REVIEW OF SCIENTIFIC INSTRUMENTS 83.033109(2012) Thermal effects in the Input Optics of the Enhanced Laser Interferometer Gravitational-Wave Observatory interferometers Katherine L.Dooley,1.a)Muzammil A.Arain,1.b)David Feldbaum,1 Valery V.Frolov,2 Matthew Heintze,1 Daniel Hoak,2.c)Efim A.Khazanov,3 Antonio Lucianetti,1.d) Rodica M.Martin,1 Guido Mueller,1 Oleg Palashov,3 Volker Quetschke,1.) David H.Reitze,1.R.L.Savage,4 D.B.Tanner,1 Luke F.Williams,1 and Wan Wu1.9) University of Florida,Gainesville,Florida 32611.USA 2LIGO,Livingston Observatory,Livingston,Louisiana 70754.USA 3Institute of Applied Physics,Nizhny Novgorod 603950.Russia ALIGO.Hanford Observatory,Richland,Washington 99352.USA (Received 9 December 2011;accepted 23 January 2012;published online 23 March 2012) We present the design and performance of the LIGO Input Optics subsystem as implemented for the sixth science run of the LIGO interferometers.The Initial LIGO Input Optics experienced thermal side effects when operating with 7 W input power.We designed,built,and implemented improved versions of the Input Optics for Enhanced LIGO,an incremental upgrade to the Initial LIGO inter- ferometers,designed to run with 30 W input power.At four times the power of Initial LIGO,the Enhanced LIGO Input Optics demonstrated improved performance including better optical isolation, less thermal drift,minimal thermal lensing,and higher optical efficiency.The success of the Input Optics design fosters confidence for its ability to perform well in Advanced LIGO.2012 American Institute of Physics.[http://dx.doi.org/10.1063/1.3695405] I.INTRODUCTION the arm lengths,producing signal at the AS port proportional The field of ground-based gravitational-wave (GW) to the GW strain and the input power.The Fabry-Perot cavi- physics is rapidly approaching a state with a high likelihood ties in the Michelson arms and a power recycling mirror(RM) of detecting GWs for the first time in the latter half of this at the symmetric port are two modifications to the Michelson interferometer that increase the laser power in the arms and decade.Such a detection will not only validate part of Ein- stein's general theory of relativity,but also initiate an era therefore improve the detector's sensitivity to GWs. of astrophysical observation of the universe through GWs. A network of first generation kilometer scale laser in- Gravitational waves are dynamical strains in space-time,h terferometer gravitational-wave detectors completed an in- =AL/L,that travel at the speed of light and are gener- tegrated 2-year data collection run in 2007,called Science Run 5(S5).The instruments were:the American Laser Inter- ated by non-axisymmetric acceleration of mass.A first de- ferometer Gravitational-Wave Observatory (LIGO).one in tection is expected to witness an event such as a binary black hole/neutron star merger. Livingston,LA with 4 km long arms and two in Hanford, WA with 4 km and 2 km long arms;the 3 km French-Italian The typical detector configuration used by current gen- eration gravitational-wave observatories is a power-recycled detector VIRGO (Ref.3)in Cascina,Italy;and the 600 m Fabry-Perot Michelson laser interferometer featuring sus- German-British detector GEO(Ref.4)located near Hannover, pended test masses in vacuum as depicted in Figure 1.A Germany.Multiple separated detectors increase detection confidence through signal coincidence and improve source lo- diode-pumped,power amplified,and intensity and frequency stabilized Nd:YAG laser emits light at =1064 nm.The calization via waveform reconstruction. The first generation of LIGO,now known as Initial laser is directed to a Michelson interferometer whose two arm LIGO,achieved its design goal of sensitivity to GWs in the lengths are set to maintain destructive interference of the re- combined light at the anti-symmetric(AS)port.An appropri- 40-7000 Hz band,including a record strain sensitivity of ately polarized gravitational wave will differentially change 2 x 10-23/Hz at 155 Hz.However,only nearby sources produce enough GW strain to appear above the noise level of Initial LIGO and no gravitational wave has yet been found aAuthor to whom correspondence should be addressed.Electronic mail: in the S5 data.A second generation of LIGO detectors,Ad- kate.dooley@aei.mpg.de.Present address:Albert-Einstein-Institut,Max- Planck-Institut fur Gravitationsphysik,D-30167 Hannover,Germany. vanced LIGO,has been designed to be at least an order of b)Present address:KLA-Tencor,Milpitas.California95035,USA. magnitude more sensitive at several hundred Hz and above c)Present address:University of Massachusetts-Amherst,Amherst, Massachusetts 01003.USA. and to give an impressive increase in bandwidth down to d)Present address:Ecole Polytechnique,91128 Palaiseau Cedex,France. 10 Hz.Advanced LIGO is expected to open the field of GW e)Present address:The University of Texas at Brownsville,Brownsville, astronomy through the detection of many events per year.To Texas 78520.USA. test some of Advanced LIGO's new technologies and to in- DPresent address:LIGO Laboratory,Califoria Institute of Technology. Pasadena,California 91125,USA. crease the chances of detection through a more sensitive data g)Present address:NASA Langley Research Center,Hampton,Virginia taking run,an incremental upgrade to the detectors was car- 23666.USA. ried out after S5.5 This project,Enhanced LIGO,culminated 0034-6748/2012/83(3)/033109/12/S30.00 83,033109-1 2012 American Institute of Physics Reuse of AlP Publishing content is subject to the terms at:https://publishing.aip.org/authors/nghts-and-permi D0wmlo8 d to IP:183.195251.60Fi.22Apr2016 00:54:10REVIEW OF SCIENTIFIC INSTRUMENTS 83, 033109 (2012) Thermal effects in the Input Optics of the Enhanced Laser Interferometer Gravitational-Wave Observatory interferometers Katherine L. Dooley,1,a) Muzammil A. Arain,1,b) David Feldbaum,1 Valery V. Frolov,2 Matthew Heintze,1 Daniel Hoak,2,c) Efim A. Khazanov,3 Antonio Lucianetti,1,d) Rodica M. Martin,1 Guido Mueller,1 Oleg Palashov,3 Volker Quetschke,1,e) David H. Reitze,1,f) R. L. Savage,4 D. B. Tanner,1 Luke F. Williams,1 and Wan Wu1,g) 1University of Florida, Gainesville, Florida 32611, USA 2LIGO, Livingston Observatory, Livingston, Louisiana 70754, USA 3Institute of Applied Physics, Nizhny Novgorod 603950, Russia 4LIGO, Hanford Observatory, Richland, Washington 99352, USA (Received 9 December 2011; accepted 23 January 2012; published online 23 March 2012) We present the design and performance of the LIGO Input Optics subsystem as implemented for the sixth science run of the LIGO interferometers. The Initial LIGO Input Optics experienced thermal side effects when operating with 7 W input power. We designed, built, and implemented improved versions of the Input Optics for Enhanced LIGO, an incremental upgrade to the Initial LIGO inter￾ferometers, designed to run with 30 W input power. At four times the power of Initial LIGO, the Enhanced LIGO Input Optics demonstrated improved performance including better optical isolation, less thermal drift, minimal thermal lensing, and higher optical efficiency. The success of the Input Optics design fosters confidence for its ability to perform well in Advanced LIGO. © 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3695405] I. INTRODUCTION The field of ground-based gravitational-wave (GW) physics is rapidly approaching a state with a high likelihood of detecting GWs for the first time in the latter half of this decade. Such a detection will not only validate part of Ein￾stein’s general theory of relativity, but also initiate an era of astrophysical observation of the universe through GWs. Gravitational waves are dynamical strains in space-time, h = L/L, that travel at the speed of light and are gener￾ated by non-axisymmetric acceleration of mass. A first de￾tection is expected to witness an event such as a binary black hole/neutron star merger.1 The typical detector configuration used by current gen￾eration gravitational-wave observatories is a power-recycled Fabry-Perot Michelson laser interferometer featuring sus￾pended test masses in vacuum as depicted in Figure 1. A diode-pumped, power amplified, and intensity and frequency stabilized Nd:YAG laser emits light at λ = 1064 nm. The laser is directed to a Michelson interferometer whose two arm lengths are set to maintain destructive interference of the re￾combined light at the anti-symmetric (AS) port. An appropri￾ately polarized gravitational wave will differentially change a)Author to whom correspondence should be addressed. Electronic mail: kate.dooley@aei.mpg.de. Present address: Albert-Einstein-Institut, Max￾Planck-Institut für Gravitationsphysik, D-30167 Hannover, Germany. b)Present address: KLA-Tencor, Milpitas, California 95035, USA. c)Present address: University of Massachusetts–Amherst, Amherst, Massachusetts 01003, USA. d)Present address: École Polytechnique, 91128 Palaiseau Cedex, France. e)Present address: The University of Texas at Brownsville, Brownsville, Texas 78520, USA. f)Present address: LIGO Laboratory, California Institute of Technology, Pasadena, California 91125, USA. g)Present address: NASA Langley Research Center, Hampton, Virginia 23666, USA. the arm lengths, producing signal at the AS port proportional to the GW strain and the input power. The Fabry-Perot cavi￾ties in the Michelson arms and a power recycling mirror (RM) at the symmetric port are two modifications to the Michelson interferometer that increase the laser power in the arms and therefore improve the detector’s sensitivity to GWs. A network of first generation kilometer scale laser in￾terferometer gravitational-wave detectors completed an in￾tegrated 2-year data collection run in 2007, called Science Run 5 (S5). The instruments were: the American Laser Inter￾ferometer Gravitational-Wave Observatory (LIGO),2 one in Livingston, LA with 4 km long arms and two in Hanford, WA with 4 km and 2 km long arms; the 3 km French-Italian detector VIRGO (Ref. 3) in Cascina, Italy; and the 600 m German-British detector GEO (Ref. 4) located near Hannover, Germany. Multiple separated detectors increase detection confidence through signal coincidence and improve source lo￾calization via waveform reconstruction. The first generation of LIGO, now known as Initial LIGO, achieved its design goal of sensitivity to GWs in the 40–7000 Hz band, including a record strain sensitivity of 2 × 10−23/ √Hz at 155 Hz. However, only nearby sources produce enough GW strain to appear above the noise level of Initial LIGO and no gravitational wave has yet been found in the S5 data. A second generation of LIGO detectors, Ad￾vanced LIGO, has been designed to be at least an order of magnitude more sensitive at several hundred Hz and above and to give an impressive increase in bandwidth down to 10 Hz. Advanced LIGO is expected to open the field of GW astronomy through the detection of many events per year.1 To test some of Advanced LIGO’s new technologies and to in￾crease the chances of detection through a more sensitive data taking run, an incremental upgrade to the detectors was car￾ried out after S5 .5 This project, Enhanced LIGO, culminated 0034-6748/2012/83(3)/033109/12/$30.00 © 2012 American Institute of Physics 83, 033109-1 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 00:54:10