fraction of the modulated power and compares it with a reference waveform. The difference is fed back to an acousto-optic modulator (AOM) to reduce differences between the generated and the reference waveforms. The servo was able to meet the requirements for harmonic noise and extended the linear range of the AOM. However more work needs to be done to improve RPN. This project was a proof of principle to design and fabricate an Optical Follower servo during a summer Research Experience for Undergraduate (REU) at LIGO in 2011.