LIGO-G050478-00-W Commissioning and Performance of the LIGO Interferometers Reported on behalf of...

LIGO-G050478-00-W

Commissioning and Performance of the LIGO Interferometers

Reported on behalf of LIGO colleagues by

Fred Raab, LIGO Hanford Observatory

(Substituting for Brian O’Reilly, LIGO Livingston Observatory, whose trip was cancelled by Hurricane

Katrina)

LIGO Detector Commissioning 2LIGO-G050478-00-W

Time Line

NowInauguration

1999 2000 2001 2002 20033 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

E2Engineering

E3 E5 E9 E10E7 E8 E11

First Lock Full Lock all IFO

10-17 10-18 10-20 10-21

2004 20051 2 3 4 1 2 3 4 1 2 3 4

2006

Runs

First Science Data

S1 S4Science

S2 S3 S5

10-224K strain noise at 150 Hz [Hz-1/2]


Schematic of Initial LIGO Detector (LIGO-1)

suspended mirrors markinertial frames

antisymmetric portcarries GW signal

Symmetric port carriescommon-mode info


What Limits Sensitivityof Interferometers?

• Seismic noise & vibration limit at low frequencies

• Atomic vibrations (Thermal Noise) inside components limit at mid frequencies

• Quantum nature of light (Shot Noise) limits at high frequencies

• Myriad details of the lasers, electronics, etc., can make problems above these levels


Vibration Isolation Systems

» Reduce in-band seismic motion by 4 - 6 orders of magnitude» Little or no attenuation below 10Hz» Large range actuation for initial alignment and drift compensation» Quiet actuation to correct for Earth tides and microseism at 0.15 Hz during

observation

HAM Chamber BSC Chamber


Core Optics

Substrates: SiO2

» 25 cm Diameter, 10 cm thick

» Homogeneity < 5 x 10-7

» Internal mode Q’s > 2 x 106

Polishing» Surface uniformity < 1 nm rms

» Radii of curvature matched < 3%

Coating» Scatter < 50 ppm

» Absorption < 2 ppm

» Uniformity <10-3

Production involved 6 companies, NIST, and LIGO


Core Optics Suspension and Control

Shadow sensors & voice-coil actuators provide

damping and control forces

Mirror is balanced on 30 microndiameter wire to 1/100th degree of arc

Optics suspended as simple pendulums


Pre-stabilized Laser (PSL)

Custom-built10 W Nd:YAG Laser,

joint development with Lightwave Electronics

(now commercial product)

Frequency reference cavity (inside oven)

Cavity for defining beam geometry,

joint development withStanford


IO

Frequency Stabilization of the Light Employs Three Stages

Pre-stabilized laser delivers light to the long mode cleaner

• Start with high-quality, custom-built Nd:YAG laser

• Improve frequency, amplitude and spatial purity of beam

Actuator inputs provide for further laser stabilization

• Wideband• Tidal

10-WattLaser

PSL Interferometer

15m4 km


Feedback & Control for Mirrors and Light

Damp suspended mirrors to vibration-isolated tables» 14 mirrors (pos, pit, yaw, side) = 56 loops

Damp mirror angles to lab floor using optical levers» 7 mirrors (pit, yaw) = 14 loops

Pre-stabilized laser» (frequency, intensity, pre-mode-cleaner) = 3 loops

Cavity length control» (mode-cleaner, common-mode frequency, common-arm, differential

arm, michelson, power-recycling) = 6 loops

Wave-front sensing/control» 7 mirrors (pit, yaw) = 14 loops

Beam-centering control» 2 arms (pit, yaw) = 4 loops


Digital Interferometer Sensing & Control System


LIGO-1 Signal Recovery Configuration

ASREFL

POB


Now Look at LSC Screen


AS, PO, REFL Inputs


Input Matrix Decodes Input into DARM, CARM, MICH, PRC


Separate Filtering and Gain Sections for Each Loop


Output Matrix Translates Loop Feedback into Actuator Signals


Digital Controls screen example A

nal

og

In

An

alo

g O

ut

Digital calibration input


LIGO Sensitivity Over TimeLivingston 4km Interferometer

May 01

Jan 03


Interferometer Strain Sensitivity


It works! Long-term search begins Nov05


Why is Locking Difficult?

One meter

Human hair, about 100 microns000,10

Wavelength of light, about 1 micron100

LIGO sensitivity, 10-18 meter000,1

Nuclear diameter, 10-15 meter000,100

Atomic diameter, 10-10 meter000,10

Earthtides, about 100 microns

Microseismic motion, about 1 micron

Precision required to lock, about 10-10 meter


Run S3 S4

L1 21.8% 74.5%

H1 69.3% 80.5%

H2 63.4% 81.4%

Triple 15.8% 56.9%

Progress: Duty Cycle


Why Had Duty Cycle Been Lower in Livingston


Improved Isolation with the Hydraulic External Pre-Isolator (HEPI)

Adv. LIGO approach, accelerated & adapted for use in initial LIGO


HEPI


HAM

BSC

Active External Pre-Isolators

Seismic Retrofit at Livingston


One-Arm Test of External Pre-Isolation Confirms Performance


Thermal Compensation

Over-heat Correction

Inhomogeneous Correction

Under-heat Correction

CO2

Laser

?

ZnSe Viewport Over-heat pattern

Inner radius = 4cm Outer radius =11cm

Cold power recycling cavity is unstable: poor buildup and mode shape for the RF sidebands

ITM thermal lens power of ~0.00003 diopters needed to achieve a stable, mode-matched cavity

intended to be produced by ~25 mW absorbed from 1μm beam

ITM


Sideband Images as Function of Thermal Heating

No Heating 30 mW 60 mW 90 mW

120 mW 150 mW 180 mW Input beam

Best match


101

102

10-19

10-18

10-17

10-16

10-15

10-14

Frequency [Hz]

Dis

pla

ce

me

nt

[m/

Hz]

L1: 8.9 Mpc, Aug 12 2005 05:48:43 UTC

L-Mirror ThermalWire ThermalDark NoiseIntensity NoiseFrequency NoiseShot NoiseLocal DampingSeismicPRC -> DARMMICH -> DARMOscillator PhaseOptical LeversWFSETM electronicsITM electronicsTotalRequirement

Close-up of estimated noise sources for L1


Ongoing story of photodiode damage

Loss-of-lock: full beamsplitter power can be dumped out the AS port, in a ~10 msec width pulse

» Mechanical shutter cuts off the beam, with a trigger delay of about 6 msec

PD damage due to» Too high trigger level» Shutter too slow (wrong type)

Damaged PDs can be noisy Solution (in progress):

» All shutters of proper type» Carefully set trigger level» Looking at cutting off PD bias

voltage on lock-loss

~100 W

5 msec

Red: replaced damaged PDs


Upconversion from stack motion

Using HEPI, increase the suspension point motion at 1.5 Hz by a factor of 5

DARM noise increases by a factor of ~5 over a wide band

Effect first seen at LHO, & measured recently at LLO:


Scattered light fringe wrappingB

RT

ITMETM

Esc~10 -10 E0

)sin( sct

Data looks a lot like what you’d expect from scattered light Don’t know where light is scattering off Beam tube baffles were made to cut stray rays: 270 mm

aperture May be possible to use feedback to reduce optical table motion


Closing remarks…

Progressive sensitivity improvements have achieved design goals

Early implementation of Advance LIGO techniques helped achieve goals» HEPI for duty-cycle boost

» Thermal compensation of mirrors for high-power operation

Some technical issues being worked to improve long-term robustness and reliability» Loss-of-lock protection for photodiodes

» Upconversion mitigation

Believe still room for post-S5 improvements

LIGO-G050478-00-W Commissioning and Performance of the LIGO Interferometers Reported on behalf of...

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