The LIGO Instruments Stan Whitcomb NSB Meeting LIGO

The LIGO Instruments Stan Whitcomb NSB Meeting LIGO Livingston Observatory 4 February 2004 LIGO- G 040011 -02 -D NSB Meeting

The Detection Challenge Seismic motion-ground motion due to natural and anthropogenic sources L ~ 4 km For h ~ 10– 21 DL ~ 10 -18 m Thermal noise-vibrations due to finite temperature- LIGO- G 040011 -02 -D Shot noise-quantum fluctuations in the number of photons detected NSB Meeting 2

Initial Interferometer Design Noise Budget • Understanding of noise sources developed with 40 m prototype • Limiting noise (with available technology) detectable signal zone » Seismic at low frequencies » Thermal at mid frequencies » Shot noise at high frequencies • Facility limits much lower to allow improved detectors as technology matures LIGO- G 040011 -02 -D NSB Meeting 3

Optical Configuration Power Recycled Michelson Interferometer with Fabry-Perot Arm Cavities end test mass 4 km Fabry-Perot arm cavity “typical” photon makes 200 x 50 bounces—requires reflectivity 99. 99% recycling mirror input test mass Laser signal LIGO- G 040011 -02 -D beam splitter NSB Meeting 4

Stabilized Laser Custom-built 10 W Nd: YAG laser— Now a commercial product LIGO- G 040011 -02 -D Stabilization cavities for laser beam— Widely used for precision optical applications NSB Meeting 5

LIGO Optics Substrates: Si. O 2 High purity, low absorption Polishing Accuracy < 1 nm (~10 atomic diameters) Micro-roughness < 0. 1 nm (1 atom) Coating Scatter < 50 ppm Absorption < 0. 5 ppm Uniformity <10 -3 (~1 atom/layer) Worked with industry to develop required technologies 2 manufacturers of fused silica 4 polishers 5 metrology companies/labs 1 optical coating company LIGO- G 040011 -02 -D NSB Meeting 6

Optics Suspension and Control LIGO- G 040011 -02 -D • Suspension is the key to controlling thermal noise • Magnets and coils to control position and angle of mirrors NSB Meeting 7

Core Optics Installation and Alignment • LIGO- G 040011 -02 -D Cleanliness of paramount importance NSB Meeting 8

Seismic Isolation • Cascaded stages of masses on springs (same principle as car suspension) damped spring cross section LIGO- G 040011 -02 -D NSB Meeting 9

Seismic Isolation In air 102 100 10 -2 10 -4 10 -6 Horizontal 10 -6 In vacuum 10 -8 Vertical 10 -10 LIGO- G 040011 -02 -D NSB Meeting 10

Commissioning Progress LIGO- G 040011 -02 -D NSB Meeting 11

Science Runs as Sensitivity Improves S 3 Duty Cycle Hanford 4 km 69% Hanford 2 km 63% Livingston 4 km 22%* S 1 st 1 Science Run Sept 02 (17 days) S 2 Science Run Feb - Apr 03 (59 days) 2 nd LIGO Target Sensitivity * Limited by high ground noise S 3 Science Run Nov 03 – Jan 04 (70 days) 3 rd LIGO- G 040011 -02 -D NSB Meeting 12

Seismic Environment at LLO Test at MIT • Anthropogenic ground vibrations » Related to human activity – mostly logging CROSSBEAM OFFLOAD SPRINGS • • HYDRAULIC ACTUATOR (HORIZONTAL) HYDRAULIC LINES & VALVES Microseism due to ocean waves Strategy for recovering full-time duty at LLO » Use Hydraulic External Pre-Isolator (HEPI) system developed for Adv. LIGO » Prototype tested at Stanford and MIT » Fabrication nearly complete, installation just beginning PIER LIGO- G 040011 -02 -D NSB Meeting 13

Summary • • Jump from laboratory-scale to kilometer-scale interferometers has been successful Commissioning on track » Sensitivity nearing design level » Reliability and duty cycle as expected for this stage » Active seismic isolation development addresses excess seismic noise at LLO, as well as Advanced LIGO requirements • Interleaving of Science Runs with commissioning » Science begins » Analysis community prepares for full operation – Development of analysis algorithms, grid computing, … LIGO- G 040011 -02 -D NSB Meeting 14