Interface Control Document for the ISC sub-system
Preface
This is a draft of the ICD for the LCGT-ISC sub-system.
Sub-System Definition
The role of the Interferometer Sensing and Control (ISC) sub-system is to keep the interferometer at its optimal operation point and extract the gravitational wave signal with low noise. This sub-system can be functionally broken into two parts: Sensing and Control.
Sensing
In order to control the interferometer, we have to know the state of the interferometer. Sensing part of this sub-system defines the methods to extract information about the state of the interferometer. We sort the degrees of freedom of an interferometer into three categories.
Length Sensing
There are 5 length DOFs to be controlled for a Dual-Recycled Fabry-Perot Michelson Interferometer (DRFPMI).
Name |
Notation |
Description |
Michelson (MICH) |
l- |
Differential change of the Michelson arm lengths |
Power Recycling Cavity Length (PRCL) |
l+ |
Length of the power recycling cavity |
Signal Recycling Cavity Length (SRCL) |
ls |
Length of the signal recycling cavity |
Differential Arm Length (DARM) |
L- |
Differential change of the arm cavity lengths |
Common Arm Length (CARM) |
L+ |
Common change of the arm cavity lengths |
Alignment Sensing
Control