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

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

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

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

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.

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

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

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

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

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

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

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

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

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