Download Laser Safety for LIGO Peter King 8 Annual DOE Laser Safety Officer Workshop

Laser Safety for LIGO
Peter King
8th Annual DOE Laser Safety Officer Workshop
September 12th, 2012
LIGO‐G1200825‐v1
An Overview of LIGO
 LIGO is the Laser Interferometer Gravitational Wave Observatory
 A large scale, dual recycled Michelson interferometer with 4 km long arms
 World’s largest UHV system with a volume of 343400 cubic feet at ~10‐9 torr
 Beam tubes are straight to within 5 mm over 4 km
 200 W single mode, single frequency Nd:YAG laser
 12 m long modecleaner
 0.5 m long output modecleaner
 Test masses are 40 kg, 340 mm diameter by 200 mm thick
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LIGO Observatories
 Currently two observatories, one pending
 Hanford, WA
 Livingston, LA
 Somewhere in India – site selection currently underway
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The Mission of LIGO
 Gravitational waves were predicted by Einstein’s General Theory of Relativity
 Sources of gravitational waves include
 Coalescing binary systems such as a black hole – black hole, or a
black hole – neutron star, neutron star – neutron star
 Supernovae
 The existence of gravitational waves has been inferred by orbital decay of pulsars
 Hulse – Taylor binary pulsar (PSR 1913+16, discovered in 1974)
 LIGO aims to directly measure gravitational waves
 Forces are incredibly small
 LIGO displacement sensitivity is 10‐19 meters, about 1/10000th the diameter of a nucleus
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Safety at LIGO
 Laser safety is just one aspect of the safety umbrella which also includes
 Chemical safety
 Electrical safety
 CPR and First Aid
 Hazards analysis
 Workers should be familiar with, and have taken part in the writing of the hazards analysis
 Failure modes and effects analysis (FMEA)
 Work permit meeting (at the observatories)
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Laser Safety
 Basic laser safety training
 Presentation and quiz
 Commercial training videos
 On‐the‐job training (OJT)
 No explicit alignment training
 Assigned mentor
 Relies on the experience of the mentor
 Mentor largely decides when candidate is qualified
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Workers
 LIGO not only encompasses two campuses and observatories but is part of the LIGO Virgo Collaboration (LVC)
 Each site has an LSO
 1448 participants at last count, ~180 directly work in or around lasers
 Workers consist of graduate students, postdocs, technical staff, contract labour, engineering and scientific staff
 Wide range of experience
 From none at all to plenty
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Work Environment
 Lasers and optics are typically enclosed in a cleanroom environment or enclosure
 Interferometer sensors are either in vacuum or in an acoustic enclosure
 Access control
 Areas are accessed via access cards
 Zone access levels with tiers
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Multiple Wavelengths
 We have a number of wavelengths and output powers present at LIGO ranging from the visible to the far infrared
 532 nm – ALS, arm length stabilisation
 635 nm – OptLev, optical levers
 808 nm – pump diodes
 900 nm – Hartman sensor
 950 nm – Hartman sensor
 1047 nm – Pcal, photon calibrator
 1064 nm – PSL, pre‐stabilised laser
 10.6 m – TCS, thermal compensation system
 Decided to tackle the laser safety eyewear issue by having one type to suit all
 Reduces the risk of cross contamination
 Makes a choice of laser safety eyewear difficult
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Skin Protection
 Tried to find suitable gloves to provide skin protection when manipulating beams.
 Flame resistant
 Flexible enough to allow dexterity to manipulate mirror mount adjusters
 Comfortable
 Hard to find
 Tried Nomex” and CarbonX” gloves
 We did not find any suitable pairs.
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Special Considerations
 Use of super polished optics to minimise scattered light
 Surface roughness § 1 Å, flatness /10 and scratch‐dig § 10‐5
 Many laser safety tools are a noise source for the interferometer through
 Acoustic coupling
 Movement of protective screens due to air currents
 Scattered light
 Reflections off the inside of beam tubes
 Power meters and photodiodes
 Dirty optics
 Parasitic reflections off super‐polished optics and vacuum viewports
 Cleanroom clothes
 Increased fogging of laser safety eyewear
 Static electricity discharge
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Equipment Considerations
 Contamination of optical surfaces
 Do not use commercial razor blade style beam blocks
 Oil vapours from warm beam blocks
 Laser generated airborne contaminants
 Carbon fibre‐based materials, for example Vel‐Black”
 Caution when using ceramic or phosphor IR viewing cards
 Caution when using power meters
 Brewster angle beam blocks to minimize back reflections
 Black glass for low power applications
 Silicon carbide for high power applications
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Incident Threshold
 With increased laser power, we need to consider scattered light
 2 mW, over a 7 mm diameter aperture, threshold limit 12
Incident Reporting
 Following discovery of a stray beam
 If under the threshold
 Fix situation, LSO deals with matter
 If above the threshold
 Laser is shutdown
 Investigation by LSO
 Approval by Directorate required prior to turning the laser back on
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Other Hazards
 One needs to be aware of other hazards present …
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