rossMark REVIEW OF SCIENTIFIC INSTRUMENTS 87.014502 (2016) The advanced LIGO input optics Chris L.Mueller,1.a)Muzammil A.Arain,1.b)Giacomo Ciani,1 Ryan.T.DeRosa,2 Anamaria Effler,2 David Feldbaum,1 Valery V.Frolov,3 Paul Fulda,1 Joseph Gleason,1 Matthew Heintze,1 Keita Kawabe,4 Eleanor J.King,5 Keiko Kokeyama,2 William Z.Korth,6 Rodica M.Martin,1 Adam Mullavey,3 Jan Peold,7 Volker Quetschke,8 David H.Reitze,1.c) David B.Tanner,1 Cheryl Vorvick,4 Luke F.Williams,1 and Guido Mueller1 University of Florida,Gainesville.Florida 32611,USA Louisiana State University,Baton Rouge,Louisiana 70803,USA 3LIGO Livingston Observatory,Livingston,Louisiana 70754,USA LIGO Hanford Observatory,Richland,Washington 99352,USA SUniversity of Adelaide,Adelaide.SA 5005,Australia LIGO,California Institute of Technology,Pasadena,California 91125,USA Max-Planck-Institut fuir Gravitationsphysik,30167 Hannover.Germany University of Texas at Brownsville,Brownsville,Texas 78520,USA (Received 27 July 2015:accepted 19 November 2015;published online 22 January 2016) The advanced LIGO gravitational wave detectors are nearing their design sensitivity and should begin taking meaningful astrophysical data in the fall of 2015.These resonant optical interferometers will have unprecedented sensitivity to the strains caused by passing gravitational waves.The input optics play a significant part in allowing these devices to reach such sensitivities.Residing between the pre-stabilized laser and the main interferometer,the input optics subsystem is tasked with preparing the laser beam for interferometry at the sub-attometer level while operating at continuous wave input power levels ranging from 100 mW to 150 W.These extreme operating conditions required every major component to be custom designed.These designs draw heavily on the experience and understanding gained during the operation of Initial LIGO and Enhanced LIGO.In this article,we report on how the components of the input optics were designed to meet their stringent requirements and present measurements showing how well they have lived up to their design.2016 AlP Publishing LLC.[http://dx.doi.org/10.1063/1.4936974] I.INTRODUCTION inject it into the main IFO.The PSL consists of a master laser, an amplifier stage,and a 200 W slave laser which is injection A worldwide effort to directly detect gravitational radi- locked to the amplified master laser.The 200 W output beam ation in the 10Hz to a few kHz frequency range with large is filtered by a short optical ring cavity,the pre-mode cleaner, scale laser interferometers (IFOs)has been underway for the before it is turned over to the IO(see Figure 1).The PSL pre- past two decades.In the United States the Laser Interferometer stabilizes the laser frequency to a fixed spacer reference cavity Gravitational-Wave Observatories (LIGO)in Livingston,LA using a tunable sideband locking technique.The PSL also (LLO)and in Hanford,WA,(LHO)have been operating provides interfaces to further stabilize its frequency and power. since the early 2000's.Initial and Enhanced LIGO (eLIGO) The IFO is a dual-recycled,cavity-enhanced Michelson produced several significant upper limits but did not have the interferometer-as sketched in Figure 2.The field enters the sensitivity to make the first direct detection of gravitational 55 m folded power recycling cavity(PRC)through the power waves.During this time of operation a significant amount recycling mirror(PRM).Two additional mirrors(PR2.PR3) of effort was invested by the LIGO Scientific Collaboration within the PRC form a telescope to increase the beam size to research and design Advanced LIGO (aLIGO),the first from ~2 mm to ~50 mm (Gaussian beam radius)before the major upgrade of Initial LIGO.In 2011 the Initial LIGO large beam is split at the beam splitter and injected into the detectors were decommissioned and installation of these up- two 4 km arm cavities formed by the input and end test masses. grades started.The installation was completed in 2014 and The reflected fields recombine at the BS and send most of the the commissioning phase has begun for many of the upgraded light back to the PRM where it constructively interferes with subsystems at the LIGO observatories.This paper focuses on the injected field.3 This leads to a power enhancement inside the input optics (IO)of aLIGO. the power recycling cavity and provides additional spatial,fre- The main task of the IO subsystem is to take the laser beam quency,and amplitude filtering of the laser beam.The second from the pre-stabilized laser system(PSL)and prepare and output of the BS sends light into the 55 m long folded signal recycling cavity(SRC)which also consists of a beam reduc- ing telescope(SR2,SR3)and the partially reflective signal aElectronic mail:cmueller@phys.ufl.edu b)Present address:KLA-Tencor,Milpitas,California 95035.USA. recycling mirror(SRM). )Present address:LIGO Laboratory.California Institute of Technology, This paper is organized as follows:Section II gives an Pasadena,California 91125.USA. overview of the IO;its functions,components,and the 0034-6748/2016/87(1)/014502/16/$30.00 87,014502-1 2016 AIP Publishing LLC Reuse of AlP Publishing cor subject fo the terms at:https://publishing.aip.org/authors/rights-and-permissions.Download to IP 183195.2516 On:Fri.22Ap1 20160051:35REVIEW OF SCIENTIFIC INSTRUMENTS 87, 014502 (2016) The advanced LIGO input optics Chris L. Mueller, 1,a) Muzammil A. Arain, 1,b) Giacomo Ciani, 1 Ryan. T. DeRosa, 2 Anamaria Effler, 2 David Feldbaum, 1 Valery V. Frolov, 3 Paul Fulda, 1 Joseph Gleason, 1 Matthew Heintze, 1 Keita Kawabe, 4 Eleanor J. King, 5 Keiko Kokeyama, 2 William Z. Korth, 6 Rodica M. Martin, 1 Adam Mullavey, 3 Jan Peold, 7 Volker Quetschke, 8 David H. Reitze, 1,c) David B. Tanner, 1 Cheryl Vorvick, 4 Luke F. Williams, 1 and Guido Mueller1 1University of Florida, Gainesville, Florida 32611, USA 2Louisiana State University, Baton Rouge, Louisiana 70803, USA 3LIGO Livingston Observatory, Livingston, Louisiana 70754, USA 4LIGO Hanford Observatory, Richland, Washington 99352, USA 5University of Adelaide, Adelaide, SA 5005, Australia 6LIGO, California Institute of Technology, Pasadena, California 91125, USA 7Max-Planck-Institut für Gravitationsphysik, 30167 Hannover, Germany 8University of Texas at Brownsville, Brownsville, Texas 78520, USA (Received 27 July 2015; accepted 19 November 2015; published online 22 January 2016) The advanced LIGO gravitational wave detectors are nearing their design sensitivity and should begin taking meaningful astrophysical data in the fall of 2015. These resonant optical interferometers will have unprecedented sensitivity to the strains caused by passing gravitational waves. The input optics play a significant part in allowing these devices to reach such sensitivities. Residing between the pre-stabilized laser and the main interferometer, the input optics subsystem is tasked with preparing the laser beam for interferometry at the sub-attometer level while operating at continuous wave input power levels ranging from 100 mW to 150 W. These extreme operating conditions required every major component to be custom designed. These designs draw heavily on the experience and understanding gained during the operation of Initial LIGO and Enhanced LIGO. In this article, we report on how the components of the input optics were designed to meet their stringent requirements and present measurements showing how well they have lived up to their design. C 2016 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4936974] I. INTRODUCTION A worldwide effort to directly detect gravitational radi￾ation in the 10 Hz to a few kHz frequency range with large scale laser interferometers (IFOs) has been underway for the past two decades. In the United States the Laser Interferometer Gravitational-Wave Observatories (LIGO) in Livingston, LA (LLO) and in Hanford, WA, (LHO) have been operating since the early 2000’s. Initial and Enhanced LIGO (eLIGO) produced several significant upper limits but did not have the sensitivity to make the first direct detection of gravitational waves. During this time of operation a significant amount of effort was invested by the LIGO Scientific Collaboration to research and design Advanced LIGO (aLIGO), the first major upgrade of Initial LIGO. In 2011 the Initial LIGO detectors were decommissioned and installation of these up￾grades started. The installation was completed in 2014 and the commissioning phase has begun for many of the upgraded subsystems at the LIGO observatories. This paper focuses on the input optics (IO) of aLIGO. The main task of the IO subsystem is to take the laser beam from the pre-stabilized laser system1 (PSL) and prepare and a)Electronic mail: cmueller@phys.ufl.edu b)Present address: KLA-Tencor, Milpitas, California 95035, USA. c)Present address: LIGO Laboratory, California Institute of Technology, Pasadena, California 91125, USA. inject it into the main IFO. The PSL consists of a master laser, an amplifier stage, and a 200 W slave laser which is injection locked to the amplified master laser. The 200 W output beam is filtered by a short optical ring cavity, the pre-mode cleaner, before it is turned over to the IO (see Figure 1). The PSL pre￾stabilizes the laser frequency to a fixed spacer reference cavity using a tunable sideband locking technique. The PSL also provides interfaces to further stabilize its frequency and power. The IFO is a dual-recycled, cavity-enhanced Michelson interferometer2 as sketched in Figure 2. The field enters the 55 m folded power recycling cavity (PRC) through the power recycling mirror (PRM). Two additional mirrors (PR2, PR3) within the PRC form a telescope to increase the beam size from ∼2 mm to ∼50 mm (Gaussian beam radius) before the large beam is split at the beam splitter and injected into the two 4 km arm cavities formed by the input and end test masses. The reflected fields recombine at the BS and send most of the light back to the PRM where it constructively interferes with the injected field.3 This leads to a power enhancement inside the power recycling cavity and provides additional spatial, fre￾quency, and amplitude filtering of the laser beam. The second output of the BS sends light into the 55 m long folded signal recycling cavity4 (SRC) which also consists of a beam reduc￾ing telescope (SR2, SR3) and the partially reflective signal recycling mirror (SRM). This paper is organized as follows: Section II gives an overview of the IO; its functions, components, and the 0034-6748/2016/87(1)/014502/16/$30.00 87, 014502-1 © 2016 AIP Publishing LLC Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 183.195.251.6 On: Fri, 22 Apr 2016 00:51:35