Optimal alignment sensing of a readout mode cleaner cavity

N. Smith-Lefebvre, S. Ballmer, M. Evans, S. Waldman, K. Kawabe, V. Frolov, N. Mavalvala

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


Critically coupled resonant optical cavities are often used as mode cleaners in optical systems to improve the signalto-noise ratio (SNR) of a signal that is encoded as an amplitude modulation of a laser beam. Achieving the best SNR requires maintaining the alignment of the mode cleaner relative to the laser beam on which the signal is encoded. An automatic alignment system that is primarily sensitive to the carrier field component of the beam will not, in general, provide optimal SNR. We present an approach that modifies traditional dither alignment sensing by applying a large amplitude modulation on the signal field, thereby producing error signals that are sensitive to the signal sideband field alignment. When used in conjunction with alignment actuators, this approach can improve the detected SNR; we demonstrate a factor of 3 improvement in the SNR of a kilometer-scale detector of the Laser Interferometer Gravitational-Wave Observatory. This approach can be generalized to other types of alignment sensors.

Original languageEnglish (US)
Pages (from-to)4365-4367
Number of pages3
JournalOptics Letters
Issue number22
StatePublished - Nov 15 2011

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics


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