Signal extraction and length sensing for LIGO II RSE

Abstract

Abstract. In anticipation of an upgrade of the LIGO detector to an advanced configuration in 2004, a tabletop prototype of resonant sideband extraction is being designed and constructed at Caltech. We present here two front ally modulated length sensing and control schemes, one in which the signal extraction/recycling mirror is a simple mirror, and one in which it is a Fabry-Perot cavity. Issues regarding the controllability, RF sideband transmission, shot noise, and noise couplings are discussed.Advanced detectors for the LIGO interferometer are planned which use a configuration in which the position of a mirror at the output is used to tune the frequency response, such as resonant sideband extraction (RSE) [1] or dual recycling [2]. RSE can also allow for the storage time of carrier light in the Fabry-Perot arms to be increased, hence the power recycling in the interferometer can be made smaller, reducing thermal lensing in transmissive optics such as the beamsplitter or input test masses without reducing the bandwidth of the detector to gravitational waves.The sensitivity of RSE is well understood [3], but issues of control, lock acquisition and signal extraction are still open, and are the subject of our research. We are considering schemes that, like LIGO I, employ frontal modulation, and which use a set of fixed sidebands on the optical carrier so as to guarantee transmission of all sidebands through an input mode cleaner before entering the interferometer, regardless of the tuning of the output mirror.In LIGO, the signal extraction and control are sensitive to the sideband transmission through the interferometer. The RF sideband transmission to the dark port is well approximated by a three-mirror coupled cavity consisting of the input power recycling mirror, the compound mirror formed by the Michelson interferometer (i.e., the beamsplitter and arm mirrors), and the output signal extraction mirror. In the broadband mode of RSE, where the signal extraction cavity (SEC) is resonant for the optical carrier, both RF sidebands are resonant in this threemirror cavity and are efficiently transmitted to the output. However, in detuned RSE, when the signal extraction cavity is not resonant for the optical carrier, the CP523, Gravitational Waves: Third Edoardo Amaldi Conference, edited by S. Meshkov

A power recycled Michelson interferometer with resonant sideband extraction

“…In addition, if occasional detuning is required, this could be achieved by a macroscopic movement of the signal mirror, in the mode of operation suggested by Mason and Willems. 20 One of the biggest unknowns in this experiment is the ability of single-sideband modulation to be used as an effective signal extraction technique for the gravitational-wave signal. An investigation of techniques to minimize demodulation phase errors would be useful; for example, there may be a way to actively stabilize the demodulation phase to suppress such errors.…”