An Automated Photodetector Frequency Response Measurement System for LIGO

ORAL

Abstract

LIGO will detect gravitational waves using laser interferometers that will be quantum noise limited over most of the apparatus's operating frequency range. To build an interferometric gravitational wave detector that works at the limits set by quantum mechanics, one must ensure that the detector can be controlled and read out optically. In the LIGO interferometers, several photodiodes are used to sense various degrees of freedom and provide feedback signals so that the cavities are in optical resonance. It is thus necessary to treat the photodiode and its readout electronics as systems whose performances, including frequency response, can change over time and with changing operating conditions. This project's purpose was to build an automatic frequency response measurement system for the interferometer's photodiodes. We use a modulated diode laser coupled through a fiber optic distribution system to illuminate the photodiodes, and then automatically and quickly measure the frequency response of each photoreceiver using a network analyzer and an RF switch to select the photodiodes one after another. The experiment was carried out at Caltech on the LIGO 40m prototype interferometer and designed with Advanced LIGO scalability in mind.

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Authors

  • Alexander Cole

    Pomona Coll

  • Sergey Savrasov

    Hartnell College, Cal State Univ- Long Beach, University of California, Davis, School of Natural Science, University of California, Merced, Seagate Technology, Materials Science and Engineering, National Tsing Hua University, Taiwan, University of California - Berkeley, University of Colorado, Boulder -- Dept of Physics, University of California, Berkeley -- Dept of Chemistry, UC Merced, California State University, Fresno, California Institute of Technology, California State University, Long Beach, La Canada Flintridge, CA, Department of Physics, Florida A\&M University, Tallahassee, FL-32307, Physical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, CA-94550, Cal State Univ East Bay, American River College, UC Santa Cruz, Notre Dame High School, Benedict College, Lawrence Livermore National Laboratory, Tuskegee University, California State University, Dominguez Hills, Sonoma State University, Carnegie Observatories, University of California, Los Angeles, Institute of Astronomy, University of Cambridge, UK, University of California, Santa Barbara, University of Alabama, MPIfR, Bonn, Germany, Stanford University, University of California - Davis