Advanced LIGO LIGO-T000092-02-D
LIGO Laboratory / LIGO Scientific Collaboration
LIGO-T0000xx-02-D ADVANCED LIGO 10/4/00
Auxiliary Optics Support System
Design Requirements Document, Volume 2:
Photon Calibrator
Michael Smith, Phil Willems
Distribution of this document:
LIGO Science Collaboration
This is an internal working note
of the LIGO Project.
California Institute of TechnologyLIGO Project – MS 18-34
1200 E. California Blvd.
Pasadena, CA 91125
Phone (626) 395-2129
Fax (626) 304-9834
E-mail: / Massachusetts Institute of Technology
LIGO Project – NW17-161
175 Albany St
Cambridge, MA 02139
Phone (617) 253-4824
Fax (617) 253-7014
E-mail:
LIGO Hanford Observatory
P.O. Box 1970
Mail Stop S9-02
Richland, WA 99352
Phone 509-372-8106
Fax 509-372-8137 / LIGO Livingston Observatory
P.O. Box 940
Livingston, LA 70754
Phone 225-686-3100
Fax 225-686-7189
http://www.ligo.caltech.edu/
Table of Contents
1 Introduction 7
1.1 Purpose 7
1.2 Scope 7
1.2.1 Photon Calibrator 7
1.2.2 Photon Calibrator Controls. 7
1.3 Definitions 7
1.4 Acronyms 8
1.5 Applicable Documents 9
1.5.1 LIGO Documents 9
1.5.2 Non-LIGO Documents 9
2 General description 10
2.1 Specification Tree 10
2.2 Photon Calibrator and Photon Calibrator Controls Perspective 11
2.3 Photon Calibrator and Photon Calibrator Controls Functions 12
2.4 Photon Calibrator and Photon Calibrator Controls Constraints 12
2.5 Assumptions and Dependencies 12
2.5.1 Core Optics Parameters 12
2.5.2 Interferometer Design Parameters 13
2.5.3 ISC Interface Characteristics 13
2.5.4 Seismic Environment 14
3 Requirements 15
3.1 Photon Calibrator and Photon Calibrator Controls Requirements 15
3.1.1 Introduction 15
3.1.2 Photon Calibrator and Photon Calibrator Controls Characteristics 15
3.1.2.1 Photon Calibrator and Photon Calibrator Controls Performance Characteristics 15
3.1.2.2 Photon Calibrator Physical Characteristics 16
3.1.2.3 Photon Calibrator Interface Definitions 16
3.1.2.4 Photon Calibrator Reliability 17
3.1.2.5 Photon Calibrator Maintainability 17
3.1.2.6 Photon Calibrator Environmental Conditions 17
3.1.2.7 Photon Calibrator Transportability 18
3.1.3 Photon Calibrator Design and Construction 19
3.1.3.1 Materials and Processes 19
3.1.3.2 Photon Calibrator Workmanship 20
3.1.3.3 Photon Calibrator Interchangeability 20
3.1.3.4 Photon Calibrator Safety 20
3.1.3.5 Photon Calibrator Human Engineering 20
3.1.4 Photon Calibrator Assembly and Maintenance 21
3.1.5 Photon Calibrator Documentation 21
3.1.5.1 Photon Calibrator Specifications 21
3.1.5.2 Photon Calibrator Design Documents 21
3.1.5.3 Photon Calibrator Engineering Drawings and Associated Lists 21
3.1.5.4 Photon Calibrator Technical Manuals and Procedures 21
3.1.5.5 Photon Calibrator Documentation Numbering 22
3.1.5.6 Photon Calibrator Test Plans and Procedures 22
3.1.6 Photon Calibrator Logistics 22
3.1.7 Photon Calibrator Precedence 22
3.1.8 Photon Calibrator Qualification 22
4 Quality Assurance Provisions 23
4.1 General 23
4.1.1 Responsibility for Tests 23
4.1.2 Special Tests 23
4.1.2.1 Engineering Tests 23
4.1.2.2 Reliability Testing 23
4.1.3 Configuration Management 23
4.2 Quality conformance inspections 23
4.2.1 Inspections 23
4.2.2 Analysis 24
4.2.3 Demonstration 24
4.2.4 Similarity 24
4.2.5 Test 24
5 Preparation for Delivery 25
5.1 Preparation 25
5.2 Packaging 25
5.3 Marking 25
6 Notes 26
Appendices
Appendix A Quality Conformance Inspections 99
Table of Tables
Table 1 Environmental Performance Characteristics 16
Table 2 Quality Conformance Inspections 26
Table of Figures
Figure 1: Overall LIGO detector requirement specification tree 10
1 Introduction
1.1 Purpose
The purpose of this document is to describe the design requirements for the Auxiliary Optics Subsystems (AOS) Photon Calibrator. Primary requirements are derived (“flowed-down”) from the LIGO principal science requirements. Secondary requirements, which govern Detector performance through interactions between AOS and other Detector subsystems, have been allocated by Detector Systems Engineering.
1.2 Photon Calibrator Scope
The Photon Calibrator subsystem will provide a light beam that actuates the End Test Masses (ETMs) of the interferometer by means of radiation pressure. It will take its control signals from the Length Sensing and Control system. All software and electronics necessary to control the Photon Calibrator subsystem to faithfully respond to the control signals provided by the Length Sensing and Control system are part of the scope. This subsystem forms part of the interface between ISC and SUS. The Photon Calibrator does not send or receive any control signals from the SUS subsystem. No optic in LIGO other than the ETMs will have Photon Calibrators.
1.3 Definitions
1.4 Acronyms
LIGO - Laser Interferometer Gravity Wave Observatory
IOO - Input Optics
DRD - Design Requirements Document
SRD - Science Requirements Document
ETM - End Test Mass in the interferometer
AR - Antireflection Coating
HR - Reflective mirror coating
SEI - Seismic Isolation subsystem
SUS - Suspension subsystem
ISC- Interferometer Sensing and Control
LSC - Length Sensing and Control
COC - Core Optics Components
ASC - Alignment Sensing and Control
IFO - LIGO interferometer
HAM - Horizontal Access Module
BSC - Beam Splitter Chamber
TBD - To Be Determined
APS - anti-symmetric port signal
SPS - symmetric port signal
rms - root-mean-square
1.5 Applicable Documents
1.5.1 LIGO Documents
Core Optics Support Design Requirements Document lIGO-T970071-03-D
Core Optics Components DRD: LIGO-Exxx
ISC Reference Design
Seismic Isolation DRD, LIGO-T960065-02-D
Locally Damped Test Mass Motion, LIGO-T970092-00-D
Advanced LIGO Detector Design Requirements Document: LIGO-Exxx
Core Optics Support Conceptual Design, LIGO-T970072-00-D
COS Beam Dump and Stray Light Baffle Revised Req. and Concepts LIGO-T980103-00-D
Up-conversion of Scattered Light Phase Noise from Large Amplitude Motions, LIGO-T980101-00D
Effect of PO Telescope Aberrations on Wavefront Sensor Performance, LIGO-T980007-00-D
LIGO Vacuum Compatibility, Cleaning Methods and Procedures, LIGO-E960022-00-D
ASC Optical Lever Design Requirement Document, LIGO-T950106-01-D
LIGO-E000007-00
LIGO Naming Convention (LIGO-E950111-A-E)
LIGO Project System Safety Management Plan LIGO-M950046-F
LIGO EMI Control Plan and Procedures (LIGO-E960036)
Derivation of CDS Rack Acoustic Noise Specifications, LIGO-T960083
Specification Guidance for Seismic Component Cleaning, Baking, and Shipping Preparation (LIGO-L970061-00-D)
COS Preliminary Design T980010-01-D
1.5.2 Non-LIGO Documents
2 General description
2.1 Photon Calibrator Perspective
Radiation pressure provides a potentially very well-characterized force on a mirror that can be used to calibrate the interferometer response to gravitational waves. This calibration is complementary to other techniques, such as calibration through error signal analysis of optics swinging through fringes. The Photon Calibrator provides this force and the means to sufficiently characterize it.
2.2 Photon Calibrator and Photon Calibrator Controls Functions
The Photon Calibrator shall reflect off a surface of the ETM a laser beam whose power is controlled by signals provided by the ISC subsystem. This power will itself be measured and stored for data analysis.
The main purpose of the Photon Calibrator is to provide actuation for on the ETM as dictated by ISC for calibration purposes.
2.3 Photon Calibrator and Photon Calibrator Controls Constraints
LIGO must operate continuously; therefore this subsystem must be designed with high reliability and low mean time to repair. As this subsystem introduces light into the interferometer vacuum chamber, it must not introduce significant stray light at the interferometer sensing ports, especially the ASP.
2.4 Assumptions and Dependencies
2.4.1 Core Optics Parameters
The following ETM parameters were taken from the Core Optics Components Design Requirements Document: LIGO-T000127-01-D.
Physical Quantity / ETMAR coating @ 1060 nm / <0.0003
mirror reflectivity @ 1060 nm / 0.99994
refractive index @ 1064 nm / 1.44963
1ppm power contour radius, mm / 168
beam radius parameter w, mm / 60
Mirror diameter, mm / 340
Mirror thickness, mm / 200
2.4.2 Interferometer Design Parameters
The Photon Calibrator can potentially inject stray light into the interferometer. The stray light calculations were based on the following assumed parameters:
Laser input power / 125 wattsSPS power / 2.5 watts
APS power / 1.0 Watt
IFO Gaussian beam radius, w / 60 mm
Recycling cavity gain / 16.8
Arm cavity gain / 789
2.4.3 Displacement Noise Parameters
The force noise requirements in this document are referenced to the longitudinal displacement noise requirement for the test masses. The requirement is the upper limit of 5x10-20 m/ÖHz at 10 Hz, falling as 1/f, and 10-19 m/ÖHz at 10 Hz, falling as (1/f)2.
2.4.4 ISC Interface Characteristics
The ISC interface to the Photon Calibrator will be through 16384 kHz, 16 bit ADCs and DACs.
2.4.5 Seismic Environment
The photon pressure noise calculations in this document are based on the assumption that the Photon Calibrator laser beam jitters with the noise spectrum and amplitude of the flange to which it is mounted. The ground noise spectrum is assumed to be the LIGO Composite Ground Noise Spectrum for frequencies between 10 and 1000 Hz, as described in figure 10, LIGO-T960065.
3 Requirements
3.1 Photon Calibrator Requirements
3.1.1 Photon Calibrator Characteristics
3.1.1.1 Photon Calibrator Performance Characteristics
The Photon Calibrator shall provide a sinusoidal force on the ETM of up to 0.1 nN amplitude with a frequency controllable over the range 10-2048 Hz.
In order that the Photon Calibrator induce less than 1/10th the displacement noise required for the ETM if it is used during data collection, the noise force shall be less than the upper limit of
7.9x10-16 N/ÖHz at 10 Hz, rising as 1/f, and 1.6x10-15 N/ÖHz, independent of frequency.
The Photon Calibrator force centering on the ETM shall be sufficient that operation of the Photon Calibrator over its full power range does not tilt the ETM beyond the technical pitch and yaw noise requirements specified in the SUS DRD. In addition the Photon Calibrator beam jitter shall be sufficiently small that at full power it does not tilt the ETM beyond the technical pitch and yaw noise requirements specified in the SUS DRD. In addition, the Photon Calibrator centering shall be sufficient to satisfy the displacement certainty mentioned later in this subsection.
Occasional large glitches in the power output of the Photon Calibrator can be interpreted as gravitational wave bursts. If large enough, they could potentially throw the interferometer out of lock. Glitches in the Photon Calibrator power output large enough to induce detectable glitches in the ASP at design sensitivity shall be detected within the Photon Calibrator subsystem. The rate of such ‘ASP-detectable’ glitches shall be less than one per day. The size of a lock-ending glitch is not known as of the writing of this document.
The displacement of the HR surface of the ETM caused by the Photon Calibrator shall be absolutely known to within 1%.
3.1.1.2 Photon Calibrator Physical Characteristics
The Photon Calibrator has no special physical characteristics it need satisfy.
3.1.1.3 Photon Calibrator Interface Definitions
3.1.1.3.1 Interfaces to other LIGO detector subsystems
3.1.1.3.1.1 Mechanical Interfaces
Any steering and/or folding mirrors inside the vacuum shall bolt to the SEI BSC platform. Lasers and optics external to the vacuum system shall reside on optical benches supported by the viewport flanges and viewport adapter.
3.1.1.3.1.2 Electrical Interfaces
The Photon Calibrator shall receive a digital control signal from ISC proportional to the force required (equivalently, the output light power). The Photon Calibrator shall deliver to ISC a signal calibrated to within 1% of the optical power delivered to the ETM.
3.1.1.3.1.3 Optical Interfaces
The Photon Calibrator beams will pass through viewports provided in the spools nearest the ETM BSC chambers and reflect off of one or more spots on the HR surfaces of the ETMs. The reflected beams will be dumped within the vacuum chamber or beam tubes.
3.1.1.3.1.4 Stay Clear Zones
Any steering or folding mirrors inside the vacuum tank must stay clear of the 1ppm radius of the main arm cavity beam. They must also not interfere with other auxiliary optic beams or apertures, such as sampled ETM transmission beams, cameras, or optical lever beams.
3.1.1.3.2 Interfaces external to LIGO detector subsystems
3.1.1.3.2.1 Mechanical Interfaces
Lasers and optics external to the vacuum system will reside on optical benches or in beam enclosures.
3.1.1.3.2.2 Electrical Interfaces
3.1.1.3.2.3 Stay Clear Zones
3.1.1.4 Photon Calibrator Reliability
The laser used in the Photon Calibrator could operate continuously for months. It is also expected to be a relatively conservative technology. It therefore must operate with a Mean Time Between Failures (MTBF) of one year for out of vacuum components and three years for in-vacuum components, which require a vacuum vent to service.
Recalibration of the Photon Calibrator shall require no more than one day to perform.
3.1.1.5 Photon Calibrator Maintainability
The laser and optics external to the vacuum system will require no more than one day to replace or repair.
3.1.1.6 Photon Calibrator Environmental Conditions
3.1.1.6.1 Natural Environment
3.1.1.6.1.1 Temperature and Humidity
Table 1 lists the temperature and humidity environmental requirements on the Photon Calibrator.
Table 1 Environmental Performance Characteristics
Operating / Non-operating (storage) / Transport+0 C to +50 C, 0–90 % RH / 40 C to +70 C, 0–90 % RH / 40 C to +70 C, 0–90 % RH
3.1.1.6.1.2 Atmospheric Pressure
The Photon Calibrator is expected to contain standard laser and optomechanical equipment. No special requirements against atmospheric pressure are anticipated.
3.1.1.6.1.3 Seismic Disturbance
The Photon Calibrator is expected to contain standard laser and optomechanical equipment. No special requirements against seismic disturbance are anticipated.
3.1.1.6.2 Induced Environment
3.1.1.6.2.1 Electromagnetic Radiation
Electrical equipment associated with the subsystem shall meet the EMI and EMC requirements of VDE 0871 Class A or equivalent. The subsystem shall also comply with the LIGO EMI Control Plan and Procedures (LIGO-E960036).
3.1.1.6.2.2 Acoustic
Equipment shall be designed to produce the lowest levels of acoustic noise as possible and practical. As a minimum, equipment shall not produce acoustic noise levels greater than specified in Derivation of CDS Rack Acoustic Noise Specifications, LIGO-T960083.
3.1.1.6.2.3 Optical
The Photon Calibrator and Photon Calibrator Controls subsystem shall not produce a laser safety hazard during normal operation.
3.1.1.6.2.4 Mechanical Vibration
Mechanical vibration from the subsystem shall not increase the vibration amplitude of the facility floor within 1 m of any other vacuum chambers and equipment tables by more than 1 dB at any frequency between 0.1 Hz and 10 kHz. Limited narrowband exemptions may be permitted subject to LIGO review and approval.
3.1.1.7 Photon Calibrator Transportability
All items shall be transportable by commercial carrier without degradation in performance. As necessary, provisions shall be made for measuring and controlling environmental conditions (temperature and accelerations) during transport and handling. Special shipping containers, shipping and handling mechanical restraints, and shock isolation shall be utilized to prevent damage. All containers shall be movable for forklift. All items over 100 lbs. which must be moved into place within LIGO buildings shall have appropriate lifting eyes and mechanical strength to be lifted by cranes.