Mechanisation of Precision Placement and Catalysis Bonding of Optical Components. Christian Killow ICSO 2016, 21 st October

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1 Mechanisation of Precision Placement and Catalysis Bonding of Optical Components Christian Killow ICSO 2016, 21 st October

2 Overview Gravitational Waves Detecting Gravitational Waves LISA Pathfinder Technology demonstration Precision (sub-micron) assembly of optical systems using hydroxide catalysis bonding

3 Gravitational waves What are they? Ripples in the curvature of spacetime Predicted by Einstein s General Relativity Recent first direct detection by groundbased detectors An incredibly rich source of astronomical information that can not be detected by electromagnetic observations It s like listening to the Universe Credit: ESA C.Carreau

4 Gravitational Wave Observatories The best way we know of to observe gravitational waves is to isolate test masses from local disturbances and monitor their separation as gravitational waves pass through the system Credit: LIGO Credit: ESA We use laser interferometry as the high precision ruler Ground-based detectors, e.g. aligo (Louisiana interferometer shown) with 4 km long arms, operate at frequencies above ~10 Hz The spaceborne interferometric detector for the ESA L3 mission will have gigametre arms and be sensitive in the millihertz region

5 Technology for GW detectors Gravitational waves are incredibly difficult to detect The international effort to detect them took ~four decades We necessarily operate at and sometimes redefine the cutting edge of measurement science We use advanced optical techniques to achieve our goals For a spaceborne detector, it was considered essential to fly a demonstrator mission to reduce risk

6 LISA Pathfinder LISA Pathfinder had, essentially, two tasks: 1. Keep two blocks of metal very still 2. Measure the stillness Credit: ESA Manuel Pedoussaut

7 The LISA Pathfinder optical bench The optical bench monitors the separation of two test masses in gravitational freefall It houses four Mach-Zehnder heterodyne interferometers to monitor test mass motion 10 picometre longitudinal variations 20 nanoradian angular beam motion millihertz frequencies Credit: ESA/ATG medialab

8 Precision, ultra-stable, glue-less bonding Hydroxide catalysis bonding [1-3] was used to attach optical components with sub-micron precision to the LISA Pathfinder optical bench Excellent mechanical properties Had to develop precision alignment The technique now TRL 9 was highly successful in fact it meets the LISA stability requirements! [4] But not scalable not practical to build LISA optical benches in this way 1. Gwo D-H, United States Patent no US 6,284,085 B1 (2001) 2. A. van Veggel and C. Killow, Advanced Optical Technologies, 3(3), pp (2014) 3. M. Armano et al. Phys. Rev. Lett. 116, (2016)

9 Alignment degrees of freedom Control component position x, y and ф define inplane reflection θ/η define out-ofplane reflection In-plane by active alignment Out-of-plane by process control For mechanised bonding, also need to control θ/η and z Control at the microrad and sub-micron level needed Figures from Killow, et al., Appl. Optics 52 (2) pp (2013)

10 Mechanised bonding test assembly

11 Bonded optical system The larger Zerodur baseplate is 6 diameter

12 Absolute alignment results (BS4) X = 9 µm Y = 18 µm The goal was to align Position the measured reflected at beam 220 mm to from overlap reflecting with the optic transmitted beam. Y = 30 µrad These results are reflected beam compared to transmitted beam. X = 32 µrad T = 0 when bonding surfaces brought into contact X is in-plane, Y outof-plane.

13 Result The in-plane reflected beam alignment figures represent component alignment at the 15 µrad level This is a permanent and stable alignment LISA Pathfinder has shown very stable beam positions over >180 days of operation

14 Environmental testing The assemblies were subject to thermal vacuum and shock/vibration testing to similar levels as the LISA Pathfinder optical bench A clamping issue resulted in some failures during vibration testing, but some bonds survived, demonstrating the principle This is a viable way ahead

15 Mechanised bonding summary We have taken a well refined, but difficult to execute, technique and automated the most challenging steps This first step reported here has demonstrated results at a similar level to those seen for LISA Pathfinder Sub-micron and 15 microradian absolute optical component placement Further work will make it possible to manufacture very complex optical assemblies in an industrial environment Thus opening the technology up to new applications Further work is underway to increase the level of mechanisation We have a clear route to developing the technologies to build LISA optical benches

16 Example of a space ruler