M060056-00.doc - DCC - LIGO Document Control Center Portal

LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY
- LIGO -
CALIFORNIA INSTITUTE OF TECHNOLOGY
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
|Document Type| |20 April 2006|
| |LIGO-M060056-00M | |
|Management | | |
| |
|Advanced LIGO Reference Design |
|David Shoemaker |
|for the Advanced LIGO Team |
| |
| |
| |
|California Institute of Technology |Massachusetts Institute of |
|LIGO Laboratory - MS 18-34 |Technology |
|Pasadena CA 91125 |LIGO Laboratory - NW17-161 |
|Phone (626) 395-2129 |Cambridge, MA 01239 |
|Fax (626) 304-9834 |Phone (617) 253-4824 |
|E-mail: info@ligo.caltech.edu |Fax (617) 253-7014 |
| |E-mail: info@ligo.mit.edu |
www: http://www.ligo.caltech.edu/ Advanced LIGO Reference Design 1. Overview This document describes the technical approach for the first major upgrade
to LIGO, consistent with the original LIGO design and program plan[1]. LIGO consists of conventional facilities and the interferometric detectors.
The LIGO facilities (sites, buildings and building systems, masonry slabs,
beam tubes and vacuum equipment) have been specified, designed and
constructed to accommodate future advanced LIGO detectors. The initial LIGO
detectors were designed with technologies available at the initiation of
the construction project. This was done with the expectation that they
would be replaced with improved systems capable of ultimately performing to
the limits defined by the facilities. In parallel with its support of the initial LIGO construction, the National
Science Foundation (NSF) initiated support of a program of research and
development focused on identifying the technical foundations of future LIGO
detectors. At the same time, the LIGO Laboratory[2] worked with the
interested scientific community to create the LIGO Scientific Collaboration
(LSC) that advocates and executes the scientific program with LIGO[3]. The LSC, which includes the scientific staff of the LIGO Laboratory, has
worked to define the scientific objectives of upgrades to LIGO. It has
developed a reference design and carried out an R&D program plan. This
development has led to this Reference Design for construction of the
Advanced LIGO upgrade following the initial LIGO scientific observing
period. The top-level performance requirements for the complete system are given in
the Advanced LIGO Project Execution Plan (PEP), LIGO-M050303. This document gives a summary of the principal subsystem requirements and
high-level conceptual design of Advanced LIGO. The document is intended to
be dynamic, and will be updated as our technical knowledge improves. 2. Reference Design Configuration and Sensitivity The LIGO Scientific Collaboration, through its Working Groups, has worked
with the LIGO Laboratory to identify a reference design for the Advanced
LIGO detector upgrade. The reference design is planned to lead to a quantum
noise limited interferometer array with considerably increased bandwidth
and sensitivity. The basic optical configuration is a power-recycled and signal-recycled
Michelson interferometer with Fabry-Perot "transducers" in the arms; see
Figure 1. Using the initial LIGO design as a point of departure, Advanced
LIGO requires the addition of a signal-recycling mirror at the output
"dark" port, and changes in the RF modulation and control systems. This
additional mirror allows the gravitational wave induced sidebands to be
stored in the arm cavities or extracted (depending upon the state of
"resonance" of the signal recycling cavity), and allows one to tailor the
interferometer response according to the character of a source (or specific
frequency in the case of a fixed-frequency source). For wideband tuning,
"quantum noise" dominates the instrument noise sensitivity at most
frequencies (see Error! Reference source not found.). Additional details
may be found in Section 12. Interferometer Sensing and Controls Subsystem
(ISC)[4].
Figure 1 Schematic of an Advanced LIGO interferometer, with
representative mirror reflectivities optimized for neutron star
binary inspiral detection. Several new features compared to initial
LIGO are shown: more massive test masses; 20( higher input laser
power; signal recycling; active correction of thermal lensing; an
output mode cleaner. (ETM = end test mass; ITM = input test mass;
PRM = power recycling mirror; SRM = signal recycling mirror; BS =
50/50 beam splitter; PD = photodetector; MOD = phase modulation).
Mode-matching and beam-coupling telescopes not shown. The laser power is increased from 10 W to 180 W, adjustable to be
optimized for the desired interferometer response, given the
quantum limits and limits due to available optical materials. The
resulting circulating power in the arms is roughly 500 kW, to be
compared with the initial LIGO value of ~10 kW. The Nd:YAG pre-
stabilized laser design resembles that of initial LIGO, but with
the addition of a more powerful output stage; see Section 8.
Prestabilized Laser Subsystem (PSL)). The conditioning of the laser
light also follows initial LIGO closely, with a ring-cavity mode
cleaner and reflective mode-matching telescope, although changes to
the modulators and isolators must be made to accommodate the
increase in power; see Section Overview
The Advanced LIGO PSL will be a conceptual extension of the initial LIGO
subsystem, operating at the higher power level necessary to meet the
required Advanced LIGO shot noise limited sensitivity. It will incorporate
a frequency and amplitude stabilized 180 W laser. The Advanced R&D program
related to this subsystem will develop rod optical gain stages that will be
used in an injection-locked power oscillator.
Functional Requirements
The main requirements of the PSL subsystem are output power, and amplitude
and frequency stability. Table 3 lists the reference values of these
requirements. Changes in the readout system allow some requirements to be
less stringent with respect to initial LIGO; the the higher power and
extension to lower frequency provides the principal challenge. Table 3 PSL Requirements |Requirement |Value |
|TEM00 Power |180 W |
|Non-TEM00 Power |