1. Gingin Advisory Committee Meeting 08 Dec 2009
Introduction:
After the last GAC meeting at the end of July 2009, we started preparing for the high optical power, high finesse cavity on the Gingin east arm for studying parametric instability. We report here the progress and a draft plan for the next 3 months
7/19/2018
GAC Meeting

2. relatively high CO2 heating power is required to enable PI RoC tuning.
East arm extension
Objective:
Radii of curvature of the silica test masses at the margin of the specification
relatively high CO2 heating power is required to enable PI RoC tuning.
arm length extended ~1.4 m
required CO2 laser heating power is reduced from >5W to less than 1W.
7/19/2018
GAC Meeting

3. East arm extension Progress:
Successfully moved tank with the whole vibration isolator inside by 1.4m and inserted one section vacuum pipe.
Special clamps to lock the isolator inside the tank
Special soft lifting springs and supporting structure
Rotated the 80m pipe to fit the flanges of the new vacuum pipe section

4. Change LaCoste stage springs
Objective:
PI Experiment requires excellent vibration isolation.
LaCoste vertical pre-isolation stage (east arm) experienced significant creep (~50gm in 200kg over 6 months), due to spring load near yield stress.
change existing LaCoste springs to new springs with the total spring load < 60% of yield stress + positive coldwork to minimise creep.
7/19/2018
GAC Meeting

5. LaCoste Stage Spring Replacement
Progress:
120 pre-stressed springs for two isolators received.
Pre-cleaned ~60 springs
Final clean and baking of those 60 springs will be done this week before replacing springs for the first isolator before Xmas.
Investigating new Euler-LaCoste pre-isolator: maraging steel Euler springs in LaCoste configuration: zero creep, high internal modes, reduced mass.

6. High power laser
UWA student Lucienne Merrill went to Adelaide for 4 weeks to learn/work on the high power laser assembly.
It was reported that the final configuration will be finished and tested in the coming weeks
To be confirmed by U. Adelaide

7. Upgrade laser room HEPAs
Objective: Reconstruct the HEPA filter system for the laser room to a) keep the laser room cleaner and control the humidity to meet the requirement of the 50W laser; and b) to reduce fan induced noise.
Progress:
We will use 6 of the 8 existing HEPA filters to circulate the laser room clean air. Other 2 filters will be used to keep the positive pressure.
We will separate the HEPA filter’s fan unit from the filter unit, (currently mounted together on laser room roof).
The fans will be suspended from a separate support and connected to the filters by soft ducting.
final design complete, final drawings nearly ready for machining.
7/19/2018
GAC Meeting

8. Laser safety system for 50W laser
Objectives: Improve the laser safety system suitable for the 50W laser
Progress:
One summer student is working to build a laser safety system
Interlock position design
Electronics
Design of the east arm input table enclosure. Prepare for construction
7/19/2018
GAC Meeting

9. Thermal tuning test mass RoC using CO2 laser heating
Objective: to Evaluate the thermal tuning RoC of the test masses.
Progress: Preliminary experiment done on the south arm with sapphire test mass. The experimental setup will be moved to the east arm when fully tested.
Deformation (nm)
X (mm)
Y (mm)
CO2 Laser
Test mass
Vacuum tank
SLD
CCD and Hartmann plate
7/19/2018
GAC Meeting

10. AdLIGO like control system for Gingin
Objectives: To switch the existing Gingin digital control system to AdLIGO like digital control system.
Progress: One complete system (hardware and software built by Bram at ANU) is ready at UWA. One summer student started to learn and to test the individual system at UWA and then move to Gingin south arm for testing in situ. Eventually it will replace all controls at Gingin site.
7/19/2018
GAC Meeting

11. Gingin site seismic noise survey
Objectives:
to provide on-line long term seismic noise data at Gingin site.
combine data with other environment data for long term correlation analysis.
Progress: One summer student started working at Gingin site.
7/19/2018
GAC Meeting

12. Control mass control from upper stage
Objectives:
control mass control is currently referenced to the frame, (potential seismic noise coupling) from this control.
The idea is to test to control the control mass relative to the upper stage to minimise the seismic noise coupling.
Progress: One summer student started working on the modelling of the suspension system.
Control mass
Test mass
7/19/2018
GAC Meeting

13. Tabletop PI experiments
Nd: YAG
High order mode sensing
High order mode generation and frequency offset
Feedback
Acoustic vibration of Silicon Nitride membrane excites high transverse optical mode
3x3 mm2
Objectives: To observe the 3-mode parametric instability and test feedback control scheme.
Progress: difficulty in tuning due to mode interactions mediated by the membrane asymmetry leading to coupled cavity avoided crossing
minimum achievable mode spacing and degraded high order mode finesse: 400kHz achieved, 200kHz desired
Solution: better alignment + higher finesse.
Paper on 2-mode/3-mode interactions: nice physics!
7/19/2018
GAC Meeting

14. Plan for the next 3 months
Complete installation of the new springs for LaCoste stage.
We decided to keep the existing dummy test masses while testing new LaCoste stage.
Control improvements and Isolator Review in February, 2010.
Replace dummy test masses with the new fused silica test masses after the review.
Complete the laser room upgrade and laser safety system for 50 W laser.
Start installation of 50W laser at Gingin as soon as delivered.
Complete testing the CO2 laser thermal tuning and Hartmann sensor monitoring on south arm.
Replace the south arm control with AdLIGO like control system.
Continue fabrication of south arm isolators.
7/19/2018
GAC Meeting