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A Backscatter Tolerant Squeezer for Future Generation Gravitational Wave Detectors. Michael Stefszky , Sheon Chua, Conor Mow-Lowry, Sheila Dwyer, Ben Buchler, Ping Koy Lam, Daniel Shaddock, and David McClelland Centre for Gravitational Physics at the Australian National University

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## A Backscatter Tolerant Squeezer for Future Generation Gravitational Wave Detectors

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**A Backscatter Tolerant Squeezer for Future Generation**Gravitational Wave Detectors Michael Stefszky, Sheon Chua, Conor Mow-Lowry, Sheila Dwyer, Ben Buchler, Ping Koy Lam, Daniel Shaddock, and David McClelland Centre for Gravitational Physics at the Australian National University LIGO DCC: G1100728**The Story**• Aim to develop a backscatter tolerant squeezer for future gravitational wave detectors. • Design requirements were met at end of last year • This squeezer is to be tested in the next few months in LIGO Hannford. Michael Stefszky Amaldi9 Cardiff 2011**Squeezing results**Michael Stefszky Amaldi9 Cardiff 2011**Phase jitter and squeezing**• RMS phase noise becomes broadband quantum noise • Similar effect to loss but it is exacerbated by impure squeezing • Jitter at any frequency degrades squeezing at all frequencies Michael Stefszky Amaldi9 Cardiff 2011**Phase jitter and squeezing**• RMS phase noise becomes broadband quantum noise • Similar effect to loss but it is exacerbated by impure squeezing • Jitter at any frequency degrades squeezing at all frequencies Michael Stefszky Amaldi9 Cardiff 2011**Phase jitter and squeezing**• RMS phase noise becomes broadband quantum noise • Similar effect to loss but it is exacerbated by impure squeezing • Jitter at any frequency degrades squeezing at all frequencies Michael Stefszky Amaldi9 Cardiff 2011**Phase jitter and squeezing**• RMS phase noise becomes broadband quantum noise • Similar effect to loss but it is exacerbated by impure squeezing • Jitter at any frequency degrades squeezing at all frequencies Michael Stefszky Amaldi9 Cardiff 2011**Phase jitter and squeezing**• RMS phase noise becomes broadband quantum noise • Similar effect to loss but it is exacerbated by impure squeezing • Jitter at any frequency degrades squeezing at all frequencies Michael Stefszky Amaldi9 Cardiff 2011**The solution: A Box.**Michael Stefszky Amaldi9 Cardiff 2011**The solution: A Box.**Michael Stefszky Amaldi9 Cardiff 2011**The solution: A Box.**Michael Stefszky Amaldi9 Cardiff 2011**Parasitic interferometers**• Scatter which propagates in the original beam path in the (0,0) mode interferometrically couples in phase fluctuations from mirror motion and air currents. Michael Stefszky Amaldi9 Cardiff 2011**Parasitic interferometers**• Scatter which propagates in the original beam path in the (0,0) mode interferometrically couples in phase fluctuations from mirror motion and air currents. Michael Stefszky Amaldi9 Cardiff 2011**Scatter presence test**• By sweeping the phase of a parasitic interferometer with a PZT, the phase noise can be moved out of band. • This technique can be used to diagnose the presence of scattered light. H. Lück et al.,J. Opt. A: Pure Appl. Opt.10 085004 (2008) Michael Stefszky Amaldi9 Cardiff 2011**Scatter presence test**• By sweeping the phase of a parasitic interferometer with a PZT, the phase noise can be moved out of band. • This technique can be used to diagnose the presence of scattered light. H. Lück et al.,J. Opt. A: Pure Appl. Opt.10 085004 (2008) Michael Stefszky Amaldi9 Cardiff 2011**Shot noise with scatter shifting**Following an optical change, scattered light noise was much higher. This was used as an opportunity to test the scatter mitigation technique. Michael Stefszky Amaldi9 Cardiff 2011**The solution: Irises, Dumps and Baffles**Michael Stefszky Amaldi9 Cardiff 2011**The solution: Irises, Dumps and Baffles**Michael Stefszky Amaldi9 Cardiff 2011**Back-reflected light – recent work**• One of the major issues when introducing a squeezer into a gravitational wave detector is the back reflected light from the detection scheme Conor Mow-Lowry GWADW Elba 2011**Back-reflected light**• One of the major issues when introducing a squeezer into a gravitational wave detector is the back reflected light from the detection scheme Conor Mow-Lowry GWADW Elba 2011**Travelling-wave isolation**• The travelling wave OPO provides isolation for back-reflected light from an interferometer. Michael Stefszky Amaldi9 Cardiff 2011**Travelling-wave isolation**• The travelling wave OPO provides isolation for back-reflected light from an interferometer. Michael Stefszky Amaldi9 Cardiff 2011**Travelling-wave isolation**• The travelling wave OPO provides isolation for back-reflected light from an interferometer. Michael Stefszky Amaldi9 Cardiff 2011**Travelling-wave isolation**• The travelling wave OPO provides isolation for back-reflected light from an interferometer. Michael Stefszky Amaldi9 Cardiff 2011**Travelling-wave isolation**• The travelling wave OPO provides isolation for back-reflected light from an interferometer. Michael Stefszky Amaldi9 Cardiff 2011**Travelling-wave isolation**• The travelling wave OPO provides isolation for back-reflected light from an interferometer. Michael Stefszky Amaldi9 Cardiff 2011**Travelling-wave isolation**• The travelling wave OPO provides isolation for back-reflected light from an interferometer. Michael Stefszky Amaldi9 Cardiff 2011**Travelling-wave isolation**• The travelling wave OPO provides isolation for back-reflected light from an interferometer. Michael Stefszky Amaldi9 Cardiff 2011**Travelling-wave isolation**Interfering the very low power back-reflected beam with the homodyne local oscillator. The resulting retro-reflectivity is 2.3e-5, or 46 dB of isolation. Michael Stefszky Amaldi9 Cardiff 2011**Conclusions**• We have seen squeezing with a travelling wave OPO which is: • Spectrally flat • Stable over 90 minutes • Large in magnitude and quite pure • RMS phase noise and scatter were our main enemies • There are improvements to be made to the detection chain which should result in 9+ dB of squeezing with the current OPO. • Squeezer soon to be tested in LIGO Hannford! Michael Stefszky Amaldi9 Cardiff 2011**Squeezing at 500 Hz**Michael Stefszky Amaldi9 Cardiff 2011**Bow-Tie Parameters**• Cavity Length: 28cm • Finesse: 40 @ 1064nm, 17 @ 532nm • FSR: 1GHz • Threshold: Approx. 90mW • Escape Efficiency: Approx. 95% • Waist: 34um @ 1064nm • Input Coupler R: 70%@532nm, 87.5%@1064nm

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