Researchers have developed and tested a new locking method for gravitational wave detectors that will advance the discovery of distant black holes and neutron stars colliding.
Researchers from ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) nodes at The University of Western Australia, the Australian National University and the University of Adelaide co-authored the study published in Physical Review D.
Lead author Dr Jian Liu, from UWA's School of Physics, Mathematics and Computing, said gravitational wave detectors, such as LIGO, detected ripples in space-time created by colliding black holes by measuring changes in distance one thousand times smaller than the width of a proton.
"To do this, the detector's 40-kilogram mirrors, which sit four kilometres apart, must be locked in exactly the right positions using laser light," Dr Liu said.
"Before the detector can start listening to the universe, the mirrors must be gently brought to rest and locked in place by a system called arm-length stabilisation or the locking system.
"The next upgrade of LIGO will use new crystalline mirror coating technology to improve sensitivity, but the coating absorbs the green laser light the current locking system relies on."
Researchers developed and tested a new locking scheme using infrared light (1596 nanometres), a colour the new coatings do not absorb.
Special crystals were used to convert the frequency of the light, changing the locking infrared light (1596 nm) and the detector's main (1064nm) laser light into green light, which allowed control to be handed over smoothly from the locking laser to the main laser.
"We demonstrated a stable hand-over from the locking laser to the main laser that took about 60 seconds, which is much faster than the current system, and repeated it successfully over several days," Dr Liu said.
"Based on these results, we estimate the measurement error between the lasers to be incredibly small – about one-tenth the width of an atom even when measuring along a four-kilometre LIGO laser arm."
The findings show a practical locking method exists for gravitational wave detectors that use the new low-noise crystalline mirror coatings.
UWA co-author Dr Carl Blair, who regularly works at detectors in the US and Japan, said it was amazing to see this new technology working and it would allow humans to listen to the edge of the universe.
