P010010-00-R - LIGO - California Institute of Technology

Chapter 2
19
Resonant Sideband Extraction
The concept of resonant sideband extraction (RSE) was realized by Jun Mizuno in
1993.[27] It is a Michelson based interferometer with Fabry-Perot cavities in the arms,
and an additional mirror placed at the output of the Michelson. The addition of the
output, or “signal mirror” allows more freedom in choosing the interferometer optics.
This freedom can be used to optimize the distribution of losses in the interferometer,
and thus increase the stored light energy. Another feature is that the frequency
response can be optimized for various gravitational wave signals of interest. The
combination of these features is the focus of this Chapter.
Section 2.1 will discuss the transfer function for gravitational wave signals when
the signal mirror is added at the output of the interferometer. This will be done in
the context of the simpler, idealized configuration of the three mirror coupled cavity.
Section 2.2 will investigate some of the practical limitations to the implementation of
an optical design, mostly due to the effect of losses in the interferometer. Section 2.3
will examine two particular astrophysical sources, and make a first pass at designing
an interferometer whose frequency response is optimized for those sources.
2.1 Frequency Response
The optical layout of an RSE interferometer is shown in Figure 2.1. This is a Michel-
son based interferometer, with Fabry-Perot cavities in the arms. Each Fabry-Perot
cavity is comprised of the input test mass (ITM) at the input, and the end test mass
(ETM) at the end of the cavity. Each cavity is also resonant at the carrier frequency.
The arm cavities are designed to be equal, which is a good approximation in reality,
and an assumption in this chapter. The end mirrors typically are the highest reflectors
available, such that the losses due to transmission through these mirrors is minimized.