Laser Safety for LIGO

Transcription

1 Laser Safety for LIGO Peter King 8 th Annual DOE Laser Safety Officer Workshop September 12 th, 2012 LIGO G v1

2 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 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 1

3 LIGO Observatories Currently two observatories, one pending Hanford, WA Livingston, LA Somewhere in India site selection currently underway 2

4 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 , discovered in 1974) LIGO aims to directly measure gravitational waves Forces are incredibly small LIGO displacement sensitivity is meters, about 1/10000 th the diameter of a nucleus 3

5 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) 4

6 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 5

7 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 6

8 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 7

9 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 8

10 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. 9

11 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 10

12 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 11

13 Incident Threshold With increased laser power, we need to consider scattered light 2 mw, over a 7 mm diameter aperture, threshold limit 12

14 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 13

15 Other Hazards One needs to be aware of other hazards present 14