LIGO-G000298-00-W

Performance of the LIGO I PSLat the

LIGO Hanford Observatory

Rick SavageLIGO Hanford Observatory

Laser Zentrum HannoverNovember 15,2000

High-power Laser Development Meeting

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Chronology

2-km Interferometer PSL» Begin installation – Fall 1998

» Begin operation – December 1998– Frequency servo (FSS)operational– PMC servo operational– Power stabilization servo (ISS) operational

» 15-m modecleaner on-line

4-km Interferometer PSL» Begin installation – 10/00

– Power up laser – 10/00

» Simplified optical layout

High-power Laser Development Meeting

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Topics …

LIGO 10-W laser » Reliability

– Head– Power supply

» Output power stability

» Beam quality

» Frequency stabilization– Present noise level– Noise sources

Mount resonances Acoustic coupling Table leg resonances Doppler shifts from bulk motion Simplified optical layout

High-power Laser Development Meeting

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… Topics

Pre-modecleaner» Atmospheric pressure sensitivity

» Finesse too low

» Cavity losses

High-power Laser Development Meeting

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10-W Laser Reliability …

Head –» >16,000 hours continuous operation without adjustment

» Output power 8 watts– Power decreases when either MO or PA current increased

Re-alignment not attempted – complicated by EOM between MO and PA

» Beam quality - PMC visibility >93%

High-power Laser Development Meeting

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… 10-W Laser Reliability

Power supply - » Rotary encoder failures ~ 3 times

– Unable to reduce PA diode current– <one hour to replace in field

» PS fault failures ~ 20 times– Suspect over-voltage protection circuitry– Defeating circuitry may have helped on some supplies

High-power Laser Development Meeting

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Frequency Stabilization

High-power Laser Development Meeting

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Frequency noise – mount resonances

- All New Focus mounts replaced with Newport U100A mounts-Lab measurements indicate New Focus clamping forks undesirable

U100 A mounts preferred, Klinger mounts slightly worse

High-power Laser Development Meeting

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Frequency noise - enclosure acoustics

- Reverberation time of enclosure reduced.- Little affect on the mount resonances.

High-power Laser Development Meeting

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Frequency noise – table acoustics

- Acoustics driving bottom of optical table- Acoustic skirt for table being designed.

High-power Laser Development Meeting

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Freq. noise – Table motion Doppler shifts

Table and reference cavity acceleration

Table

Ref. Cav.

Freq. noise from Doppler shift

Doppler shift ~ fo(v/c) = v/ = a/(2f-Longitudinal table motion not the cause of noise-Vertical motion suspect – rotating periscope??

High-power Laser Development Meeting

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Frequency noise – table leg resonances

Bolts tightBolts loose

Six adjustable legsBeing replaced withthree fixed legs

High-power Laser Development Meeting

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Revised Optical Layout

High-power Laser Development Meeting

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Frequency glitches

FSS Fast

PMC Error

PMC Error

Ref. Cav.RFPD DC

-Observed at rate of 10’s per second- Eliminated by adjusting NPRO pump diode currentby 0.02 amps

High-power Laser Development Meeting

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Pre-modecleaner - performance

Noise PSD ratio of ~ 5 >> fc ~ 0.8 MHz

fc for present PMC ~ 1.7 MHz >> ASD ~ 2 x req.

High-power Laser Development Meeting

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Pre-modecleaner – atmospheric pressure

strain ~ 2.7 x 10-9 per Pascal

Sensitivity to atmosphericpressure changes

High-power Laser Development Meeting

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Pre-modecleaner - losses

Pin = 7.84 W

Pout = 6.8 W

T = Pout/ Pin = T2 / (L+T)2

T= 1.45% Measure: T = Pout / (Pin x visibility) = 0.93 >> L = 515 ppm per mirror

High-power Laser Development Meeting

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Relative power fluctuations

9/11/00 11/07/00

Atmosphericpressure in LVEA

10-W laseroutput powermonitor insidehead

7.7 W

8.1 W

60 days